This is a simple guide to making your own boat, with some of the options available today.
As prices go through the roof, and build quality and design falls before the desire for greater profits, many people are building their own boats. Many are making superior boats at far less cost than the commercial designs. If interested, try this now before your Labour MP and their fiends decide that this too, is another way to make more stealth taxes to fleece the ordinary and honest Brit.

Due to a torrent of Blair's stupid laws ruining modern Britain, and a plague of parasitic lawyers, no-one may read nor act upon any information they may read here. Stop reading now.

Introduction.
This monograph is a rough guide to how you may wish to approach the building of your own boat. You will need to delve deeper into the subtleties and refinements, but this monograph may give an overview of the options available today.

The main engineering skills option I'd like to stress is that you don't have to pay through the nose for a boat. The only real cost is the cost of mooring, but if you can transport your craft to the slipway, then there should be no cost. Because many boats are too large to transport, then always make sure you can get a mooring first. In many cases, putting your name down for a mooring can be done at the same time as you start your build in the back garden, so that in the next couple of years, a mooring will become available. Check the mooring size limit and crane sizes.

As the rich get richer and the poor get poorer, many locals are being displaced from local moorings by rich outsiders. So always do what you can to discourage all parasitic outsiders. Some folk no longer help those who obviously live elsewhere or are just 'boatie' prats, or heavily overcharge them.
(In modern Britain, many outsiders have no intention to pay for the work done, so always get money up front and fit core booby traps and enhanced corrosion into your work, should they fail to pay up. I have been phoned from Spain by those whose wiring I have done, but failed to pay me for my work. Their electrics strangely failed. They were towed home, which cost a lot more than paying the workman who would have 'fully checked' the final system for total reliability.)

A classic picture to show that even the massive ferry makes less wash than the 'boatie' prat in the foreground. The little boat behind can happily manage the ferry wash, but the foreground 'prat wash' is just plain stupid and pisses everyone off.
It is particularly annoying when you are in a small racing yacht and getting up to a fine top speed, only to have yet another a boatie prat spoil otherwise beautiful and perfect sailing conditions for everyone else. It is no wonder that so many Plymothians dislike the certain 'big white boat' factory in this otherwise fine marine city.
You may also wish to note the ballasting and pitch angle of the hull and consider if this is an efficient or safe boat. I know of many who can make much better boats at home in their gardens.

Watch Your Wake! You can be responsible for any damage or injury caused by it.

The main social skill I'd like to stress is that you don't have to be a prat on a big poncy white power boat, pissing off all other boat owners around our coasts with your wash.
Like 4x4's in Chelsea and Manhattan, power boats and ginpalaces are never welcome by sensible people in a sensible world. No one is impressed apart from bimbos and bimboys. - So if you are such a prat, please sod off to prat land, along with the likes of those who many of us dislike, such as terrorists, politicians, lawyers and freemasons.

For the rest of us with some imagination and decent social skills, there are many types of boats and ways to enjoy our fine planet.

From canal barges to high speed yachts. Hydrofoils, hovercraft and ekranoplans, both personal and massive. (Yes, personal hydrofoils using leg power, see piccie) and the Moth class small yachts with hydrofoils. At the same end of the scale, there are fast water canoes and surfboards, to ocean kayaks and all forms of rafts.
This monograph mainly concerns small day boats and yachts, about the one to four crew range.

The materials used for these boats are fantastic in uses and methods.
From injection moulded plastic canoes to concrete yachts. From prefabricated steel hull flat packs of racing yacht hulls to the superb craftsmanship of a polished wooden lakeside steamer. (Polished in both finish and style.) From the rubberised cloth of a liferaft to the tin drums lashed together of a village raft race. From the plastic bag of clothes of someone surviving in the sea, to the carbon fibre hull of a racing catamaran.
From the incredible manual dexterity and subtle skills of a beech bark canoe to the utter gross and ecologically appalling, fuel-wasting glass fibre and obscene powerboats and gin palaces of the ultimate 'sea prats'.

The art of boat building is phenomenal, from oppressively ecological, through very sensible, to totally stupid, and that's putting it mildly.

With all these options, there is yet another level of options and that's in hull design: Of the shape and form of the water interface. From stable barge, through the bobbing liferaft, to the unstable surfboard. From the self stabilising aircraft carrier to the little boat with outboard motor trying to remain upright while bobbing across someone else's wake.

The power sources for boats are also wide and often unreliable.
The sail has many forms, from traditional square rig of tea clippers and Chinese Junks, through traditional Gaff rigs, the modern triangular sails to the future vertical aerofoil.
Hand power ranges from a single sculling paddle, to rowing across the Pacific. Legs are always a powerful component in oar racing. Leg power is becoming more applicable, even for hydrofoils.

Engine power is the ubiquitous diesel and common for most sensible boats, to the rise of the horrible, large Italian V12, totally ecologically unfriendly racing engines, to the steady four storey monster 'cathedral engines' on ocean liners and tankers. From the nuclear power of the SS Savannah, to the simple paddle. From the jet engines of ferries and frigates, to the humble Japanese mini outboard, and small electric motors for pond and lake fishing.
The teensy Yanmar two cylinder diesel opposite may look humble, but they are the worlds largest marine diesel manufacturer. A lovely little piece of marine engineering - totally reliable !

Using the power is also a wide arena of choices. The innovative screw drive propeller used on Brunels SS Gt. Britain, (Bristol) is now a wide ranging device, from the common petal propeller through the ducted impeller drive of wet bikes and the hydro pump. From the ancient paddle wheel, to the vertical blades of a Voith Schnieder tug drive to the futuristic electro static drive using magnetism and electricity to force sea water through a pipe.

Therefore, choosing and building a boat is not quite such a simple task. But great fun.

The first task is to decide what you want it for.
Many want a fast, big powerboat which 'looks good', simply because they have little imagination. They often buy such horrors, only to find that the running costs are even uglier. Some pretentious plonkers I know can only afford to take to sea once a month. If we all acted like these prats the seas would be a mess - I still get eye, ear and throat infections every time I swim in Plymouth waters as these prats throw their junk overboard including condoms and sanitary towels. These prats also buy the large, blocks of 'ghost flats' which despoil our once historical Barbican area, and the increasingly uglier coastline. Until these prats disappear or are encouraged to bugger off, there may be little hope for sensible folk to enjoy our superb coasts.
Try to look after your city and never support, nor turn a blind eye to Council corruption, who may sell your heritage cheap to thier developer friends.
I dislike Freemasonry.
(Plymouth barbican before developers. From my Guide to Dartmoor.)

In a nicer world, at the sensible end of the scale is a home made yacht which is easily taken to the slipway and sailed all day for zero cost. Even motor boats with a sensible diesel can pootle around the coast all day for a few pound coins, and usually catch enough fish for many a healthy family meal.

There are many ordinary Brits who enjoy boating and sailing on a regular basis and like most of us, are environmentally aware and socially responsible. This way we can remain a seafaring nation to be proud of.
So always try your hand at sailing or boating, but do it sensibly and not with a stupid power boat. In the same manner that hooligans in fast cars are unwanted on roads, causing untold harm and consternation, so too are such prats unwanted at sea.
If you treat the sea with respect, you are less likely to come to harm and far more likely to enjoy the pleasures of our wonderful coastlines and oceans.

( One of my friends has moorings and running costs which came to less than a thousand pounds in the first year and that includes the cost of a 24 foot motor boat ! This includes two trips a week, and admittedly we had to rewire it and fix the sea cooling pump, but that cost nothing and took almost no time at all. Runs for about a quid an hour in fuel. A very sensible and eminently happy boat. Others have small home-made racing dinghies which are thoroughly enjoyed at weekends and many evenings, with zero running costs.)

After choosing your budget and a sensible range of potential vessels:
The next is how to power it.
Then to choose the best hull for the job.
Then to decide the best materials and method of construction.
Then a maintenance routine to keep it safe and reliable.

During all this time you will be reading up on navigation and marine law, 'ship to shore radio' procedures and how to listen, your duties and responsibilities, the civilities and politeness. Also learn how to swim to stay alive and understand and practice first aid, command and survival for yourself and anyone in your boat for whom you automatically become responsible.

Choosing a boat and general hull design.

Hull design is an ancient art, and yet incredibly modern too.
It is vitally important to understand that there is already the perfect hull for you out there somewhere, and in use by someone.
Therefore make all possible attempts to refine your search to a handful of the best possibilities, then talk to the owners and watch the boats in various waters. You are NOT looking at the superstructure, but hull design and how the hull sits in the water for your desired options. There are many similar hulls, all with differing superstructures.
Just sitting on a high shoreline with binoculars on a sunny day with a fine wind, to check the handling of various yachts is highly recommended. This may well be done many times throughout the season or whole year, depending upon use. The same applies to powerboats, canoes, canal barges and all other forms of boating. Not all sailors are very good and their craft.

(Only idiots go to a boat show, like the look of a boat and pay through the nose for it, then take to sea without any idea what they are doing. There are many 'prat boats' tied up in Plymouth and around the coasts of Britain and much of the world too. The owners are commonly referred to by the derogatory term 'boaties'. )

After an initial list of desired uses and suitable hulls, then you must try to get a day out on a similar boat. In modern Britain, this is increasingly difficult due to parasitic lawyers, as many boat owners no longer take strangers out for the day. My friends have such boats but no longer take strangers out for a days fishing even in if they pay well and supply excellent food and drink. Taking a bottle of nice wine and minimalist cooking gear - to go fishing for a nice cod to go with the wine, is real fishing.
Today, be it fishing, cruising or pleasure trips, you may have to hire a boat or become friendly with decent boat owners to get first hand assessment of your final choices. Good luck, but at least by choosing a sensible boat, you will be more likely to meet some sensible people.

A day out will allow you to assess the craft in all sorts of waters, - close navigation on leaving harbour and navigation channels, then looking for the bow waves of tankers or a local massive car ferry to see how she behaves beam on, head on and stern up on a following wave. After this, you must assess the boat and owner carefully before taking to the high seas. (Preferably do a quick apprenticeship as crew on an inshore trawler for a few days if you can't get any other option 'to know the ropes'.)

What you are looking for is the stability and efficiency of the hull, how it behaves in all conditions and whether it can be improved. All boats roll and it is how they behave compared to others that counts. Just because a boat rocks more than another does not mean it's less stable as it may well take heavy seas far better. Understanding stability graphs is useful, see later.
You will need to go out in all safely acceptable weathers to get the best knowledge.
Tell the owner of the hire day boat that you wish to asses the hull in inclement weather or out of season and he or she may well put to sea for you for a few hours, as most other (better) days are usually pleasure trips needed for regular income.
When pottering around the harbour and meeting the owners or crew, ask what is the cruising speed, and fuel consumption and if it handles well in a heavy sea, or does it slap up and down badly on the waves or does it run with the waves reasonably well.

A home made boat with a superb hull, but a daftly designed or ballasted keel can become a slug in the water and potentially dangerous, whereas if it was properly tested and refined before final fitting out, then it could and should become a delight for the owner.
A power boat with a badly placed motor may rise too high in the bow if the power thrust line is not applied correctly and simply become unstable with higher speeds and vice versa. This is often ameliorated by attachments in the stern, but may be a sign of poor design - or just another prat at the helm.
On some boats, the hull dynamics are modified with speed, where tail planes are used on powerboats to keep the hull almost level across waves, or racing yachts whose rear hulls are wide to maintain displacement at greater distance from the centreline, rather than induce higher angles of lean while also affecting the angle of attack to the wind. Other modifications include stabilisers on aircraft carriers and tilting keels on racing yachts.

The incredible range of waves that any hull must be expected to handle in the worst conditions, cannot be underestimated.

Ideal hull design in open seas will depend upon the power source and levels of fuel economy or the amount of sail needed to maintain headway.
For ocean use, all seas must be capable of braving, as the ability to run for a safe harbour is not always possible. Therefore the designer must always be responsible to make sure the design can handle whatever is possible, to the extent of including life rafts and such like, should the design be pushed beyond its capabilities. Many boats get pushed too far and never return.

Hull design will depend upon use.
I do not like the mass produced, white plastic ginpalaces which are perfectly good for the job of posing, but little else, pollute and drink fuel like it was water, and invariably annoy all the other boat owners around our coasts with their wake, excrement and condoms. Ginpalace boat designers could be far more ecologically sound, while still offering such follies in a modified form. But their greed for profits seem to come before any common sense or any ecological or social responsibility. There are better options for a better world and that goes for these designs too.

Many far more sensible power boats and motor boats have superb hulls for a long days cruising or fishing far out in the English channel and for a weeks motoring around our coasts, - and such boats do not upset others.

Yacht hull design is the oldest and also the cutting edge of options.
From the small one man and two man racing classes, through broad arsed racers and the more sedate, wide beamed fun cruisers, to the monsters of the round the world (now just around Antarctica) races.
Looking to all these hulls for inspiration is definitely a good starting point for sail.

The yacht is slowing evolving towards the broad arsed racing design simply because works so well. The ability for a leaning hull to displace the water such that it optimises its balance is always a good idea. The modern hull does this increasingly well and can do so with less keelage. If the hull, when leant over, realigns its centre of gravity relative to the centre of buoyancy to the upwind side, then the boat will tend to remain more upright. If the hull shape at this angle also induces straight line steering, even with such a sideways force, then all the better. Therefore yacht hulls are gradually becoming designed to be stable and balanced at optimum angles of lean, with the upright state merely a secondary consideration.

Most power boats have two types of hull.
The rounded bottom with curved ends, similar to a lifeboat you would find on a liner, where it is designed to take any seas in any angle, and preferably run with the waves. These roll rather well and are not there for comfort, rather than to stay more or less upright in all weathers. Such boats are designed for slow speeds where the engine is little more than a donkey engine chugging happily and lazily all day, and can often be found on smaller working boats and general purpose hulls for low speed steaming or motoring in coastal waters in all weathers.

The other hull is for power stabilised craft, where the forward motion is employed to assist stability, usually in milder seas. It may be noted, that a V hull may stay upright more in flat waters and less susceptible to roll in mild waves, while the round hull is less stable in mild seas. But - In rough seas the V hull also tries to remain level with the water with less roll, but when the wave is 45 degrees, the boat tends to follow. The rounded hull relies more on its ballast to remain upright rather than the shape of the hull and therefore when the wave reaches 45 degrees, the round hull is less affected.

It is not difficult to decide which hull shape a genteel day cruising yacht uses and which type of hull an ocean going yacht uses. For the worst situations, study the lifeboats of ocean going ships very carefully.

The more powerful hulls where the engine packs some punch, and capable of standing up to more than a few waves is commonly found with a V hull, where stability is improved by ploughing a channel through the water and from this, demands more power. Such V hulls are very common but demand that the boat has power to maintain itself in heavier seas, but has to run for home when the sea gets rough.
Whereas other hulls are at the mercy of the waves, but can often survive better with little or no power or sail.

The choice depends upon whether you want a slow, rolly boat which survives well, or put your faith in a reliable engine and stand up to a few more waves, then run for home, rather than to work with the mercy of the waves.
You could well be many hours from a safe harbour.

Most general purpose motor hull designs are a compromise for all occasions, to work well in good conditions, but must survive enough to get to a safe harbour when things get too rough.

A 'power boat' is not all-weather machine, they are usually 'toys', designed to go fast in good weather. Therefore modern motor boats are often V hulls, with power boats having a deeper V hull, because the owners rarely go to sea unless it's a nice day, or perhaps running drugs at night.

Moderate power boats, such as those for holiday coastal cruising have a mild V hull and with more than a modicum of power, can use the power to maintain their relationships to heavy seas and thereby be less at the mercy of swells and waves.
Round hulls tend not to fight the sea, but to work with the sea in a more passive manner. Found in traditional working boats and lifeboats of liners.
Most yachts can survive far better than motor boats.

When meeting a big wave, most boats hit it at about 35 degrees, as going head on will cause the bow to dive-in on the other side and cause more problems. By hitting the wave at an angle, the bow will tend to ride in a more level manner across the wave, allowing the hull to regain its stability on the other side of the wave. Wave tank testing is mentioned later.

Whichever boat you choose, you must still understand that the worst seas can be survived if designed correctly. This usually involves a self righting lifeboat, especially the fully enclosed versions found on North Sea oil rigs and which deploy down a chute into the sea. - The other option is to have a reliable engine or if not, then be more at the mercy of the sea, make sure you have a damn good liferaft and a well practised crew.
Few if any power boats are made today with round hulls.

A sensible all weather motor boat will often be twin engined, with moderate Vee hull and capable of tackling the waves head on and plenty of power in reserve. If a single engine, then an all weather boat must have a truly reliable engine with an impeccable maintenance regime.

(The V shaped hulls make for an excellent opportunity to make this form of hull from flat sheets curved to shape as mentioned later. This applies to both flared and knife bows.)

The picture shows some strong breakers, the power hull to cope and the need for truly reliable engines.

For yachts, a different hull is recommended for similar waves and never so close to the coast.

Stern design.
For many the stern is the place where the small boat is lowered to go to the pub beside the shore, or to get in and out for swimming. For others it is where a high rolling seas hit and if the buoyancy is well designed, will allow the boat to survive well, even enjoy a potentially dangerous roller coaster of a ride, without excessive forces pushing it down or up, but merely working with the waves.
Fair weather racing yachts tend to have squared sterns as they have little intention to remain static in high seas. Whereas more pragmatic ocean going yachts tend to have a more storm friendly stern. The same applies for powered working boats.

Bow design.
If a good-weather power boat, then it may not meet really high waves and the bow can be flared to spread the waves from the deck, or just have plenty of sunbathing space over a pretentious bow, but the flare is mainly to ensure the bow does not go too deep into the waves as it powers its way into the waves rather than roll with them, nor dive on the trough on the other side of the wave.
The vertical bow tends to cut through the waves and therefore tries to stay as upright as possible, usually with a furled main sail and good keel weight. This needs plenty of skilful rudder work to semi surf the hull in a reasonably safe manner while hoping for a good storm accessible harbour, while plenty of sea is shipping over the superstructure - and thus is most pronounced in sailing yachts. - This is when sailing really comes into its own.
A modern yacht will also have the bow just above the waterline so it can offer greater stabilising buoyancy into waves and also be more able to survive any floating debris such as logs, or large steel containers. hoping they will deflect before wiping out any arm and pod keel.

I consider the masters of power hull design are the R.N.L.I. whose crews take to the seas in the worst conditions. Looking at lifeboat design over the centuries will give the designer a fine starting point for a sensible hull design. The more I study their old and new designs, the more I learn.

Not all boats have to bob about on the waves.
Cutting through the waves is increasingly more effective with good design, be it power wave piercing hulls or even sail, such as the ill fated Team Philips, an excellent catamaran let down by lack of development funding and almost no time to get the design properly fettled before going to sea. Nevertheless, what this machine did, in the short periods when all was working incredibly well, was that it shows that the future of sail is far greater than anyone could dream of. It is still one of my favourite designs, simply because the design genuinely works, even if the manufacturing needed another two years to get perfect. (If only the main parts could have been salvaged and the structure rebuilt as part of the development process towards the perfect racing yacht.)

Cutting across the waves is also possible, such as the hydrofoil which needs lots of power, but always at the risk of an unwanted log or container, ready to rip off the hydrofoil legs, when a well flared bow will be useful.
A better alternative for calm, uncluttered waters is the Ekranoplan which is in effect part boat, but mostly aircraft, which uses the phenomenon of ground effect. The present Dr Lippish design is most surely the most advanced and most efficient of the many designs now coming to the fore, although the Russian military with their and eight jet engined 'Caspian Sea Monsters' have also shown another direction. Some of the smaller US designs have seemed to have totally failed to understand the fundamentals of this exceptional concept.

Submarine hull design can be efficient, but may need greater power, although it does allow a more stable platform. The composite design of an underwater buoyancy hull and power unit under the waves, with an upper platform above the waves has been tried on many occasions. Variations of this concept with massive semi submerged catamaran designs has proven most effective such as for some high speed car ferries. There is nothing to prevent a single submerged hull, but stability becomes a major design problem unless designed well, preferably with adaptive ballasting and bomb proof stabilisers. See appendix.

The hull must be able to handle the worst seas.
The boat shows must always be scrutinised, because what may look good in the show, may not handle so well on the open sea. So always be incredibly critical and study the promo videos and talk to owners, then check if they actually have used the boat in worst conditions, and always compare with many others.
Ask what tank testing has been done on the hulls, the stabilty graph, and the fuel consumption as a general guide to hull efficiency for cruising.
If offered a test run, then always ask to ring back, then check the weather forecast to book the test on a bad day !
If they don't want to take the boat out on a bad day, then it's probably crap.

It is assumed the hull design of most boats is not important on calm seas at low speeds, as manoeuvring back into harbour from open seas is comparatively safe. It is when the seas get difficult that hull design must be considered of paramount importance.

Always compare any hull with similarly sized working boats and their hulls, as real boats do not suffer fools gladly, often putting to sea in all but the worst weathers.

The basics of hull design is to keep friction with the water to a minimum, by deflecting it most efficiently, while also ensuring acceptable stability in the worst conditions. These two conditions do not always work against each other, as good hull design can improve efficiency with speed, such as the early studies in deep V hulls and also in 'planing', where the hull is encouraged to lift out of the water, thereby reducing drag.
The stepped hull of earlier racing boats further decreased drag and introducing an air barrier has also been tried. The stability of a fast boat can be superb if the hull makes use of the speed in the water. The V shaped hulls exhibit incredible straight line stability, but do not always make for good manoeuvring and can be a pain when at rest and when real waves appear. Done properly, a planing hull should make almost no wake, but may not be able to tackle anything stronger than baby waves.
Yachts are the masters of stabilty in all seas.

Bobbing about.
It is incredibly common for friends and family to enjoy a day out on a boat, - until you reach the waves. Whereupon they can be prone to sea sickness or just simply don't like the constant rolling of the boat. If you unfortunately tend towards being a bit of a 'boatie', then choosing a stable hull may be more important than an efficient hull.
(If just boating with friends on nice days, also consider a toilet as not everyone wants to consider the lesser options at sea. )
Yachts often stay at a lean angle for much of the day, so can reduce the bobbing effect, or at least mask it. When the wind drops but the waves remain with little manoeuvring ability and considering using the donkey engine when the wind fails to appear after an hour or so. Hopefully, you may well find yourself relaxing back with the forward gunwale awash and your feet on the opposite seat, or perhaps with your feet under a foot strap of a racing yacht or hanging off a trapeze in a dry suit or a steamer. This is proper sailing and is highly recommended if you love life.

If you truly enjoy sailing in most weathers, then choosing a suitable hull design from the outset will enable you to push the yacht far beyond that of most yachtsmen, and do so all year round. Always carry a mini liferaft and a ship to shore radio if pushing your limits and preferably a transponder or similar device.

Power boats or ginpalaces can power their way through waves, but this costs money in fuel and upsets everyone else by their wash, thereby such prats in power boats are never liked. Usually only in good weather, so they upset everyone.

When any powerboat or white plastic ginpalace is too inane or a yacht a little too exciting, - then getting a sensible 'day boat' which is stable and economical will reward the effort, but will depend upon your choice of hull design.
So if choosing a small day boat hull, check similar sized hulls and interrogate the builders at the boat shows for getting the nicest hull for a nice day out with friends and family if they are not born sailors.
Such day and weekend hulls are often evolved through decades of similar craft, to becoming very good all-rounders for many people and their families.

Choose your hull well.

Build your own. Some options.
The following will consider the small sail and power boat, capable of about two to four people (maybe six on a fine day and within two hours of harbour) as this is the range of boats most sensible people will want to build for themselves. Something in the range of a 15 to 35 footer, depending upon the moorings.

Sail hull design.

Making your own hull will depend upon the design you desire.
It is possible to buy bare fibreglass hulls and fit them out yourself or make a wooden or ferrocement hull. Making sure the mast and keel are accurately positioned, sized and weighted for the hull is paramount.
Making a hull from scratch is often more expensive in time, but can be cheaper to build, and allows you to take advantage of the latest trends in hull design and to make the perfect boat for your needs - if you get it right.

Many people buy a second hand boat as their first choice. This will give problems unless a really good choice, as second hand boats are often sold because they are in need of repair or need taking out of water for repainting and major maintenance. If you have the time and are keen, then this is a good apprenticeship for hull, rigging and engine skills.

We are not all racers. Many knowledgeable people buy a ready made bare hull, especially if it's their first build after five years or so with a second hand boat. This ensures the boat is made to their own specifications and needs. With some reasonable skill, a ready made hull can offer a boat far better than any 'off the shelf' design and at lower cost.

If a radical design, then it is often a good idea to make a one man scale yacht, then sail this for a season to get the design, hull profile and balance right, as this is much easier and cheaper to do before scaling up. Making different sails for this need only take an evening. A simple one-man rig like this will show up far more problems than a larger one, as it is more susceptible to smaller waves and therefore more easily developed to react as needed. The only problem is that the owner is comparatively heavier than the full size yacht, and relative ballasting may be needed for a small crew in the full scale design.
Being able to thrash a small test hull around, then add some extra shape or buoyancy or shift the centre of gravity, the position of the mast or add wide-arsed 'wings' to the sides, or reshape the nose to cut through waves as part of development can be far more fun than simply playing with a ready made hull. Applying some semi rigid builders foam sheet to the basic hull then shaping and coating with a thin layer of filler and testing again can lead to a very nicely and refined racing hull suited to your needs or sailing style. Likewise, modifying sail designs can be much less expensive and allow faster development with small test rigs. The ability to replace the sail with an airfoil can also give insights as to what is possible. What works on paper and what actually works in the real world.

If you get the chance to watch a Moth class race, do so, as this class uses sail and hydrofoils - a truly wonderful combination.

Sailing cat design has evolved from two identical hulls into two symmetrical hulls. Superstructure design has given way to the advantages of open access yacht design, with the lightweight and balance advantages of dual hulls, but also allow stronger, lighter rigs to be developed. The development of moving the hulls parallel to each other to offset the mast thrust line is also being developed and even offers elimination of the rudder in high speed racing. The simple yet radical leap of simply fitting nylon mesh rather than decking shows how development has moved towards lighter, more flexible and inherently safer designs for safer, cleaner and faster sailing.
I will not consider power cats, as the need for dual props or outboards on steroids is not eco friendly unless a large designs such as high speed ferries. Small cats with a single prop are not uncommon, but mainly for very stable dinghy designs with putt-putt outboards.

Yachts keels are available in many designs.
The simplest is a removable plywood central sheet, or dagger board of a Mirror dinghy where the keel is merely to keep the boat from Sway to port or starboard, to maintain stability in the forward plane. This keel has no weight, so the yachtsman has to lean outboard to counteract the effect of the wind. The yacht can be sailed right up to the beach if the keel plate folds backwards or if a vertical dagger board design is lifted in time.
The cruising keel of a day boat may be part of the keel as a deep keel line, where the hull blends smoothly down to the weight at the bottom of the deep hull, and is often found on older styles of yachts. This type of keel has the problem of being fixed and prevents a yacht from reaching the beach unless using side supports at high tide and so demands a reasonably deep mooring.

Some modern day yachts use twin keels of a short, stubby form, which allows the yacht to be high and dry and stable on the beach when the tide recedes and also allows zero water level low tide moorings. This is not such a compromise as it would seem if designed properly. When heeled over, one keel will maintain forwards stability, while the other, (being further out than a central keel) will effectively help to offset the effect of the wind. It is the effective mass of the combined keels which counts, plus the overall hydrodynamic effects. The use of two such keels will need the rudder to have a similarly deep skeg to give the third ground rest, so the hull can remain securely upright on three legs.

The modern racing keel is a deep vertical arm with a single smooth weight as far under the keel as possible and this has the advantage of minimal drag with minimal mass placed at its most effective (static) point. Such keel designs have absolutely no intention of counteracting sway, leaving this to the shape of the tilted hull design.
The 'weight on a stick design' of keel also has the advantages of being able to be lifted for shallow waters with minimal sail.
If making your own 'weight on a stick' design, and using a thin arm with hydrodynamic section, then making it liftable or at least deflectable is recommended, especially if an ocean yacht and you don't want to hurt a whale or scratch someone's submarine. More on keels later.

I have met many people who have paid stupid amounts of money to buy a standard yacht (bike, car, computer etc) and resolutely refuse to try even minor modifications or adapt it to their needs (sailing, riding, driving style) or to take advantages of modern developments, for fear of doing something different: Woosies.
By building your own, you are always modifying and developing, and perhaps even a full redesign over winter, - it can only get better and end up far nicer, to evolve into the perfect object of desire for you.
Do not become a 'void if modified' woosie.

Catamarans.
Cats are not in the Olympics - boo hiss. Call the RYA now.
Catamarans do not use keels as the upwind hull automatically becomes the counterbalance to the wind force.
I like cats. The best two designs ever, have to be the dual kayak central joining used by Arctic explorers of the north west passage, where the hulls became separate sledges. A superb design which allows snow and ice walking, and yet still gave a reliable and stable means of crossing the most dangerous waters on earth. The other cat is of course, Team Philips which has shown the world where modern sail design should be going.
I used to test my first toy catamarans with my own designs of rigid vertical airfoils at the age of twelve and am still looking for better designs in all forms of boats both single and dual hull, as this is where the true fun lies for those who can build, rather than those with money and no sense of innovation.

Evolution and innovation.
There have even been pedal powered hydrofoils. - Never be afraid to experiment.

In a Britain choked to death with paperwork, our roads deliberately clogged with political correctness gone mad, and many Brits are gradually veering from road vehicle design to boat design, simply because Britain is clogged with paperwork and thereby killing off its design future.
Britain still has the best designers, but they have to go abroad to work. Britain still is now a design dead end.
Britain has not designed a genuinely radical car for over thirty years, the last being the real Mini.
Many of the better British designers now leave Britain in droves, and quite rightly too. Britain is now so corrupt and badly mis-managed, grossly over-taxed and heavily 'paperworked', to wantonly stifle innovation. Shake-hand-gangs rule and ruin Britain and grab our taxes. Kids leave schools able to pass exams, but unable to talk clearly, nor read nor innovate. Don't blame the kids. Virgin buys high speed tilting trains from Italy, when Britain should have been selling tilting trains to the world for over twenty years. The once proud Royal Navy now suffers the indignity of our aircraft carriers being built by the French. Parliament is a sick joke, never worth our taxes and should be fully ashamed of this mess.

If you should have a mind of your own, (rather than political correctness) then taking any new design to sea is wonderful and far more exciting than merely the same old sailing day out. There will be more surprises, some bad, some good - and as you learn more, then the surprises will increase predominantly towards the good ones.

DIY: Do it yourself.

If you have no garden, have the hull delivered to a dry mooring or beaching as you fit the propeller shaft and sea fittings, (and of course a bilge pump and a charged battery). Then roll it down at low water, check for leaks at high tide, then pootle it to your mooring at slack tide and fully cover with a tarpaulin. Put all your heavy items in the hull before leaving the shore, or be prepared to motor alongside to pick up the heavy stuff. Always keep the mast safe until fitted, as they can cost a fortune.

Making a hull from scratch is often more expensive, but allows the builder to take advantage of the latest trends in hull design.

Hulls are available in a wide range of designs, from hobby boats, through small fishing hulls and such like, through small fun power day trip hulls with an outboard motor, to larger motor boats and daft gin palaces.

If designing your own hull, then it's best to start with a known good design and work from there. In many cases, it is just a scale up or down a little from a good standard hull while still retaining the characteristics of the original design. Change the scale too far and you may come across increasing problems.

A boat displaces water to the same mass as the boat, so a two ton boat displaces two tons of water. It is how the hull displaces the water that counts, and more importantly how it displaces the water as it moves forward.
Just moving a hull forward through the water is living in an idea world, but boats lives in seas, where they are always susceptible to far more variables and the attendant forces.

If designing your own hull then you will need at least to consider (if not doing) hydrodynamic studies. For home test tank testing, See appendix 1.

The hull will be exerted to many forces, and these react in the six planes. (3 planes, 3 axes.)
Vertical up and down called HEAVE.
Fore and aft tilting called PITCH.
The twisting about a vertical plane known as YAW, as affected by rudders.
The forward motion called SURGE, which is susceptible to drag.
The axial rotation called ROLL, most commonly known by all who have used a boat, even on a mill pond.
And SWAY, which is being pushed sideways, most common with yachts or with side winds.

With all these forces and a centre of gravity relative to the waterline, and the change in displacement under the waterline, (a hull is rarely a constant shape from fore to aft) then a vessel exhibits different responses according the shape of the hull and the speed at which it travels over the constantly variable water surface.
The hull shapes of a tanker, a yacht and a moderate power boat, each of which have different masses, hull shapes, keel weights, therefore display different reactions to the forces acting upon them.

Any hull displaces water and the water naturally induces pressure on the hull the deeper the hull penetrates. With waterpressure, the hull is tended to deform greater near the keel. In practice the average small hull need not take notice of pressure with depth, not even the Geodeseic Airolight. In practice a hull must handle much more pressure than this in open seas and displacement forces are usually ignored other than to calculate the static displacement waterline.

A long thin boat such as a tanker, which may meet a wave the same length or pitch as the ships length, will tend to bend in the middle, but with a travelling bending force as the wave travels along the ship, this causes constant structural stresses. When the ends are out of the water, it is called hogging, and when the middle of the ship in the trough it is called sagging.
Racking is a deformation caused by a ship rolling in beam sea, where the ship lies parallel to the line of the wave. - Looking at the cross section of the hull, it is prone to deform like a trapezium if it were not for the bulkheads.
The sides of some hull designs may veer inwards slightly, called by the wonderful term Tumble Home which allows the boat to moor close and still manage some roll, but is usually only for larger ships. Tumble home was supposed to assist the metacentre of gravity of sailing ships but modern designs have to some extent superseded this. As this monograph is only interested in smaller craft then these are not considered here, merely to note that such forces exist.

All decks have camber, which allows free water to run off cleanly. The angle or curvature of the camber need only be slight as there is usually to be any standing stagnant water on a boat unless moored on a mill pond with no wind. Standard camber on ships of one fiftieth of the breath of the hull.
Flare or flam is the flaring outwards at the upper deck forwards of the ship to deflect waves and is most pronounced in power boats, frigates and modern liners. This can help bring the bow up into the wave and if designed and tested correctly, can improve the dynamic balance of the hull in heavy seas.

At rest in water, a boat can have three possible states of equilibrium.
If the vessel is disturbed and returns to its original state, then it is said to be in Stable Equilibrium.
If the vessel is disturbed and remains in its new state, then it is said to be in Neutral Equilibrium.
If the vessel is disturbed and continues along the path, it is said to be in Unstable Equilibrium.

An example is in roll, where the vessel is disturbed and tends to return to its upright position displaying stable equilibrium.
An example is a tree log in a river, when rolled, would tend to continue to roll other than the effect of friction, so the log will remain in unstable equilibrium.

A standard hull in still water will displace the water until it is in stable equilibrium, and all being well will be upright, indicating that the centre of stability is on the centre line of the hull directly over the geometric centre of the displaced water and the centre of gravity of the boat. If a person now steps on board and stays to one side, then the boat will roll to a new stable position as the centre of stability moves over to the new geometric centre of the displaced water / shape of the hull.
If the person or new load is to the rear or to forward, then there will also be a change in pitch. The change in angle of the hull to the water line will change until the boat reaches a new state of equilibrium.
If the effective position of the load is gradually raised relative to the deck, the hull may remain upright if the load is perfectly central, but eventually the hull will no longer retain a stable position and will turn turtle. (Or perchance allow a load to slip off the deck and thence return to a stable position).
It is the shape of the hull and the way the water is displaced which will determine how much a boat will change to a new state of stable equilibrium. A catamaran will lean less, while a deep chine boat may well lean more until the larger zone of buoyancy area comes into play.
As the centre of gravity is raised further, the boat will eventually reach a state where it becomes unstable. A dangerous condition is when the centre of gravity is raised, whereupon the force acting to return the boat to a stable position will be less, and so the boat will tend to roll badly, even with heavy ballast. It is for this reason that tall liners use aluminium for the upper decks and why flying bridges on small boats is a stupid idea. (The only acceptable reason for a tall part of the superstructure is on day fishing boats is needing a good, deeper view in clear waters, or rescue vessels where a high viewpoint is needed to scan the wider horizon for signs of survivors.)

With boats using a waterline where the stern is similar to the bow waterline, then the centre of flotation is usually mid point along the centre of the waterline. On small boats where the waterline is tapered towards the bow with a wider stern, then the centre of gravity is above this Centre of Floatation, which will be abaft the middle point of the waterline, often quite far back from the middle of the waterline for a power boat. With such an irregular area of floatation, then adding one pound mass to the rear may change the waterline by little, whereas adding a pound mass to the front can change the trim far more, as the displacement area forward in the hull is far less. Therefore the centre of gravity and the distance fore to aft of any mass must be carefully considered to adjust the trim of the boat.
In a planing hull, the centre of floatation is dynamic according to speed and gradually veers towards the rear of the craft as speed increases, but the centre of gravity being constant, then stability of the craft must be carefully designed and tested. In some powerboats, where there are steps or pressure traps, the air pressure underneath may also act as part of the area of floatation if it supports the hull.

With yachts, a shallower hull may well be less effective to windward, but handle and tack easier, to put less strain on the structure.

When designing a hull, three views are normally given:
The side view or Profile.
The plan (half breadth plan) looking down including keel lines and proposed water lines, and lateral lines (waterlines) above and below at equidistant levels.
The third view, a fore/ aft view, Body Plan, showing the various cross sections working form fore to aft of the hull.
The later two drawings need only show half the ship as it is assumed to be symmetrical.
Common consent uses just eleven vertical sections for small craft, with number 1 section at the stern on mercantile craft. (No 1 section at the bow on Admiralty drawings.)

Other lines of concern are called Buttocks, where the line of the hull as seen from the side, usually at the quarter breadth of the hull but other buttocks are common. These show the gentle curve for optimising wetted area and water flow. A modern yacht has a very low, gentle buttock line, whereas a motor cruiser will be more pronounced, as it is not after such speed nor clean waterflow efficiency as for a racing yacht.

(For wooden and ferrocement hulls, the fore and aft body plan sections are often copied full size onto the floor to make up direct wooden or steel trusses to ensure a very accurate hull.)

When drawing, the intended waterline is the reference point for all other constructions.
As the design develops either through maths or model testing, then CG centre of gravity and CB centre of buoyancy can begin to find their reasonable positions on the drawing.
The centre of buoyancy is initially assessed by counting up all the full boxes and half boxes displaced and finding the mean position fore and aft.
The centre of gravity is initially assessed by positioning the relative masses of the engine, mast, and dividing up the hull masses and then calculating moments about the end points of the waterline to give a basic working centre of gravity. Another method is to make a cardboard profile and suspend it from two different pin points, each giving a different vertical line, and where they meet should be a rough C of G. This can be improved with greater sophistication using more card or even a card model of the hull, although a two dimensional representation is often good enough.
This is also a good time to use the same CG data to work out the polar moment of inertia about the pitch angle.
When the centre of buoyancy is initially assessed, then the righting mass for a keel can also be calculated using the CG and CB points.
For yachts, (and cargo ships with poorly distributed load) the metacentre of the craft is also very important, where the GB and CG where the shift in lean angle changes the stability of the craft. As yachts are often heeled over, this becomes of greater interest to the point where the lean profile of the hull is calculated as the working design rather than as a temporary, unstable position in the water, but as a working stable form.
As may be seen, the chances for errors or at least indistinctive factors creeping into a design is all too prevalent. This is where a good designer knows what to look for and to take account of and which to work around or to use empirical or highly developed knowledge and skill in the design processes.
Therefore making models is also important. Models are not only for testing buoyancy lines and stability, but also to later check the dynamic effects of the hull design. See also ballasting and hydro tanks in appendix.

When a final design of yacht hull is modelled and chosen, it can the be used to pinpoint the mast position and then highlight the ways the forces of the mast and rigging will be resolved into he hull prior to final structural design work. The positions of bulkheads stay and shroud mountings and such like can then be integrated into making a potentially far lighter and stronger hull design. Consider it as if designing a corset or a suspension bridge, or a Barcelona cathedral - lots of components pulling, pushing and shearing in different places, all to be resolved smoothly and with a balanced harmony. (See also: 'Arches never sleep'. O.U.)

Modelling power boats will allow the optimum position for the propeller or other driving device and placement of the engine as a heavy mass in the hull for stability, strength in high seas and general hull response.

Where the rear of the hull is unusual, then a ghost transom can be added to the drawing for accurate alignment of the waterlines rather than mess about with awkward angles, especially when copying the drawing to models for testing.
Hydrostatics and stability are still the main aspects of hull design, which are becoming more scientific in study as the data builds up and testing techniques are developed. Computers are gradually taking over the more professional side, but always remember that what may seem good on paper or as computer data, must always be backed up with real testing to prove the data is valid. I remember using the gangly arms of a planimeter for this stuff long ago, but nowadays rarely use such tools, but they still remain perfectly acceptable if they are kept in good condition and used on a good, horizontal drawing board. (My monograph on design, technical drawing, 3D graphics and animation may be put on my website if sufficient requests.)
Theory is never perfect and testing is never ideal.
I choose testing on the water every time as the final arbiter of any design.

If a beginner, then designing your own hull is best left to experts, or to copy an existing known good design and scaling it slightly if needed. Perhaps you like a certain design, which is a little too big or too small for your liking and wish to scale it to suit the maximum waterline for your mooring, or of an awkward mooring perhaps including a retractable bow post to a yacht. Do not scale too far as there are many problems such as some delamination or microcracking factors may change with the stresses on a larger scale if using similar weights of materials.

Building your own.

Whatever design you choose, they all start with a basic bare hull. - Usually a fibreglass moulding with a few internal supporting ribs.
The rest is up to you.

Having made your choice of hull after a season of watching and hiring similar craft and chatting to knowledgeable owners, then the build can begin.
From your studies of similar craft, you will have made many notes and photos of the way it lies in the water and thereby be able to draw an optimum waterline of the best handling versions of such craft.
Also discerned will be a good working idea of where the centre of gravity should be, and appreciate the probable position of the effective ballast.
It is important to get the waterline marked, as this will affect the overall handling and will require careful work towards getting the hull to sit in the water in the best manner.
If a power boat, then you will have also studied the way the hull may or may not be expected to rise in the water under power, have noted this on similar craft and marked this on the hull too, for future reference and fettling with later sea trials. Perhaps you have decided upon the semi double hull with air dam in the middle and how this also supports the hull partially out of the water at speed.

The most important consideration is how the hull lies in the water in all conditions and noting the stability of various types and looking at the hull below waterline. When comparing, use sea marks as your reference guide, rather than painted waterlines to see which are the better choices of hulls. Those whose hulls sit at variance to any painted lines should be studied to see where they may be amiss.

For a few days, or when on holiday, sit on a shore with binoculars, or a video with high zoom and a tripod to look at the side of a yacht or power boat to see how it lifts its bow when meeting a wave. If most of the mass was very near the centre of gravity, then it will tend to rotate about this point easily. If the mass is spread fore and aft of the centre of gravity, then the boat will tend towards remaining more level in relation the wave. Too much or too little 'dumb-bell effect' will cause the boat to react poorly.
A poorly designed boat will bob about too easily and a stable boat will pitch and roll less. This should not be confused with a stable boat with a round hull, as stability is only partially controlled by keel mass but also by effective displacement in relation to this centre of gravity and the angle and force of the wave.
The position about which it pitches will give an appreciation of the centre of gravity.
So when noticing any boat, estimate its centre of floatation and the centre of gravity, then note the hull shape and thereby consider how it behaves in relationship to various waves compared to other boats.
Just by studying videos, you can guess the centre of floatation, work out the centre of gravity, and a reasonable working guess as to its dumbbell effect, (polar moment of inertia about the pitch and roll planes.) Get a feel for the hard working hull.

If making your own copy or variation of a desired hull, or if a radical design, then it is often a good idea to make a scale hull and test this to get the design and balance right, as this is much easier and cheaper to do before scaling up. A simple model boat made in blue foam with a sail or motor is easy and cheap compared to the work ahead. If a model displays good handling, this can be followed by a single man hull before building a massive boat.
The piccie shows an ocean racer test rig entering a test tank. This 'model' is about six foot long, and just about good enough for a real yacht. If it was scaled up 30 percent, then it is much easier to make a real baby yacht and sail it for real tests.
If you don't have a test tank, then it can be pulled towards a still mooring with a cord to do real tests rather than in a tank. If the model is to be modified, then so can a 'baby ocean yacht'.
Small test hulls will show up far more problems than a larger one, as they are more susceptible to smaller waves and therefore more easily developed, modified then refined.
Even moving the mast back or forth just a few inches can give excellent insights to how the craft behaves and improve overall handling no end.
Being able to add or make a temporary wave piercing or wave cutting bow is easy with models and small test craft, especially during winter when the waves are most exciting. Always add a spray deck or bow deflector to prevent swamping with any wave piercing hull.

Whether sail or motor, you could make model radio control hull or comparative hulls of your final choices. Make a selection of radical hulls and compare them. They can be simply carved using blue foam, given a coating of car body filler then tested and more importantly, compared in all conditions. A few hulls to take a standard sail or simple cheap electric buggy motors and props and such like can be carried in any small car, then tested almost anywhere at any time and ballast changed to study the effects. If a local boating pond, with no one else is around, you can also make your own waves using a wide sheet of plywood and set the hull up to assess the angle of the waves relative to the course or wind direction. By noting the way the craft behaves with too little or too much ballast will allow the designer to know when things are getting too dangerous during full size sea trials.

Choosing a reasonable sail or power hull is comparatively easy as even a poor choice is not going to be a bad experience unless you get most things wrong. Nevertheless, any choice must be carefully done to ensure good safety.
Choosing or modifying or even designing a perfect or radical hull can be very difficult - unless you accept the present, often comparatively boring designs, but the standard hull designs usually work very well.

Having decided upon a design of hull, the builder can now choose from a variety of materials and manufacturing techniques with which to build their craft.

Materials and manufacturing options.

Wood.

Today, the boat builder has a wide range of superb woods at their fingertips.
The best modern wood is marine plywood with its cross layered strength with lightness and inherent waterproofing. To this can be added modern jig saws and a wide range of adhesives to offer almost unlimited shapes and sizes and to do so incredibly easily.
It's not just cupboards which can come in flat packs.

The traditional wood keel with ribs then planking is nowadays almost defunct simply due to its cost in time, skills and materials. Such methods also need plenty of special trees with interesting main branches which can be carved into naturally curved corner pieces and other shapes needed to make a strong hull. So getting this kind of wood is almost impossible, although the forestry commission have a few exceptional trees specially reserved for masts of replica ships and repair of national treasures.
A few boats are still being built using traditional methods such as replicas and Gigs for traditional racing teams of oarsmen of villages around the world with up to 130 Gigs competing on some occasions.

The simplest wooden craft is the handful of pre shaped plywood sheets (BS1088) which allow slight curvature and then stitched together with wire, to get a nicely curved hull. The stitching is then protected with extra strips of wood and fully waterproofed. The flat sheets are often formed to curved shapes with just a flat transom plate and a pram type front plate, to make a minimalist sail boat or for a small outboard motor.
The later versions of this concept has been into forty foot, round the world yachts made with pre-formed and self jigging steel plates. The basic design technology is the same, just on a massive scale.
The reader can design their own pram or ocean going vessel with some cardboard from a breakfast cereal, a pencil, scissors and a keen eye for lines. Then hairspray or lacquer the cardboard and run initial ballast and stability tests in the bath. (This is one of many school technology projects I've developed over the years - I've a B.Ed and a B.Sc - gizzajob.)

The real problem is making up the large curved shapes which will fit neatly together for the ideal hull and this is done with cardboard at first, making a half hull and laying it beside a mirror to assess initial form. Then scaling up in plywood for up to 20 footers and if making a large steel hull, then scaling up the accuracy of a test hull for initial sea trials and testing before committing to a massive steel structure.
The picture shows the bulkhead self aligning lugs sticking through the aligned holes in the side plates, using tapered wedges to pull the bulkhead lugs up tight against the side plates to ensure a perfect fit prior to final assembly. In wooden hulls, the assembly can be by sewing with stainless steel wire and screwed and glued chamfered corner plates, plus the blocks and corner pieces of bulkheads.
With a handful of wedges, the hull can be assembled so easily and is self aligning. A selection of hull patterns can allow sheets of marine plywood to easily become ready for the water in minimal time. It's not unlike a sewing pattern, but far easier to assemble.
After assembly the alignment lugs are ground off and sealed. The keel is made by a V shaped protecting and joining strip or plank glued and screwed into place over the sewn keel join to make a very strong structure. In some cases, the keel strip can also be sewn as part of the keel join, so the adhesive and hull plates all pull snugly together for a very strong design.

(Please note: The lugs sticking out in the picture are far larger than would be actually used and only for illustration. Smallest lugs possible would be used to ensure maximum strength to the side plates, as the jigging lugs need only hold it together just enough for alignment and assembly. In most cases a lug half an inch or so wide would be acceptable for steel and for plywood. Anything larger than needed would simply compromise the integrity of the side plates. For maximum strength then just a screw hole for plywood and a threaded L clamp for steel. On anything larger than a dinghy, there would also be ribs and stringers, also jig cut and easily assembled before the outer plates.)

Further strength can be with gunwales from strips inside and outside of the top edge, and internal blocks screwed and glued where needed for hatches and seats, then buoyancy areas made in scraps of plywood for seats and internal supports then injected with builders wall insulation foam for emergency buoyancy.
Wood blocks or boxes can be glued and screwed to the rear, then carved out to allow double small wheels for rolling to the slipway and simple handles at the other end. - It's your design, have fun, so if you need a new pram or dinghy - then have a go, it's not rocket science and it costs little.

Here is a typical home build yacht, with simple manufacturing in marine plywood. Although small and only one to two persons, it has sailed around England. Note also the oars for use as a rowing boat when becalmed. A well thought out design which also has a deep, thin folding keel.

For larger wooden boats it is traditional to build up the keel, then add the ribs and then the outer planking, followed by many days of arm - aching caulking. This traditional boat building method best left to experts or if building a Windermere steamer or pinnace. See also steam engine monograph on this website.

If you hate the stickiness and smell of fibreglass, or do not have the skills, drills, planes, saws, spokeshaves, chisels and a keen eye needed for a traditional rib and plank hull, then this plywood method is a great way to make a cheap pram to get to and from your mooring and help develop your techniques for a larger hull. See also ferro cement.

GRP. Glass reinforced plastic.

GRP is essentially fine strands of glass fibre, developed in the fifties and used in many forms of cloth and tape for use with various types of resins. The resins are easy to work with and set hard. But such resins when un-reinforced, will shatter as they may be hard, but are not strong. To overcome this, the millions of fine strands of glass give the structure strength to the rigidity to make a truly strong composite. Glass mat is available in shredded mat, cloth and in various weaves and weights.
Apart from the mould, the biggest problem with GRP is that the resin is sticky, smelly and the glass too, is an irritant. You will need a full disposable plastic boiler suit or a few disposable cloth overalls and some cheap welly boots and plenty of disposable gloves, also plenty of disposable stiff paint brushes and rollers. When making superstructures, then a hat with a brim is also recommended.
Always make a test patch in the mould, to check it will release, so about a square metre over an awkward shape is best, and from this, the application technique can be assessed and modified before attempting the hull properly. The test patch should lift off fairly easily from the release layer, with a perfect finish.
If using a commercial female mould, then this is first polished and many layers of release wax burnished into the mould and the polished, then the first outer later or 'gel coat' which is pigmented for the outer colour is applied and this, having no glass makes for the smooth outer layer of the hull. Then a scrim layer to prevent the rougher fibres showing through the gel coat, and then the internal layers are laid up, by painting on the premixed resin and hardener catalyst, with the corners built up, then the main flat layers built and then the corners again, and then the flat layers, so a strong hull thickness is made. The glass must be stippled or rolled into place, so any excess resin is expressed from the dense layers of glass and where excess resin is to be found, this best soaked up with more layers of glass for elsewhere rather than allow hard chunks of unwanted resin which may need to be ground off later. There will be plenty of stippling around any difficult shapes first, and small and large rollers used to ensure the resin and glass are perfectly integral, with no air gaps nor any dry glass fibre areas.
For greater strength, woven glass fibre mat can be used, but it is perfectly acceptable to use the cheaper chopped mat, but more of course would be needed. For some areas, aramid cord, tape or woven sheet may be added, especially where a damaged hull must not be breached.
I prefer aramid cloth below the waterline, especially where the hull may be smashed about or damaged on rocks. At least along the keel and chine. It's simply cheap insurance.
If using carbon fibre cloth then you may well wish to use just epoxy resin and no gel coat, so the fabric technology can be appreciated.
If laying up your own mould, then you may wish to add removable fittings such as window panels and water inlet and recessed fittings into the mould, with the fittings covered in food cling film, or heavily waxed, so the hull layers can perfectly mould around them with total integrity - but always able to be removed from the mould.
If using a commercial mould, you may be able to specify minor changes, but this is rare, as almost everyone simply starts with a standard bare hull. For example, if changing from a single prop to a dual prop, then the main mould can be given temporary foam plastic tunnel insert cores without damaging the main mould, with the central prop tunnel modified after the core hull has been removed from the mould.
To help release a mould, it is worthwhile making a couple of inlets covered with thin plastic film during the waxing phase, so that air or water can be pumped between the mould and hull, using a foot pump in a bowl of water to help release the moulding.

If a special gel coat colour, then always make up more gel coat pigmented resin than needed, so the excess can be stored in sealed tins for superstructures or for later repairs with a perfect match.

When laying up in cosmetic areas, it is possible to ignore the glass and use sheets of various patterned cloth to finalise the outer layers, using a clear resin to match something strange. This can be applied to decking for cosmetic reasons, such as expensive carbon fibre sheet to give the false effect of a much more expensive hull than it really is. Likewise, if wanting the boats name on the side or wherever, then this too can be printed or sewn or embroidered, then applied to the side of the hull or cabin after a clear gel coat.
I prefer to embroider my frame numbers into the outer layer of carbon cloth when building advanced designs, as it makes identification harder to remove. I also recommended including an interogatable electronic data tags as used for motorcycles and such like, ensuring they are included in the fibreglass layering process and are invisible other than to those with identification sensors. Putting them in bow and stern, you can easily detect any stolen craft by walking alongside with a scanner.
The point to note is that although glass fibre is the best option in both cost and strength, there are oh so many variations on this theme.

If buying a commercial blank hull, then many changes may be needed, usually to fit differing engine arrangements and cabin arrangements. Perhaps your hull is designed for one engine and you wish to have two smaller engines and rudders or vice versa. Also the primary details such as sea water cooling inlets or fancy side windows, and of course any specific bulkheads and superstructure support beams for a custom design.
Sometimes the hull may be the perfect sea going profile, but you wish to change from a stern or Z drive with forward wheelhouse, to a mid engined layout with stern wheelhouse to maintain best balance. The bare hull allows almost any option.

A bare hull is indeed that - a bare hull - a blank sheet upon which to create a masterpiece.

Moulds.
The problem with making anything in GRP is to make a mould.
Mould making is where much work is needed. If making a basic catamaran, then only one, comparatively small mould may only be needed. For larger boats, then hiring a mould is possible but it is far easier to buy the hull already made. They don't cost too much and are usually considered very cost effective, and by asking around, you can research and find some really good handling hull profiles.

If making a mould, then a great deal of effort is needed and such effort is only viable if making a specialist racing hull, and even these are rare.
Almost all other bare hulls are commercially available, and even having a bare hull transported from Canada is nearly always cheaper and easier than making your own. (I'd trust a Canadian or Norwegian hull more than any 'Mediterranean' hull, as they are designed for far worse weather.)
If your own design of hull turns out to be a winner, then this can be used to make a direct mould from the boat, then identical hulls made for others. Likewise, if a particularly old, but favourite wooden is hull ready for the breakers, then this too can be used to make a mould before it dies, plus of course, all the old fittings, sails, engine etc. Always take the chance to first permanently mark the waterline so the new design can be ballasted identically.

If needing a specialist hull, but cannot afford the time or money to make a proper mould, then it possible to carve your custom hull profile. An upside down internal mould 'plug' is made, then layer up the fibreglass layers of the hull over this foam. - To do this, set up some concrete paving blocks in the garden which are perfectly horizontal, then the keel line should be cut in plywood and mounted perfectly central and vertical, with the ground surface acing as a horizontal plane, so all templates will be perfectly aligned when making the final shape to this keel profile. Scrap wood, cardboard boxes or old palettes are built up to make the basic core, which will not move, and onto this is glued lots of white or blue foam using old bathroom sealant. White foam is far cheaper and can be easily sanded to shape, although it makes a great mess, and many hours with the vacuum cleaner will be needed. Once the basic shape is made, it is refined with plenty of plaster of Paris. Then use plywood templates to ensure symmetry along the centreline.
(Hot wire cutters are simply made from an old electric fire wire stretched across a bamboo bow and heated by a battery charger. To make your own hot wire cutter to shape white foam, see my composite frame webpage. The profile of the foam is laid out with strips of wood nailed lightly into the foam so the hot wire cutter can carve the foam between the wood profile and the keel to get the basic shape on both sides. More details on my web page monograph on composite design.)

If wanting internal strengtheners, sea water cooling inlets, scuppers, ducted prop shaft tunnels etc. to be part of the initial hull structure, rather than to add them later, then they can be carved these into the shape first and apply the fibreglass to make the feature, then smooth them to the blank hull shape prior to laying up the main hull.

Ideally the hull should be one thick coat of resin and many, variable thickness layers of glass so that the built up layers are bonded together at a molecular level, otherwise you may have to wait a day or two before sanding down to remove waxy surfaces, then apply clean other layers to finally get a smooth finish.
Tip : Applying plenty of layers in one go, to gain maximum strength does not lend itself to a smooth hull, so be prepared and get lots of thick clear polythene and plenty of large sheets of smooth, un-creased cardboard to press against the setting GRP to get the smoothest curves before it sets before the gel stage. Done sensibly, this also squeezes out any excess resin when making a lightweight racing hull. See also vacuum bagging in my companion monographs. Even a large home made hull can be vacuum bagged.
The final layers are cosmetic and ensure the hull is smooth as required prior to painting or with a gel coat.

Once a GRP hull is made or purchased, it will most importantly need a well positioned engine or mast.

Careful thought about how to build up the internal support structure will take time.
Internal structure will depend upon how you want to design the superstructure. If a working boat with a forward wheelhouse, then the engine may be able to be placed under the rear working deck space to maintain balance. Crabbers often have a rear wheelhouse with a forward working space and a hydraulic winch. Day fishing boats usually have a forward cabin with plenty of space at the rear for deck chairs and lines, plus a toilet and bunks in the bow. Small yachts may simply need a small manoeuvring engine to get into harbour which can be placed almost anywhere. Powerboats will be built purely around the balance of hull, prop thrust line and engine mass.
If you have not finalised the mast position, then the hull should be made to allow for various mast and keel positions for assessments and fettling during sea trials before finishing the design.

A common method of building up the internal strengthening is to lay up primary strengthening ribs. These can easily be made by crafting cardboard formers into dummy beam hollows, but blue foam formers over which to mould the ribs and such like is far better. If very skilled, use aerosol builders foam, squirted into neat lines, then carved to shape. Foam is best done with cardboard shaped covered in food cling film and held in place with masking tape. GPR is then built up over the formers to give suitable reinforcement with good spreading of stress loads with minimal localised flexing, so the outer hull surface does not crack too much over the intervening decades.

The prop shaft is assembled and aligned relative to the engine position and to ensure a good propeller thrust line. Onto the initial ribs can be mounted the engine and such like. See propshafts in appendix.
The propeller must have at least half a prop diameter of water above it, so knowing the waterline of similar vessels, this is the starting point for positioning the prop, relative to the hull, then the sump clearance of the engine, and between these will lie an ideal straight line for the propeller shaft alignment.
The overall waterline balance of a lightweight powerboat will dictate the engine position and this in turn will dictate the positions of bulkheads and fire walls, which in turn dictates the sea water inlet, exhaust routing and fuel tanks.
For day boats and cruisers, the engine mass is less important and many engine arrangements are possible, from Z and stern drives, though reverse drives where the standard engine is above the prop with the shaft driving forward to a gearbox driving back under the stern, and of course, the classic mid mounted engine. Even the engines can differ, from the standard in-line four, but for narrow rear engines, then a flat four petrol or diesel is possible to maintain lower deck heights.

Likewise for yachts, the mast position and it's supports and stays, the keel supports and mountings and the boom restraining point.
There is nothing preventing the builder from making a mast mounting plate with evenly spaced bolt holes such that the keel can be moved fore and aft by one or more bolt holes should the handling be less then perfect. Being able to remove the keel, drill a pair of extra holes fore or aft, then move the keel mass by one bolt hole pitch is good planing for any new yacht design.
Where the mast is socketed, then it may be on the upper structure to allow plenty of room below, or socketed in or near the keel. The mast mountings too, can be variable along the centreline.
Where a mast is supported on the superstructure, then the underlying structure must be particularly strong. I prefer an integral and strong X brace across my mast bases, hidden as part of the roof line of the cabin, (or to be more precise, the roof line moulded to the main X frame), such that the mast forces are spread across the hull more evenly than often found in simpler designs. Into the main V frame are spreaders and careful positioning of bulkheads into the X frame such that the hull takes the force as evenly as possible with minimal distortion, which is particularly important in a super lightweight fibreglass (or alloy) hulls, as too much flexing over many years this can lead to cracking, osmosis (or breakage of the anodising) and eventual damage of the core hull materials.
For yachts, the fore and aft stays and the shroud mounts must be strongly integrated into the hull design to prevent undue flexing caused by these highly loaded points, especially the shrouds, but be carefully controlled by internal bulkheads, ribs, stringers and other features. I prefer to add aramid lines into the hull as part of the original moulding to strengthen my hulls so they last far longer than standard hulls which are prone to gradual strength reduction over decades.
Always try to eliminate or circumvent major problems from the outset.

The rest is fairly straight forward.

Fitting a deck to the hull will need cross bracing and these must be able to take any sail mast where fitted, and crew jumping around above deck, such as jumping onboard from a harbour wall. Wood beams are possible, especially if wanting to make a traditional wooden deck, but this may still need a hidden under layer of GRP support and waterproof later on which to build the (thinner) wooden decking. For ease of manufacture, some people make thin primary sheet of GRP on a flat floor, slightly larger then the fore and rear decks, then temporarily fit and curve as needed to the bare hull. Onto this removable core upper structure can be moulded thicker layers where needed and to build up internal mast supports and walkway supports, and fitted the details such as raised cabin sections, winch mountings and many other details before final fitting the deck to the hull. This allows both fore and aft sections to be better integrated into a stronger, lighter hull, especially the stern under-deck storage and floorways, where folk often jump onboard from the harbour wall and to ensure the bilge drains safely and fully.

Aramid, carbon fibre and structural foams.
GRP has recently gained a few friends to the glass reinforcement game. Initially carbon fibre and then lately aramid. Carbon fibre is immensely strong and light, but using it for lightness is totally wasted unless the excess resin is removed. This is done by vacuum bagging - seen my monograph on carbon frames on this website.

I use a lot of aramid simply because it's cost effective. Aramid, most commonly known by the trade name Kevlar (tm), and is immensely strong in tensile strength. This makes it excellent for stopping chainsaws and bullet proof vests and so is often to be found in safety clothing.
Aramid is also useful for strengthening hulls, especially lightweight designs.
Adding a layer of aramid to a composite mast may not stop it collapsing under compression, but it greatly improves its tensile component.
I use aramid with my own special coating to make ultra-light-weight support cords for many purposes and are wound many times about eyelets to make semi rigid, lightweight yet immensely strong ties. See also sails.
Another advantage of aramid, in its woven cloth form, is in making a hull damage resistant, - especially if expecting a partially sunken steel container, ice, or just plain rocks. The hull may crack, but the aramid will ensure the damaged area remains more or less in place. So if wanting a stronger hull with no extra weight, then first add a layer or two of woven aramid cloth to the front flanks and keel areas of the hull before laying up the chopped or woven fibreglass.

For home builds, carbon fibre cloth for hulls is usually a waste of money unless making an ultra light design for specialist purposes or rich customers.
Aramid is comparatively cheap, about a quarter that of carbon fibre (carbon carbon). It is still more expensive than GRP, but I use much less material for excellent and cost effective strength when used correctly and with a little flair.

Hand in hand with aramid, has blossomed the rise of the structural foams.
These foams are nothing less than superb and available in a wide range of forms.
Most of us know the horrible foam the builders squirt around the neighbours white plastic door frame, where they no longer bother to need do a good carpentry job, and this foam is also mentioned later. But the better structural foams are far better than this and available in sheet and scrim of varying rigidities and densities.
Structural foams are very useful in many places on boats. The various densities can be used as main structural elements with GRP, carbon or aramid either side, or for crush zones and as buoyancy. If a side section of hull can afford to be damaged, then it can be built outside of the main hull, such as an experimental racing yacht, with a light skin of GRP. This offers the buoyancy and shape plus a crush zone for crashes.
If making a wave piercing hull, then you may wish to design a structural foam cored composite impact zone before the first watertight bulkhead, so that any damage will not compromise basic safety and hull integrity. Adding a quickly replaceable or emergency bow / nose may also be worthwhile.

The most common structural foam is the blue foam used to insulate lofts and such like and is an example of a totally rigid, medium density structural foam. The word 'structural' is well deserved as I have built many aerofoils and wings from this. The Rutan Voyager which flew non stop around the world also used it in the wings, as seen from the frayed starboard wing tip on take off.
To this is a wide range of foam sheets (such as Herex) and the pink foams are slightly bendable, but essentially crush proof. The pinks come in long sheets and in various thicknesses and ideal for laying up onto hull moulds or plugs. Many ocean yachts use one inch thick foam sheets, covered either side in woven aramid. Not only is this strong, immensely so, it is also phenomenally light, and in personal experience, easier to apply.

An ocean racer has half its overall mass in the keel because such hulls are featherlight.
The picture opposite shows an external mould using pink structural foam over aramid cloth.

If using foam structurally then keep to the better foams, although blue foam from domestic suppliers is excellent for making formers over which to mould strengthening frames and bulkhead and flanges etc.
(Never use white foam, unless making specialist fuel tanks, where the foam is merely a mould and is dissolved away afterwards. See other monographs.)

For a good cost effective racing hull, use aramid on the outer face, with structural foam and carefully included stay and should lines moulded into this with suitable bulkheads and flanges, then build up with structural foam and an internal face using woven glass mat.
Although not necessary, even a basic commercial hull mould can be built using foam core, by laying up the gel coat, a screen of fine mesh then aramid layer, followed by foam cores, carefully tailored, then an inner core of GRP.
To ensure a perfect adhesion between layers and core, use a massive plastic sheet placed inside and filled with water to press the resin tightly and securely against the foam sandwich construction for a strong hull.
Such sandwiches are rare as most hull moulds are not racing designs, so never truly need the minimal weight construction.

It is imperative to ensure the foam is well tailored to he hull shape. Therefore the first layer may well be made and allowed to cure, then the foam can be tailored at leisure. To ensure the foam bonds to the inner and outer layers securely, it is imperative to use vacuum or some other pressure system to firmly bond the foam sandwich fully and evenly across the whole of the inner and outer layers. On small yacht moulds, I use a big plastic sheet and plenty of water or sand for strong, even adhesion. For maximum removal of excess resin for ultra light weight, I use the more complex and subtle vacuum bagging methods.

Vacuum forming is not overly difficult, just messy and fiddly. Use strong plastic sheets, well positioned, plenty of dead areas for resin to accumulate and plenty of string around the edges to allow the vacuum to form cleanly and evenly. Then plenty of sticky plastic sealing form a domestic window hand injector. Then an old fridge pump which still works. Should cost well under thirty quid to vacuum a reasonable hull or mast, or whatever you wish. See carbon chassis design monograph for more info. Clear plastic sheets ensure minimal wrinkles.
If vacuum forming over a plug mould it is important to ensure the plug does not distort, so always make it suitably strong. The plastic sheet must be off a roll, to ensure no creases.
If not vacuum forming, then use plastic sheets and squeeze and roll excess resin from the composite using standard foam or fluffy paint rollers before the resin sets.

For the ultimate light weight hull, then pure carbon and honeycomb paper as used in the F1 and aircraft industries and the stunningly beautiful Goss Phillips catamaran. For us mere mortals, then judicious use of aramid and GRP cloth and structural foam can make our dream machines at affordable prices.
Most people prefer structural foams because they are a robust and well known technology. If a male mould, then over the foam and aramid sandwich should be a protective layer, even if it's only a clear gel coat to ensure a smooth surface.
Repair of such structures is very difficult and always leads to a weaker structure unless done very sensitively.

If making a mould, then check out the pricing on aramid and foam sandwiches while costing normal GRP structures. You may be surprised by the lesser need s of materials and the lighter weight, with similar strengths.
Never be afraid to mix and match materials but try to keep to one resin type for optimum bonding strength.

The three main resins are the cheapest Polyester resin, then the Vinyl which is preferred for marine use as it more water resistant, especially for outer hull fabrication. Finally the expensive epoxy resins, as used with carbon fibre and ideal for masts and critical compressive structures.

(A rare method of making hulls is to start with structural foam blocks in the back garden, as this allows both a cheap, one-off mould and to use it to advantage. First make a full scale model upside down in structural foam blocks, padded out with a load of blocks and palettes until the outer shape is crafted in structural foam. Then add depth pegs through the structural foam profile to touch the outer skin. I use pieces of dowel. Where the lack of structural foam is missing due to poor packaging, then this is cut and the correct foam added and shaped as required. The profile is coated, often aramid or aramid and glass. When set, the hull is turned upright or on its side, and gradually cored out. Usually by removing much of the inner packing which is not structural foam. Then the inner core slowly carved or power sanded away to leave just a set internal structural foam layer. This can be modified to give variable core thickness were deemed appropriate, tapering off to nothing where needed. Then the internal stiffing added and the internal layer applied.)

If making an internal or external shell on a foam core design, but needing a very rigid core, then by using block structural foam on scrim sheet, and allowing the gaps to open by applying on the curving hull appropriately then these small gaps can be used to build up a resin honeycomb structure which is far stronger than just a standard foam core layup.

Steel.

Self jigging flat packs may seem appropriate in cupboard design and home fixings, but a million miles away from most home build hulls. But with a few sheets of cardboard, some scissors and a keen mind for subtle curves, it is possible to make plenty of cheap models at home until the optimal design is created. To ballast and test the models, simply use tape to hold them together and a quick spray of hair lacquer and some plasticine or modelling clay for adjustable ballast. Then conduct initial buoyancy tests in the bath or garden pool then off to the local boating pond for any keel, mast and sail tests.
Because steel is heavier than plywood, it usually uses thinner sheets for self jigging of lightweight hulls, so will need internal strengthening ribs and bulkheads to ensure minimal distortion.
Welding always involves distortion so the welding must be done carefully and evenly across the hull in a subtle sequence to minimise wrinkles and imperfections.
Upon designing an ideal hull, then it's just a matter of scaling up and either buying steel sheet and marking out, then using a long suffering jig saw along your chalk lines for a small hull. Or for a larger hull, find an engineering firm with an oxy acetylene or a plasma cutter to have your own flat pack delivered to your back garden. After assembly and jigging, hiring a good professional welder will give you your desired hull at a fairly low cost.

As mentioned with plywood systems, the real problem is creating the large curved shapes which will fit neatly together for the ideal hull. This is done with cardboard at first, making a half hull and laying it beside a mirror to assess initial form. Then scaling up in steel sheet, or if making a large steel hull, then making a scale plywood test rig to get geometrical accuracy perfect and as a test hull for initial testing and sea trials.
The picture shows the self aligning bulkhead lugs sticking through the side plates, with wedges used to pull the lugs up tight against the side plates to ensure a perfect fit prior to final assembly. Assembly is done by welding, the lugs ground off, then the gaps welded.

When designing, the internal bracing and bulkhead joins must be carefully studied to prevent fracturing, but this is too involved to include here, so if building a large steel hull, always study a few books on welding large structures and sheet steel fabrication methods to prevent any of the oft common structural booby traps.

It may well be worthwhile to add external abrasion runners along the side of the hull to take any knocks, rather than scratch or perforate the paint and compromise the longevity of the hull. Do not weld these fully as they can distort the hull, but fit lugs to take wooden or hard plastic strakes which do not cause distortion.
Fitting out the inside of a steel hull will require plenty of welding, so always do this and fit extra lugs where they may be needed before sand blasting, so the protective layers will not be compromised by later changes.

Steel will always rust and corrode. Even the best anti rust paints can never deliver perfect protection.
The most common is zinc rich paint. Galvanising a hull with zinc paint is impossible as there are no baths large enough. (BS3236) Cleaning the surfaces and burnishing with zinc is not the same, although a possible option prior to painting, but it is better to be able to sand blast the bare steel on a hot dry day and then paint the hull with zinc paint immediately after for best results, before any moisture can act. Then further layers are painted on until you feel secure. (See also BS2629).

The best primary layer onto bare steel after shot blasting (BS4232) is to flame spray a layer of aluminium onto the bare steel (BS1475) before painting in the usual manner. Aluminium is far better than flame sprayed zinc.
Good reports have shown that 3 mils of flame sprayed aluminium, followed by 0.5 mils of clear vinyl wash primer, then the usual painting has shown superb results after 12 years.

Mild steel is fairly forgiving when welding, but others are not so good. It is possible to build the hull and to weld it in stainless steel, but the cost is high and the welding must be superb and carefully done to prevent distortion.
Extra brackets around main welds will help prevent any long term failure, as it happens to tankers, so it can happen to you. Fractures are probably unlikely as smaller boats and yachts are usually made from a single sheets of steel from bow to stern.

Do not make a steel hull if intending to beach regularly, as steel protective layers do not take well to scratching and can corrode the hull easily. If wanting to do this, then the hull must have an extra layer of protection from such abrasive use. Steel strakes covered with hardwood epoxied in place and covered with stainless steel edging using countersunk screws make a more reliable beaching protection, as does plenty of GRP.
For small dinghies, then simply fit a pair of plastic slip way wheels and a replaceable keel strip.

All steel hulls must use a sacrificial zinc anode.
It is always the anode which corrodes. The zinc anodes are electropositive to both brass and steel, so will protect the steel hull and the propeller and other similar metals. It takes the positive oxygen ions towards the zinc annode and the zinc oxides dissipate.
When a ferrous metal is in sea water it becomes a weak battery and electrons will try to erode the metals. So a zinc anode will dissipate the electrons by dissolving the zinc rather than the steel. The zinc anode must be in electrical contact with the hull. To prevent corrosion when replacing, a thick steel plate is welded where it will do no harm to water flow so that the eroded anode can be easily replaced using stainless bolts and not damage the fully painted surface of the main hull. Anodes are often placed central on the hull, below the waterline of course, and on each side of a larger hull, with some large ships having many anodes. Never paint the anodes.
If you are making a racing yacht hull, then a recessed steel socket should be considered and made before primary painting of the hull, so that the anodes can be replaced and not compromise the paintwork, and be flush with the hull for ensuring top speed. See also BS4360.
See also my marine electrics monograph on the Boats web page on my website.

Because of corrosion by electrolysis, steel hulls also need the likes of stainless steel prop shafts with non metallic bearings to reduce such problems. Likewise for the problems of electrolysis, any bronze or dissimilar metals such as sea valves or other item which need to be bolted, but electrically insulated to the hull, using an insulator such as a Micarta block and secured with stainless steel bolts.

TYPES OF STEELS.

DEAD MILD or low Carbon. 0.07 to 0.15 percent carbon.
Available as Black and bright bars. tubes, wire.
Pipes, chains, rivets, screws, nails, wire. boiler plates.
Easily worked when hot, but difficult to machine owing to tendency to tear.

MILD. 0.15 to 0.25 percent carbon.
Available as Black bar sections and sheet Bright bar strip and tubing Forgings.
Ship plates and forgings, gears, shafts, nuts, bolts, washers, rivets, chains.
Easily machined and welded, and is cheapest steel.
Welds easily. Available in many sizes shapes and wall thicknesses. Preferably non seam welded tubing, but seam welded tubing is perfectly good too.

MEDIUM CARBON. 0.25 to 0.5 percent carbon.
Available as Black bar, sheet, sections and plate. Bright bar. rods, flats and strip Forgings.
Machine parts and forgings. castings. springs, drop hammer dies.
Responds to heat treatment and can be machined satisfactorily.

HIGH CARBON. 0.5 to 0.7 percent carbon.
Available as Black bar and strip Silver steel rod.
Hammers, sledges. stamping and pressing dies. drop-forging dies, screwdrivers hammers, set-screws

HIGH CARBON. 0.7 to 0.8 percent carbon.
Punches, cold chisels, hammers, shear blades, drop-forging dies, lathe centres. spanners, band saws, rivet sets (not rivets). vice jaws.

HIGH CARBON. 0.8 to 1.0 percent carbon.
Punches, rivets, sets, screwing dies, screwing laps, shear blades. drop-forging dies, saws, hammers, cold chisels, springs, axes, rock drills, milling cutlers, lathe centres, reamers. See also my knife monograph.

HIGH CARBON. 1 to 1.5 percent carbon.
Drills, milling cutters, lathe tools, files, wire drawing dies, hacksaw blades, ball bearings, screwing dies and taps.

ALLOYING ELEMENTS.

CHROMIUM Up to 1.5 percent. Used with nickel and / or molybdenum increases hardness and allows high UTS with considerable ductility.

COBALT. 5 to 10 percent. Retention of hardness at elevated temperatures.
COBALT. 12 to 18 percent. Increased corrosion resistance in stainless steel.
COBALT. up to 40 percent. Improves coercive force in magnet steels.

NICKEL. 1.5 to percent. Increases tensile strength and toughness.
NICKEL. Over 20 percent. Used in corrosion - and heat resisting steels.

MOLYBDENUM varies. Used in stainless steels to provide resistance to sulphuric and other acids.

COPPER 0.2 to 1.0 percent. Increases corrosion resistance.

If you have read the above, you will see that the cheapest steel, called mild steel is also the best. This is why it is so cheap, as thousands of tons are used daily. Available in many sizes and shapes.

Steel hulls have high thermal conduction, so they get colder than most boats and suffer from condensation. A good approach to internal thermal barriers is highly recommended on steel boats. See appendix.

Aluminium.
Aluminium is occasionally used for some hulls, usually racing hulls which do not expect a long life, as aluminium alloys tend to deteriorate and fracture, although duraluminium, alloyed with a little copper as used in aircraft, is stronger and will fare much longer. Welding and repair of aluminium is rarely worth the effort, although it can be used to make lightweight upper structures of liners and smaller ginpalaces so that the upper mass is less likely to upset the balance.
Aluminium is normally used on canoe paddle shafts, superstructures and other places where light weight is needed.
Aluminium can be anodised. See my quick DIY anodising recipe on this website.
See also BS5083.

An advantage of metal hulled motor craft, is that the engine cooling system could be integrated into the keel areas, so that the engine coolant can be inboard, against he hull to keep the engine cool. This reduces drag, and has no need for a separate sea water pump. Such a keel cooling system will need a well designed cooling area, such as a large coolant space against the hull, so the heat can be exchanged into the sea water. Some minor distortion may occur from the heated water.

Concrete and steel. (Ferrocement).

The biggest structure to move across the planet is made of concrete and sunk to within a few feet on the harsh oil fields of the north sea.
The earliest French ferro cement boat of 1855 is still afloat.
Concrete has a long and trusted history with the sea since the Romans first used it to make increasingly large harbours, and they even had concrete which could set under water.
Steel reinforced concrete as used in many buildings and tunnels can apply to boats too. Both motor and yachts.

If wanting a strong yacht hull with an integral shallow keel, or a moderate or large motor boat, then concrete should be considered after testing with a model to check the keel mass required. In many cases a ferro cement hull is lighter than a GRP, steel or wooden hull !

Chicken wire wrapped over solid steel bar skeleton, all add up to a fantastic opportunity to make a very cheap and very effective hull.
The present designs are made of small gauge steel bar to make the basic shape, - similar to ribs and stringers, then six to eight layers of fine chicken netting placed over this and all wired together before applying the cement. The ferro cement hull can often be less than an inch thick.
The truss frame method is considered the best.
A basic shape can be made in steel for the keel, main supports and ribs of the main structure, with the intervening areas built up with wire, then steel netting. To this can be welded the ferrous sockets to take later mast sockets, engine mounts and deck supports and such like, but they can be epoxied separately, so the whole steel structure is encased and therefore sealed in cement to remain proof against creeping corrosion.
What can keep a thirty storey building upright can also keep your boat trustworthy. If making an integral long, older style keel then ferroconcrete is ideal. For pod on stick keels then the ferro cement should include extra strengthening and shear zones in the steel skeleton.
If making a ferro cement vessel over a rotten old wooden hull, then always apply a waterproof membrane, as the wood can otherwise absorb moisture from the cement at a critical time of the process, which can lead to less than ideal setting of the cement.

The assembly is to make a frame in the garden, and bend the ribs in steel on a layout area, usually on large sheets of plywood with the hull sections drawn on the wood. This 'scrieve board', allows nails and the trusses made from 5/16 inch round mild steel to be formed to shape and welded prior to placing on the hull frame. These are spaced along a central keel tube, then positioned into place to start the build up of the frame. Onto these trusses are the stringers or ribs, until a wire frame shape of the hull is made, similar to the sections on a hull drawing.
On most hulls, the trusses are made using reinforcement designs of tubular parallel bars, with constant S shapes of wire in between, similar to that found in (straight) roof trusses in smaller factories and supermarkets. These are welded together for strength, as the final steel structure will be increasingly heavy and these trusses will also support the superstructure. See also my welding guide on this website.
Onto this frame is welded many fine curves of 4 gauge steel rod stringers to make up the outer shape of the hull. Then diagonal cross bracing stingers are added inside for torsional strength where needed, and all held together with soft wire ties or welding where appropriate.
NEW galvanised netting is too shiny, so is left in the rain until it oxidises and passivates enough to dull and allow better adhesion for the cement.

Then the netting is wrapped on the main structure, diagonally draped from the gunwales in fully overlapping layers so that the higher density of netting is at the keel area. Again, all held with countless simple wire ties. Further netting layers are then applied, also from the outside until four layers with overlapping joins are applied, depending upon the netting and the size of the hull. Then the strength of the outer can allow four inner layers to be applied and formed to shape to build up the internal bulkhead ribs and other reinforcement areas.
When all is welded and tied, the shape of the hull is teased into a smooth shape using wooden blocks or by tensioning with pliers to remove any bumps or imperfections. At this stage a superb, almost virtual wire and netting hull is made, complete with rudder sockets or tubes, prop shafts and such like all in place, and decking brackets or mounting lugs for other components also moulded into the hull wire and steel structure. If making removable components such as prop shafts bearings, then machined, zinc plated steel tubes can be permanently fitted and welded to the hull skeleton.
During the build, any surface rust is not a problem, but flakes of rust should be removed as they can get larger, so always remove crusts and flakes of rust.
Low lime content cement is used, with hard, sharp sand washed with fresh water through a No8 (1/8 inch ) sieve. On larger hulls, the keel areas should have the cement vibrated to ensure perfect density. If applying the cement single handed, then the outer of the hull is cemented to about half the netting depth, so the later, inner layers will also have a secure bonding to netting, so when dry, the inner surfaces are cemented. Ideally the cement should be a single shot application, with two people one inside and one outside, similar to the ancient 'wattle and daub' process, but this takes much longer to dry. Before drying, the hull is smoothed or faired with a long, thin piece of plywood to ensure very smooth and perfectly curved surface contours. Where there are large unsupported areas of netting, then temporary battens are wired inside to prevent sagging under the weight of the setting cement.
The cement MUST be kept moist as the cement sets, so covering with hessian cloth or old blankets and whatever is suitable, and a garden hose to keep the whole moist will take a week to prevent the cement drying out too fast.
After a week or so, the cement is cured, when the various supports can be removed and the free standing hull is ready for fitting out. Any imperfections can be removed by gentle abrasion. Major imperfections removed by gently crushing the cement with a blunt cold chisel, so the netting remains intact, as the cement crumbles, allowing intimate repairs or modifications, either during the build or many years later when undergoing a refit.
Water tanks and extensions of integral internal bulkheads can now be built as needed, also from ferrocement, but diesel tanks made in ferrocement should always be lined with fuel proofer, as diesel will damage the ferrocement.
Cabin sides and decking can also be built using ferrocement, although made of differing trusses and cement thickness according to the forces they take.
After two months of being fully dry, painting the hull may then begin. The hull is smoothed with carborundum sandpaper then made dust free. A first coating of epoxy paint, thinned 50 percent, then a second coat at full strength. The same is applied inside the hull, plus an extra internal coat of epoxy paint inside the bilge. The upper inner surfaces need not be epoxy coated, and theoretically could be wallpapered ! - But being cement, some epoxy helps reduce long term corrosion in a marine environment, and reduce abrasive wear. Vinyl paint or resin is an alternative to epoxy.

If making a large yacht or motor boat, always consider the ferrocement route, as the engineering skills are minimal. There is no need for a mould and it is far less stickier or smellier than GRP, less prone to rust than steel and lasts longer than high maintenance wood. At any stage up to applying the cement, the process and even the design can be adjusted. modified, and teased into a perfect shape, unlike other builds.
Practice your concrete and trowel skills before committing to the final concrete stage and hire a power cement mixer to ensure good composition.
Repair can be easy, as the underlying steel rarely gets badly damaged, although all steel work should be scrupulously cleaned and prepared before recovering with new filler. Concrete which sets under water can also allow running repairs to be made if still afloat, by sliding a tarpaulin over the outside of a minor hole, mixing and trowelling in place until set to get to a safe harbour.
Fitting parts to the hull is fairly easy and use of extended trusses and netting mesh from the core hull, or to epoxy spreader plates will ensure no undue cracks appear, with main superstructure supports be made in steel trusses as part of the core structure, or brackets added to take wood or steel beams. Final fitting is easier if you have welded lots of steel brackets where needed or have left a few bare internal sections of truss sections with netting, ready to be added to with more steel and netting.

Most home made boats are broad motorboats or day yachts, with good sailing, but gentle speeds, whereas a racing hull has minimal sea resistance and the shape is always optimal for the course, with leaning displacing a different shape to that of straight ahead.
For most people choosing the best compromise, then it's best chosen by talking to owners and watching from the coast on a good (maximum windy) day and watch and compare the various tyres in the harshest conditions. Take notes and use the zoom on your mini cam. You are looking for how they behave in all conditions and their effective speed for the sail area. The hull of a yacht is a can of worms so always research the hull and keel designs. Do not assume all owners are good sailors, so look at the racing competitions wherever possible for the best forms of mastering yacht control and to gauge the levels you desire or may need in your chosen design.

Choose your hull carefully.

If a yacht, then the bare hull is only half the solution, as the hull will tend to be pushed, sheared, bent, and generally distorted in many ways. I have left this part of hull design to superstructures simply because the bulkheads and superstructures can solve most if not all of the forces applying on so many yacht hulls. The mast is often supported by fore and aft stays with side shrouds and these must be resolved into the hull without significant distortion. The heavily loaded shrouds, when under full sail across the wind, must be able to take the very high strain placed upon them and resolve this into the hull, without causing undue stress on the hull. So as can be seen in so many ways, these loads onto the hull cause some high stresses which must be resolved into the surrounding areas.
Stress = load / area. The higher the areas the load is resolved into, the lower the stress. Now add constant flexing and asymmetric loading under sail, then the problems begin to accumulate.
For such reasons, yacht hulls must be stronger than other hulls, as they are a constant resolution of varying stresses and the hull must be able to resolve them with minimal long term degradation. A poor design can cause the hull to deteriorate quickly, whereas a well designed hull can have perhaps five times longer life in a racing environment. Many ex racing hulls are used as cruisers simply because they can no longer reach the high standards under marine inspections.

Just making a stainless steel bracket and fitting it to the hull is not sufficient, the bracket must be able to take the load, but must also have surrounding support so the hull does not distort under load. The hull and how the superstructure is fitted, as may be seen, is the obvious place to resolve so many sailing stresses. Take note especially of the gunwales being pulled up and inwards, and the whole hull bending up at the bow and stern by the mast stays. Likewise the various keel forces. This plethora of forces must be resolved at the design stage, into a whole and balanced machine, and the superstructure is where the lines of compression lie, and to ensure the whole boat remain reliable and comparatively stress free.

Both motor and sail also suffer from constant wave pressure, shear along the hull and the often constant slamming of waves on the lower frontal areas of the hull. All forces acting upon the boat must be carefully taken care of at the design stage to ensure the hull not only remains intact in all conditions, but is sufficiently strong to prevent long term fracturing or other stress related damage of the materials. A modern racing yacht may only have an effective life of a handful of seasons before being shopped out to rest with lighter duties. But for most boats, the long term use of all hulls must remain of major concern unless the boat is to be scrapped before creeping damage gets too far.
Start by making a note of the various forces acting on the hull, the direction and strength of them, and their frequency, and then mark them on the drawings or models. These can now be resolved by deciding where the forces are to be resolved into the various aspects of the design.
On all my designs, I've developed my own systems for assessing dynamic structures and resolving them.
If designing at home, then on intermediate paper and pencil drawings, sketch in the various forces using different coloured highlighter pens so that the resolution of the various hidden stresses can be more beautifully resolved and balanced across the whole structure.
So always design to prevent the forces and their stresses from being too much of a long term problem, and slightly overbuild if wanting many years of reliable use.

Therefore before committing to fit any bulkhead or beam, ALWAYS spend plenty of time getting to know just what is possible from, and needed by the hull. The builder can also flex the hull to see where the most effective bracing can be placed. So get those coloured chalks out and start marking the many and varied forces acting on the hull, how they are converted to stresses, the lines of force and stress, and how to overcome them with subtlety. I mark sea forces in blue, with slamming forces as circles, the mast stresses as yellow or green arrows and comparison and tension hull forces in red.
Some of the commercial 'gin palace' hulls are not overly impressive from a stuctural design viewpoint. It is for such reasons many people do not like commercial designs as boat makers all too often skimp in good design and prefer 'cost effectiveness' in applying core materials. Yuo may well much prefer a small hull maker, and when commissioning a hull, know it has that extra layer of aramid cloth applied where you want it. For example, if making a larger yacht, I prefer the shrouds to be supported by linear aramid tape spreading from the gunwales and spreading out into the whole hull, not just another stainless steel bracket in a fibreglass bulkhead. Not only are my hulls lighter, they are also far less stressed and they remain reliable and sag free, far longer than a standard hull.

I always prefer a little more aramid and little less bullshit when building or specifying hulls.

Like a certain make of wonderful food we have in Devon. What makes it better is how it's prepared and cooked. You do not need the best steak to make a superb pasty, but a good recipe and a good cook. Likewise for hulls.

Superstructures.

Most people want their boat to be a jack of all trades and master of most.
Room to sleep, soak up the sun, be easy to handle in the worst weather and still look good. - For this I can only offer one piece of advice, buy a pack of 200 sheets of A4 paper and a good pencil and rubber (eraser) and plenty of coloured kiddies chalks.
Then take a few months getting it ju-u-u-u-st right.

A good hull can be made or bought - but the superstructure and cabin spaces can be a complete disaster unless you take time and use common sense.

Sketch scale models of the engine, mast and boom, people sitting, asleep, on deck and in the cockpit.
If a yacht, then do so at vertical and also at port and starboard at about 20 degrees.
I like yachts to have the helmsman's sitting comfortably while looking along the upwind gunwale, with good visibility, relaxing, yet in full control and with all dials easily seen. The helmsman out of the way of the crew on the winches. If solo, then all easily to hand with minimal running about.

You may wish to consider that on a yacht, you will be enjoying much of the time at about 22 degrees of lean, so you may wish to design all your upwind seats in the cockpit to work at this angle. The downwind side is close to being awash, so rarely used when under way, unless on a millpond. Carefully angled seating makes cruising a nice experience rather than a chore. This also requires the need for a little padding with tapered cusions when at rest. Decide if you want your yacht to be a sailing design, or a gin palace.
Consider how many times have you had to brace yourself against a cockpit side seat for an hour or two, when you could have been relaxing while under way. This also increases the enjoyment, reduces fatigue and allows you to use the binoculars more easily rather than have to hold on with both hands.
Be sensible. I prefer all ergonomics and controls to be effective. No ego enhancing tat or pose and such crap, but leaving plenty of room for the charts, a holder for binoculars, a cup of tea and perhaps a biscuit.

Sailing is an art, improved with good design.
(Kitchens have been closely analysed and designed for minimal running about, so do the same with your craft. Many ocean yachts have helmsmen at big wheels, standing in the storm, but this really is not necessary, indeed, its asking for many changes of crew on short shifts. Even on more humble craft, you may be fit today, but on a long journey, or having to weather out a storm, you will one day need all the help you have designed into your craft !)

Even a racing machine can be comfortable and safe.

With paper and pencil, and a scale sketch of the craft, sketch in the crew, their standing and sitting positions, then juggle these around under tracing paper and a scale drawing of the hull to get the optimum use of all available space. For initial designs, making a bold line drawing of the hull from three views is easily slipped under a blank sheet and allow dozens of variations to be sketched before deciding on a final design.
Many boats, including commercial designs waste so much space in their limited volume of the hull.
You can do better.

The position of the engine and prop shaft are vitally important.
For yachts, the mast position can perfect or ruin a design.

'Boaties' buy what the designer thinks they need, whereas the builder can actually get it right.

Done well, a boat can not only maximise the use of space, but position the sleeping and living quarters to be ergonomically perfect (especially if tall or short in stature or disabled). The builder will also refine the balance the boat for all occasions, while being wonderful to live on and with minimal hassle from the limited space available.

Spending many hours in the bare hull with plenty of pieces of coloured chalk and a damp cloth is time well spent.

If you include your wife and kiddies in this process, then so much the better.

A few packets of kiddies coloured sticks of chalk will allow you to sketch in, full size, - the engine, bulkheads, sleeping bunks and such like until you build up the perfect layout for the hull.
Start by positioning the engine or the mast, based upon similar designs. Then the bulkheads for best strength, especially if a sailing yacht.
Then consider the main living spaces, as these are always a compromise in small hulls. Then the cabin spaces are minimally compromised to position the places which affect the ballast, such as fuel and water tanks.
Once the engine position is optimised, decide if the engine is to have a working space around it or to be hidden under a seat or hidden under the steps down into the front cabin and how to design engine fume venting to remain separate from cabin spaces. If you have done your homework, then a low profile engine may never get in the way, yet still have plenty of room for access, working and cooling.

Check all walkways, seating, cooking, sleeping and such like and just as importantly, how you can easily and safely move across all parts of the deck and cabin spaces.
When at sea, allow for bracing against the waves both inside and outside. -
When brewing up tea in a yacht under sail, where will you be putting each hand, or bracing your butt ?

Ensure that getting in and out of any deck hatches is comparatively easy and always safe. Decide if this needs shouldered or flush fitting hatches, how they should open and whether they should be hinged, velro'ed, tethered, sliding, swivelling, bungeed or have catches and how any seals should be employed.
Ensure all hatches are easily accessible in oilskins and a rolling, flooded deck. The use of square hatches for equipment is common, but the use of oval hatches can make full body access easier. Watertight hatches must be designed to take the pressure regimes that could be expected, such as turning turtle or an engine room fire.
In this and all other respects, hatch design and retention must be proof from external and internal pressures so will need careful design and stout bulkheads and fittings, which must never fail but always be easy to open by hand in emergency.

In the worst conditions - including tuning turtle, everything must remain in its place.

If using sails then positioning the ideal hatches and the crew moving space will allow fast and safe sail deployment and stowage. Where sails are stowed forward, especially spinnaker, then they are often just stuffed into the forward hatch. It may be preferable to make a separate compartment inside the hatch for each sail, so they won't get tangled ! Being small compartments, forward holds or 'anchor spaces' need not interfere too much in the internal forward cabin space. If using two or three front sails, these can be stowed in large tubes or drainpipes or dedicated tubs moulded into the forward hull and deck, with individually coloured deck plugs (with security tethers), so they can be easily stuffed into simple storage but easily deployed without needing to open any hatch in high seas. It is often easier to remove a sail and stow in into a separate container rather than mess about with trying to take out one sail while putting the other back in the forward hatch while bobbing about on the high seas. Being able to stuff one into a dedicated space first, then connect the line to the other sail in a separate area can be far easier and safer than playing around with tangled sails in rough weather when one sail needs to be stowed and the other needs deploying.

Carefully design any important positions such as a minor forward compartment for sails and anchor, which may double as the toilet in a very small yacht. This is essentially a watertight forward bulkhead to act as a sea proof 'slamming area' should navigation by self or others on the sea go amiss, or the harbour wall come at you far too fast. Make life easier and safer before leaving harbour.
If the forward hull should flood because of a damaged hatch, small areas will be less prone to upsetting stability and the helm. The anchor and ropes can then be stowed where they will do no harm. Anchors need not be stowed forward as is common practice, but anchor ropes should be from the bow, so the boat will safely face into a storm when at anchor. If making hinged hatches, always have the hinge such that the hatch will tend to close when awash with the predominant direction of the sea should the lock fail.

The designer will be limited to some extent by the mast and engine, but all the rest should be open to optimisation and usually in three or four very suitable forms of layout. The final choice may well be a combination of these variations on a theme.

Warning: Any engine compartment must be separate from the living space. If this is not possible, then it MUST have a safe, airtight hatch to prevent any dangerous fumes, and be vented outboard though a safe and water resistant vent. In most small craft, the engine is just aft of central and so can be accessed from the rear cockpit area, with merely a bulge in the forward living compartment on small boats. On small day yachts, the manoeuvring engine is only used for an hour or less and in calm waters, so is more easily vented by opening hatches in conditions where venting is comparatively safe. But when needing manoeuvring in a storm with a broken mast, then this is another way to loose your life from carbon monoxide or other dangers. So it is important to always ensure all exhaust and inlet and fuel systems are safely designed and sealed and cannot cause problems- seen and more importantly, unseen problems such as fumes.
Always be safe before you put to sea.

With the bare hull, placing a few planks over the gunwales will allow the designer to walk about and mark out the space needed for the feet, and where to stand when hauling up a mainsail, while also ensuring good internal cabin headroom and the window spacing, which always juggle for deck space.
Some commercial motor 'yachts' have sleek, steeply angled cabin sides, which may look good, even stylish, but use up plenty of deck space, so always consider that more vertical sides may be un stylish, but offer more deck room and that a compromise is often common on boats which actually get used at sea more than at rest.
Safety first: Never make a mobile ginpalace or sunbathing platform, make a safe boat.

When making a cabin or wheelhouse or steering position, always remember that you will be here for hours, especially in rough seas, so try to keep your position where there is minimal roll and maximum visibility. It's impossible to position the seat in the centre of roll as you will not be able to look forward easily, especially during tight manoeuvring, but at least make life easier for yourself in the long run. Then decide where the others will be; either working, fishing or sunbathing and such like, while ensuring the steering position is safe but out of the way if a very small craft.
Although the hull must be symmetrical, there is nothing to say that the superstructure needs to be symmetrical, although if done badly, non symmetrical designs can be an awful eyesore. Nevertheless if a power boat then the superstructure can be asymmetric, (unlike a yacht which needs to sail at an angle of lean on both sides of the wind). Any asymmetry should preferably be minimally so, if only for ease on the eye.

Take good note of other craft, such as small semi inflatables and realise why the steering position is in the middle, as this is where the surf has lesser effect on the coxswain while getting away from shore into more open water.
If a primarily solo design, then being able to reach everything with minimal effort is priceless.
Disabled sailing begins here, at the design stage, as does easier sailing.
Sticking the wheelhouse high on the top of a gin palace may look flash in good weather and impress the bimbos and bimboys, but in high seats it's a nightmare, especially if you cannot get the hull to plane up to speed to get the required stability. Any high structure need only be used for inflation devices to help restore stability to an upturned small craft and perhaps for working lights where height enables a wider spread of light across the deck. Fitting upper foot and hand holds can be very useful if looking for fish or for rescue purposes.

When designing the layout of your superstructure: Be sensible, be safe, be ergonomic, be stable, be in control and genuinely enjoy the craft.

The cheapest and neatest little solution I ever saw was a Reliant Robin body shell stuck on the front of an 18 foot fibreglass day fishing hull: It had a neat front anchor hatch, fully waterproofed windows, a perfectly fitted rear door and windscreen wipers all attached in one neat design. It could also include the dash and steering if needed for a fully integrated design for far less than the cost of the materials.

Deck fittings.

Do not be bound by convention as it merely holds the designer back. - Always take many looks at all fixtures and fittings, then design at least three different ways to reinvent the concept or need. The final choice may well be a mixture of all three.
I dislike the plethora of fixtures and fittings on a yacht and hope one day to remove most or all of them, and have a yacht which is not only much lighter, but also stiffer, stronger, more responsive and much easier to sail and maintain. Until then . .

Other fittings are emergency and ergonomic comfort fittings, all needing careful study. Making your own fittings of cleats handrails and such like is always personal choice, unless a specific racing class.
Some people adore stainless steel glinting in the sunshine. Others who may not have anti slip sailing gloves or shoes, nor enjoy the dubious delights of the polishing cloth may prefer to craft their own hand rails and even mooring fixings in mahogany or Iroko to match their hull. Some people prefer wooden hand rails which have not been varnished to a shiny finish, but have only been proofed with wood oil as this does not ice up so much and always feel nicer to handle and gives that little more secure feeling than shiny stainless steel ever could, especially in a storm.
Detailing the craft is totally personal and always the choice of the designer who always has free reign to play with any and all variations on such themes.
(I have a friend who simply welds a strip of steel to steel plates and screws these in position as his mooring cleats. It works perfectly because he made them to fit his hull for his mooring. In deepest winter he can even hammer them over a little more so the tether cannot come out even in the worst conditions.)
Being able to secure to your moorings easily is highly recommended, especially on day boats.

Crew and passenger safety lines must be included at all strategic points, especially on yachts where exertion may be needed high seas and exhaustion can lead to a man overboard. So always make sure safety lines fixings are ergonomically designed for ease of use under the harshest of conditions.
Jack lines must be easy and safely fitted at the sight of bad weather. If you cannot attach your personal safety line easily with either hand - then think again and redesign.
Be safe before leaving harbour.

All outer railings should be doubled up with extra handles on the cabin so the crew can walk with at least one hand secure at all times, and preferably two hands in most situations.
Hand rail stanchions should ideally be mounted over bulkheads for strength, with the ends of the steel rope securely affixed to the hull, so should any stanchion fail, the whole rail will remain to save the crew. If making your own, it is highly recommended to polish the stainless steel hawser and then apply a coat of clear vinyl or polyurethane paint or preferably sleeve a clear nylon tube as this prevents broken strands ripping into the hands. The builder may also wish to glue some rubber tube in the stanchion holes, to help reduce localised stresses on the hawser and to stop unwanted rattling. If bare, I like to rub clear ski candles into such stainless steel lines where they are most used. although surfers wax will also offer a little more grip in wet conditions and reduce abrasion problems.

(On racing yachts, the crew can have a modicum of comfort int the worst weather, rather than be personally pummelled and buffeted all night. If the crew have to hang off the side of a racing yacht, then why on earth do so many poor sailors have to sit hanging with feet dangling in a Fastnet race. At least allow the rails to fold out with netting, so the crew can at least lean back and partially relax ! They don't need to be trapeze in scale but fairly sensible and safe and moderately comfortable. Such stanchions must be carefully pivoted and be positioned over strengthened parts of the hull preferably over bulkheads. This system is also used for frigates with helicopter decks. So if you have to stuff your crew off the windwards side of a racing yacht for many hours, at least make them as comfortable as possible; they will at least be that bit fitter for their next watch.)

Climbing up on the high point to view a basking shark should be easy scrambling with plenty of hand holds. Likewise, hanging off the side of the boat with a gaff must be done in complete security from well designed and positioned foot and hand holds.

Simple, safe ergonomics.
If the superstructure has not been built yet, then chalk out a copy on the porch or driveway and test it. If a yacht, mark the mast and pretend to haul the sails and everything else. Note your foot positions then draw around them.
When designing the climbing and walking areas on the superstructure, always climb over the bare primary superstructure with dirty shoes and dirty hands or cotton gloves and socks dusted with bright chalk. - Try every possibility and climbing frame variation. - Now mark all these obvious, if dirty foot and hand hold areas with a grease pencil, then wash off the dirt, paint these areas and dust with sand or use anti-slip sheets along with ergonomically positioned grab rails.
NEVER design stylish grab rails, - they must be very easy to grab and always secure for the user. Any fancy additions to safety items may be added only where they do not compromise the primary function.

Positioning the safety equipment for enough persons on board, plus one which is easily thrown astern for a man overboard, must be well thought out and ergonomically designed, - out of the way of ordinary use yet still remain easy to reach in ALL circumstances.
The rear buoyancy aid for man overboard, should be adult sized buoyancy aid, and not the unreliable inflatable type. It should be easily thrown and automatically deploy with a flashing light, plus the usual whistle and six foot flag on twenty feet of rope. These are often available from surplus stores for a few quid, needing just a change of sea battery to a modern high quality alkaline cell and activating switch connected to the rail. Therefore the crew must be able to access this immediately and is also part of the carefully thought out deck ergonomics. More later.

When the rigging and the primary safety positions are initially sketched in on your drawings and on the actual hull or its layout on the floor, then and only then, may the other less important items be considered.
Secondary considerations include hatches, windows, vents and such like.
The designer may well dislike a window being close to where a foot regularly scrapes it while regularly passing forward. The foot position on deck cannot be compromised, whereas the window size shape and position can easily be modified.

Redesign many times and indeed, chalk your variations on your back garden or pavement, then on the basic hull and superstructure until you have the perfect deck layout. Take your time, enjoy this part of the design process as you can make as many changes as you want, until you feel perfectly satisfied with the result. You may end up with a design similar to a commercial boat, or something far better. - You will have thought through all the possibilities and this is priceless when at sea in a storm.

Winches.
Where hand winches are used, then the users feet must be secure at all times and position the upper body to be safe, yet swing with gusto in the worst conditions. If single handed winches, then add a nearby hand-hold to enabling the maximum torque with minimal effort. If open deck, double handed winches, then make sure they have safety line attachment points and good, anti slip decking.
I always like to carefully consider where the tailings of winched lines will end, then build or sculpt guides or fall areas for each line so the winch does not need the tailings to be tidied out of the way every few turns.
If the superstructure permits, then the lines can all line up towards a single winch either side, and the tailings fall under gravity into narrow long tubes or boxes as part of the bulkhead from the winch to cockpit floor level which take up minimal room and ensure there's no tangling. Seconds saved during a race, not only help to win, but also help remain safer at sea. Making a selection of drop tubes for lines from drain pipes is easy. Just make sure they drain well and the lines are dried after every race or cruise.
Position each winch to perfection.
If a larger boat, then an electric windlass to weigh anchor is useful, but consumes plenty of power. Remember that a well positioned windlass is a jack of all trades, as it can hoist a crew member aloft, (or if a solo craft then add a long remote control). It can also help pull off moorings or other situations, but only if the supporting technology is designed and fitted as part of the overall design.
Vertical winches have the motor safely under the deck. Horizontal winches usually have the motor above deck and may need regular maintenance. Always have a dedicated winch battery near the winch if a small boat, as the power wiring is heavy duty and running long power lines through the boat rather than a nearby battery and simple charging wire is unnecessary and prone to heating problems under a heavy load and possibly fire. I prefer a simple LED bargraph charging state indicator for each battery, easily read form the control panel.
As some anchors come up dirty, ensure the chain falls below decks into a heavy duty plastic tub. The tub should be to the rear of the forward compartment, and as close to the keel as possible to maintain best hull balance. For custom or pristine boats, then the tub can be moulded from GRP, lined with nylon to reduce abrasion and be removable for cleaning. A plastic tube helps guide the chain. If you fit a sea water pump such as a car screen washer to squirt water as it comes up over the deck, then the anchor chain space will be far less smelly and require less housekeeping. A decent stiff brush is just as good. A pristine bilge is a safe bilge.

Spray dodgers or canvas cockpit covers should be carefully designed such that they remain out of the way when folded. The metal or composite roof support should fold out or be fitted easily and the cover easily attached. It must take a heavy sea, as this is its purpose, so build strongly and try to keep all the annoying floods out before they happen, by good design. The windows can be either strong folding plastic or inset thin polycarbonate which must do the job very well in the worst circumstances, when visibility must be paramount. Designing and making this item is not a cosmetic exercise, but one of survival.
For small day motor boats or waterway cruisers, then the powered section of convertible cars always bears a little closer scrutiny. They are usually powered by a hydraulic pump an / or 12 volt motors. These systems also make excellent sub systems on motor boats.

Hatches for deck access panels are either simple panels where the sea can pour down to the bilge, or can be watertight where scuppers are nearby.
Watertight panels should be made with strong panels with synthetic rubber beading. Always mark the forward edge of the hatch so it goes back and fits perfectly. Where a hinged hatch is used, then the seals should be moulded as the last part of the build, after the hinge has bedded down.
For safety reasons, always try to fit flush fitting opening handles on panels. Chandlers offer a range of flush fittings security devices and catches. Cutting a flush hand hold, inserting a small waxed pudding basin, then fibreglassing from behind, and inserting a stainless bar is simple and effective and quite safe to walk over designed properly.
All emergency items must be accessible without use of tools. (Tie wrapping a life-safer because its housing is poorly designed, is dangerous and just plain stupid.)
Where a panel does not need much in the way of a hinge, such as a fuse box cover, then bungees can be employed inside, so the hatch is retained in a high sea, but can be lifted and slid to one side. Always use at least two bungess for long term security, or add a security cord.

When making a final design of a fibreglass deck, it must be carefully supported from underneath and this means bulkheads and cross beams. To further optimise the interior design, the builder may wish to make a dummy upper deck first, possibly in cheap wood to take various chalks and felt markers, then place the users inside the internal volume and simply test where their hands will fall in a rolling sea and where their heads will knock. With this information, mark out the most effective interior before the bulkheads and beams are built, subject to any demands for control, shroud supports etc.
Building up the beams in wood, GRP or ferrocement is fairly straight forward, but consider any options of angled or hollow bulkheads and hopefully a better knowledge of where the beams are best sited, especially for deck mounted masts.

For yachts, the upper deck is alive with the art of sailing, where good layout is paramount for good control. Make every effort to follow traditional layouts so that the control of the craft falls naturally to hand. Then the internal strengthening of retainers and winches can be positioned appropriately for reliable ropework and improve safety at sea.

About these lines must be safety for the feet. In the confusion with a new crew putting up their first spinnaker, all effort must be made at the design stage to ensure a sprog crew have the best chance to remain upright in all seas.

When making decks, first make up the bulkheads and other main structures. Laying up the GRP will need support, but thin GRP sheets can be assembled and joined to allow a basic shape to be refined, and then the structural layer applied over this. Never have sharp edges and all bulkhead flanges should be edged with flat or rounded edging strip or covered with securely bonded rubber edging.
Cockpits and sunken areas should also be built up strongly as people jump off harbour walls onto such areas. Where these cannot be accessed once built, they will need hatches which in turn demand supports around the hatch openings for stepping on and off the boat. When the under supports are made, the upper layer and flooring is laid up so as to be removable so that any watertight hatches can be built strongly and also allow the builder to add drains, storage or buoyancy and such like to be done strongly and neatly.
Always build up internal areas carefully. Ensure you can easily maintain prop shafts and other components and the bilge will pump freely and is easily cleaned to prevent disease. If the bilge is problematic for draining, then redesign until it drains well, then applying fibreglass then plywood then fibreglass. Consoder titting drain pipes into a larger bilge and making drain openings where appropriate. Placing the pump at he lowest point, then boxing in the parts or fitting fibreglassed plywood flooring, temporarily covering the flooring with plastic sheet, then injecting builders foam to eliminate dead spaces. The floors can then be removed should there be a breach in the hull needing emergency repair, particularly in the most susceptible slamming areas.
Leave room for two bilge pumps especially if on winter moorings with just a wind vane and solar cell topping up the battery, as one bilge pump may fail.

Boats often have two stages of build: First under a roof or tarpaulin during the hull build. Secondly when they superstructure in place, then it is best left out in the open, preferably in the rain. - Always throw plenty of buckets of water and play the hose pipe over the whole boat to regularly assess the design and how it is built and works, especially the bilge.
It is better to rip out and rebuild a section when being built, than when it's on the open sea and discover it's less effective than you wish.
Perhaps the bilge has a dead spot or could cause sloshing or instability. Perhaps there is a natural slippy or foot trapping area on the forward deck which needs careful redesign. Perhaps getting in and out of the boat is not so easy as you wish when tied up beside a tall harbour wall. Perhaps the kiddies can't reach an important hand hold - solve all problems early.

Windows, vents and such like are fairly easy, but you may well dislike a window being close to where a foot regularly scraping it while regularly passing forward. Always stand or sit inside the cabin as if you were needing a window or skylight for safe observation at sea, cooking or reading navigation charts before reaching for the jig saw to cut out any windows. - Carefully decide where the windows should be positioned for best effect, then compare with the positions outside so they don't get scratched by feet and also have a modicum of style. Then the final choice of position and shape can be decided.
(Some sailors like a forwards looking window to see where they are going while cooking below decks. While others prefer none, believing that someone sold be on watch at all times, and having a window causes one to get overly observant, or that such a window is a dangerous weak spot in heavy seas. If disliking the weakness of a forwards facing window, then fit a small TV camera on the masthead and run a feeder to a 12 volt LCD screen in the forward part of the cabin if sailing solo. they are cheap and use little power.)

There are two types of windows: Those which must remain watertight to prevent sinking, such as those in the hull; and those which are purely cosmetic which need not prevent water entry, such as around the open, upper cabin areas.
All security windows must be shatter proof and thick polycarbonate is highly recommended.
Security windows must also be able to withstand upturning in oceans, as if a keel is lost, then the cabin space can become a closed survival area, and all windows must remain intact and in such cases, the internal pressure inside the hull may well be larger then that outside and simple windows can blow out. So ocean racers with arm and pod keel which can be easily lost, will need extra security in all sealed cabin windows.

All windows cause condensation, so either make them sealed double glazed, or double glazed which can be opened and cleaned. Fitting a small condensation channel under windows is a good idea unless superbly double glazed. Just stick a piece of waxed string underneath, leading down to the bilge or a drain pipe, such as car windscreen washer tubing, then apply a small bead of epoxy or car body filler, and when set, pull out the string and drill any drain hole. I double glaze using a spacer bar between two layers, the outer polycarbonate and a thinner inner vapour barrier, held with clear silicone sealant, with a small vent at the bottom to allow changes in air pressure and to drain any migrating moisture. If fully sealing the windows, then do so on a very dry day and add some moisture absorbing granules. Other alternatives include anti misting coatings on single skin windows.

Portholes and windows are not difficult to make, as GRP and wood structures can be easily cut through and polycarbonate windows easily fitted with stainless steel screws and plenty of clear silicone sealant.
Some boats with thin hulls such as steel or GRP may use the same as car windscreens, using a rubber strip between the hull and the window. This is prone to deterioration with time, although easily replaceable and should be waxed to prevent early ozone deterioration. If you loose your keys regularly, then one panel fitted in this manner with an emergency key fitted within arms reach may allow such a window to be prised out if desperate. Most builders prefer to very carefully hide a key under an easily accessed deck panel.

Do not use ordinary clear plastic or glass for windows as it can degrade quickly and then shatter with sharp shards which can damage a lifejacket when you need it most. Safety glass is better as it has an intermediate layer of plastic. Polycarbonate sheet is best as it is shatter proof and does not degrade and is scratch resistant. Polycarbonate is often used for bullet proof screens, but not too expensive either, and in various tints. My last supply of polycarbonate was a batch of government surplus anti riot shields, - they are very strong !
Always choose clear plastic as you can always add a layer of tinted film later if needed. Plastic can also be polished if scratched.
Always try making flush fitting windows which are resistant to heavy seas and are safer, and look better too. A flush fitting window is not going to scrape your knees or ankles and will make cleaning the boat very easy. It also looks ten times better than any fancy windows and can be styled to any shape you wish.
If you have a brace of fine engines in the rear, or simply for inspection, then the access or floor panel above the motors could be clear or tinted thick polycarbonate.
Do not make clear bottom or keel panels as these are dangerous in all but carefully controlled conditions. If you decide upon such foolishness, always make sure the windowed section has safety bulkheads which reach well above the waterline: Should the window break, the boat must remain afloat.
The best way to look under the water is to fit some remote finger sized cameras, a switch box and a small LCD TV screen total cost under 200 pounds and far safer. This is the method used by modern submarines, as periscopes are now 'old hat'. They are also very useful when setting up racing propellers. (See also my DIY underwater RCV.)

For windows, the fibreglass or wood is cut-out to fit the polycarbonate window panels. The panels are protected with its plastic film and further covered in food cling film, then a taped in place, flush with the outside surface. Then the inside is built up with sufficient glass fibre or wood to make a secure seal. Upon removal of the window, the moulded internal flange can be cut back to make a neat and even lip. The polycarbonate window can be secured using just silicone sealant, as any sea pressure will be making a compressive force and will not force the panel to open unless the hull is breached in a pressurised cabin. A couple of security screws may be fitted from pressing outwards if this is deemed necessary, although in a sinking boat, being able to force or kick out an opening may be considered very useful if a human can get through it fairly quickly. If your edging is less than neat and the edge gap is a little too big, then simply fit chrome T section beading in the groove as you bond the window into position.

Here is a piccie of a typical commercial window with far too much technology, for which the customer pays through the nose. It is so heavily secured that it's getting too heavy for the purpose, more akin to a security bank vault fitting or for a submarine. It does not look overly nice for the expense, and comparing the sea water sealing of this to the access hatch nearby, then there is no need for such fittings. Note also the placement of the shackle and poor foot placement around this forward deck area.

Many motor boats are used in bad weather. Fitting a windscreen wiper is straight forward car scrap yard technology: Just a single hole for the shaft and a support bracket to hold the motor if things get rough. The single rear car door wipers are best for boats, unless you have a large windscreen or want co-ordinated dual screen wiper action, whereupon the standard car link arms are simply extended with a little welding. Then adjust the length of the arm to suit the window and choice of wiper blade length. If the arc is too long or too short, then simply cut and weld the wiper arm on the end of the main pivot shaft, or choose a different donor vehicle. Grease well and always fit the external rubber boots over the pivots.

Non slip Decks.
Walking around the superstructure with dirty feet and hands will ensure that the anti slip protection is where it needs to be. Go though each and every possible move on your superstructure, and cabin areas with chalky cotton socks and gloves or with greasy boots and gloves. (And knee pads too.)
Anti-slip can be done using the expensive anti slip pads of chandlers, although good paint and a sensible sprinkling of clean sand before it sets is always a better option.
If you are prone to tripping and grazing your knees or elbows, then mix the sand with the resin before application so it has a smother surface which does not scrape the skin so easily, but still retains an anti slip effect. Rubber strips or patterns can be secured to the deck if preferred. Throwing a rubber mat over sanded paint is also a good choice in the cockpit of a day boat to prevent your folding camping chair from sliding about.
Done well, sprinkling of sand can become an art form on the upper surfaces of GRP hulls. Choosing colour co-ordinated sand (from around the world) and careful marking out stylised areas, or even lettering, can make an art form for mere pennies.
Anti-slip paint is made by painting resin where needed, then sprinkling sand before it sets. If you are very careful and use templates, then painting, followed by sprinkling over a template, the builder can have neat, colour co-ordinated or multi coloured patterns for a very artistic look, rather than the usually expensive and tacky stick on anti slip strips of gin palaces. Buddhist monks perfect the art of sand pictures and may offer many ideas. Other masking methods include masking tape, masking using wax or copydex. Contrasting colours can denote safe foot placements when in dire need of maximum security and may be useful on sail training designs.
(Copydex (tm) is a commercial latex office glue, but it can also be used for many other purposes. I use it to protect many items such as windows while painting or fitting, then rubbing off the latex after the paint or epoxy has dried, leaving the window in pristine condition. It can also be used for waterproofing delicate items. It dries slowly to a mild rubbery constancy, and is not very strong unless used for the intended purpose of sticking paper together, so can rub off easily from a gel coated deck after use for masking. I also use it for masking larger or intricate surfaces such as windows where paint spraying is to be done. Can also make an emergency waterproof button cover should any electrical cover become damaged or ripped.)

We can all become becalmed.
Where sunbathing is common, then always plan for this and make ergonomic areas where the sunbathers will not get in the way of sailing or fishing. Not everyone wants to watch the coast for hours, or watch a fishing line for hours, so always make sure there is well thought out room for everyone on a long lazy sunny day with little wind.
Where towels or foam mattresses are to be used, always make the areas non slip as mentioned earlier, so that no one slides about, but will feel reasonably secure while dozing.
Sunbathing is often done just forward of the mast, so that the main sail can still be used to catch what little wind there may be. Such sun bathing (or sleepy fishing) positions should be longitudinal and also sideways, as you will want to catch the sun throughout the day and on all headings.
Some crew may like to sit above the stern of a slow yacht, with a couple of fishing lines trailing behind, so make sure any rails and rod sockets are suitably positioned for a few hours of lazing about, but also safe for storm use.
On becalmed days, the fold out seats are often found on deck. Some tend to slide about in a gentle swell, especially on a slippery fishy wet deck, so always ensure the deck has anti-slip, or fit the seats with stout rubber feet and perhaps a small rim around the deck edges, so nothing or no-one slides overboard while dozing. My favourite spot is across the very comfy rear rack where the crab baskets are oft stowed of a small working motor boat which also does a lot of day fishing.
Where kids like to sit in the bow and watch the dolphins, or just watch the jellyfish and seaweed drift by, then always add a secure steel framework so they can sit with their legs dangling, but never be able to fall overboard, - always add plenty of hand rails where kids are involved and have the upper fixed rail about adult hip (kiddies chest height). Decent rail design allows kids and adults when sitting, to lean over the rails comfortably, with legs a dangling. (With kids, always have one person on watch at all times, and when about to anchor off a nice (warm) shore, practice the man overboard routine at least once a year.)
If wanting a perfect design, consider making the railings and other fittings in mild steel for the first year. These can be easily modified and welded or bent to new shapes for an eventual perfect fit, allowing the boat to be far more comfortable and much safer. Being able to reshape a mild steel rear rail so that you can lean back and fish from the stern in real comfort is highly recommended, compared to simply buying or having a stainless steel item made, but unable to modify it on the boat. After a year, the mild steel railings and fittings can be taken to the fabricator then made in stainless if so desired, or simply nickel plated. If chrome plating, - note that chrome is porous and will rust underneath, so always have a good copper plate layer before chroming.

It is common on many boats to fit stainless steel tubes into gunwales for fishing rods and access ladders etc. So consider adding these neatly if making a smooth fitting upper hull profile. The sockets can be made from angled steel tubes to take the rods. Always include a drain hole. Many of my friends boats have up to a dozen such tubes. If there is plenty of space then consider fitting some deck sockets to take modified old office chairs - the ones which have a central stalk and can lean back are just wonderful to relax in. You may even wish to sit here and use a laptop to do your office work using a satellite or land link, but always make sure you can slide the laptop into a convenient side pocket when something important comes up in the office, needing you immediate attentions, such as a Cod or Conger. Always use removable, waterproof seating or removable padding which can be stowed when things get rough.

Decks are usually white, because they can otherwise get too hot for bare feet in summer. Dark decks absorb the heat. In colder climes, a dark deck can absorb passive solar heat and theoretically help maintain a warn cabin and reduce chance of ice on deck.

Swimming.
On day boats where swimming is common, then adding a rear ladder or even a small platform or a small fold down anti slip platform to take a pair of feet just above the waterline and another step a couple of feet below the waterline with easy access steps is very useful. This will make a swim or dip in the sea fun, rather than a challenge. It also makes using the dinghy far easier. Even just a simple steel ladder bar with pegs which can be mounted in a socket off the rear and stowed with the anchor is highly recommended. Just make sure it fits securely and restrained with a line so it does not fall overboard.
Always fit such steps at the stern, especially on small boats, so it reduces boat movement when getting on board, especially if others are asleep or sunbathing.
Where an access ladder is fitted, it should be near a bulkhead for strength and to resolve any sideways pressure against the hull with rubber pads. Socket holes can vent to sea with small drains if making a smooth hull similar to some power boats. Specialist items can be hinged or fitted permanently.
On day boats, it is perfectly acceptable to simply cut hand and foot holes into the hull, then add the rubber anti slip pads or stainless steel tubular rungs, then build up fibreglass cups behind to make it all strong, seaworthy and flush fitting. For hand hold recesses, I prefer using classic old oval pudding basins which make excellent hand recess moulds and stainless steel tubing.

Sleeping.
If making sleeping compartments, then always have them longitudinal and next to the centre of roll of the boat, as this gives the smoothest sleeping position.
Many people place the bunks at the bow and or near the sides, which is acceptable for 'boaties' when in harbour. But for maximum comfort, particularly in high seas, then choose your bunk well, especially if you have to get up late at night for your watch, when you need all the beauty sleep you can get in a storm. In ocean racers, have at least have one ideally positioned sleeping bunk in the middle of the hull, so that the next person on watch will always be up to the job.

It is worthwhile on a compact hobby boat to try to add a couple of emergency or spare bunks, even if they are only temporary fold down items or merely consist of rectangular holes big enough for a person, toward the aft of the living space, perhaps positioned partially under the cockpit seats. This is a good place for normal storage and wet weather gear and spare sails, but can become emergency bunks for a week end. As they tend to be claustrophobic, you may wish to add small token portholes, so you can also find that emergency sail when all else fails.
Design all spaces well.

Entry into living quarters must always be storm proof and any water on deck must never be allowed entry. Therefore all hatches and entrances must be totally seaworthy. This will require particularly careful study of how the vessel can be swamped, then ensuring all precautions are taken to prevent swampimg. A bad case may be loosing power or sail, in a following sea in a storm swell and the hull slapping up and down on the waves.
There are many designs of main access hatch, from almost submarine quality for ocean yachts, to crafted wooden sliding top designs with 'split barn doors' where the bottom half is sealed against flooding. If the bottom of the hatch is stepped up from the deck, always make the step recessed underneath to help deflect sloshing water from entry.
All open decks should have a camber for safe and fast drainage of deck water.
Careful design is vitally important as any seas in an open cockpit must be ducted overboard through scuppers, and if the holes need to be large, then use wire mesh to prevent loosing filleting knives or other items. Near the main hatch should be drains to remove any water to port and starboard to the outside of the hull. Such drains should have flush fitting, one-way flaps if close to the waterline. Where the cockpit floor is just above sea level, then it is common to vent sea water to the rear of the craft through one way flaps, hoping that cresting the next wave will allow full and immediate removal of any standing water.
In reality, such designs should not be able to ship water and never allow it to lie for more than a few seconds.
The steering position should be fully enclosed, fully shielded from the effects of the sea, or an open cockpit far enough above water level to ensure fast draining.
Be safe before you leave harbour.

There is nothing worse than wet clothing which never seems to get dry.
Even in a small boat, create an intermediate wet clothing area, and a dryer inner sanctum. This may then be very welcome if sailing for weeks and in all weathers. Being able to grab your wet weather gear on the way up on deck or out of a sinking boat also makes good sense. See appendix 6 - heating.

Fitting out also includes cooking.
Elizabethan ships and such like always had the cooking fire in the bowels of the ship, in a position near centre of roll so that it would not upset the cooking pot. It was also heavily protected from catching fire to anything else. Any stray sparks or hot oil would soon fall onto the cold, wet rocks of the ballast.
The designer may wish to consider the wisdom of our forefathers.
Today, in place of a cooking pit in the bowels near the centre of roll, a gimballed or hinging cooker is common and highly recommended if you enjoy cooking, especially on a sailing yacht. Many boats have the galley to one side and thereby only fair weather cooking vessels. At sea, you must always keep your energy levels high and well fed, for you may be in the liferaft within minutes. So always keep the crew healthy, and that means decent, nourishing food at regular intervals. Even if you can only boil water for instant dried foods and drinks, then at least it's hot and improves the spirit.
We can't all have access to bronze casting for a gimballed table of HRH during his midshipman's days. For the rest of us, the hinges of a basic cooker line-up fore to aft. Such designs tend to sway too much, so always have a damped version, even just a small tube and plunger using a modified kiddies push bike pump between the bottom of the cooker to the bulkhead can help damp the design. See appendix.

It is possible to use hot water boilers if you can generate enough electricity, but butane or the preferred butane or propane mix is the normal means of cooking.
If you are prepared to have open flames in the vessel, then petrol cookers have developed a long way since the early flame prone designs, so should be looked at again, but only used in safe seas. For example, the dual ring Coleman camping unleaded petrol cooker is a favourite of many and easily adapted to a swivel design. It is all steel, lightweight and easily adapted, lights easily and reliably.
Just a few minutes to boil water using a petrol stove with a fire extinguisher nearby is far better than waiting forever for a butane cooker to warm the same amount of water. A dry powder fire extinguisher is recommended here.
Cooking does not have to happen inside. - A single ring petrol cooker can give a roaring flame up on deck - even in a mild storm if mounted and shielded appropriately ! So a solo yachtsman can enjoy good cooking if suitably gimballed, damped and sheilded. Even a single ring petrol cooker with a concentric pot and lid will give excellent and fast results. It works for me.
Always prepare before leaving harbour and that incudes cooking in the worst weather. (Rough weather designs available.)
With slow cookers such as making cakes on board and roasting, then other options should be considered. See appendix.

Always check that any cooker you decide upon will be fitted and used safely at all times. Always include a fire extinguisher beside any galley or cooking area. Likewise always check for butane or other heavier than air fuel in the bilge nor floor spaces and always be prepared to vent fully and 'bale out' gasses or fumes where needed. I like to fit a small computer fan and some simple ducting to vent the bilge for a couple of minutes before allowing any flames in the cabin area if using butane or other flammable gases or liquids.
A gas monitor and low oxygen monitor is highly recommended.

Always turn off gas tanks when leaving the boat.
Where compressed gas tanks are used on larger boats, then these should be in separate compartments, and preferably with fireproof bullheads and a lightly made, explosion venting cover to the outside. I prefer to design in the same technology as used in modern army tanks, where the ammunition is held in a compartment at the rear of the turret, but is accessed through a fire wall, where the explosive shells are in a lightly protected compartment with a lightweight roof which will vent easily in case of explosion, without harming the more heavily shielded occupants. Likewise it is fairly easy to build in a low pressure, but otherwise easily sealed compartment for gas cylinders on a boat.
Be it from a small canister of camping butane to a massive cylinder of gas, any fire on board is always a terrible situation to be in, so constantly prevent it from the outset by good design.
Even a simple piece of plastic piping under the galley and a 12 volt computer fan to vent the area will help prevent gas and fire problems, by simply switching it on for a few minutes before using any flames. If you have poor electric power, then use a simple venturi tube above deck, so the wind can constantly purge the bilges of gasses.
Be safe before leaving harbour.

On a yacht in a storm, then the wind generator is a perfect time to use it to warm up food, so prepare that hurricane cooking system now, not later. There is no excuse for not having 12 volt car, cup sized water boilers to give every crew member a hot drink or instant food in a storm. Recently a large racing yacht had to turn back because its alternator failed and so all its electrics failed. On the high ocean, where were the basic back up systems ?
Never forget: Alternators and many other mission critical components are cheap and easily replaced, so there is absolutely no excuse. My alternator cost a tenner and comes from a Ford fiesta - not rocket science, but perfect for the job and spares are often free. My navigation / internet laptop is a cheap ex corporate IBM item plus a backup, both for under 200 pounds. All spares are tested, dried, then stored in very thick plastic sealed, waterproof bags, wrapped in waterproofed protective sail cloth, and stored in the hull, ready for replacement. Yes, the tools and spare nuts and bolts and wire connectors are also ready for use. - NO excuses ! - be it a home made design or the most expensive racing yacht.

On a motor boat or a yacht using a small engine in a storm to maintain some manoeuvring ability does not have to suffer cold food, and likewise in a motor boat, then stainless steel pipes running in, along or wrapped around the exhaust will boil water easily and exhaust gasses can even be employed for cooking. See appendix 6.

Making sure all provisions are secure is a nightmare. So all jars, pans and such like need to be carefully stowed. Some people like to make foam padded containers and storage compartments, while other crews prefer the minimal number of unbreakable cooking implements and instant foods. Others like to cook fresh fish to a very high standard.
It's possible to have a closed compartment with an inflatable unit inside to secure it all from rattling about, and deflated once the seas have subsided. This can be done with strong door catch and a simple kiddies inflatable toy or similar item and a hand pump. Packed sensibly then inflated, this saves a lot of noise and breakage, especially if not using polycarbonate storage containers, cups, bowls, plates etc.
Always have plenty of blue tacky office putty stuck near or around the table, although 'museum tack' is even better. I prefer the white sticker stuff.
Book racks can have small bungee cords which also helps just about everything else if carefully positioned and tensioned. Up in the control area, the modern retractable car cup holder on a boat is perfectly acceptable, and if carefully taken from a scraped car, can make an excellent designer accessory beside the nav display.

Security:
Britain is getting worse: Make sure all hatches and openings are locked and no entry point is easily compromised such as windows.- (Polycarbonate riot shields are brilliant for this). Hide or remove all expensive electronics and valuables. - Make the yacht look 'poor or unworthy' when on long term mooring use ripped, tatty curtains, - let the posh boats take the hits. Remove a vital part for the engine, so they can't manoeuvre out of your mooring in dead of night, or during the day. If petrol, then remove the electronics box or distributor rotor. If a diesel, then remove the starter cable, or if hand starter, remove the handle or pulley toggle rope. Always fit a siren, warning lights, and other items which must never activate accidentally, like so many stupid car alarms. Boat alarms must only work upon genuine active intrusion. For short term immobilisation, fit a removable heavy duty key in the starter cable. - Just make sure all the other electrical security items and bilge pumps work.
Lock the outboard to the dinghy and lock the dingy to the harbour when in some ports. Bicycle cable locks are fairly good.
Piracy is on the increase. Any heavy handed attack on the boat should result in bright deck and cabin lights and sirens. - for both when moored for winter, or when asleep in pirate seas. Flare guns may need to be registered as fire arms in some countries. Taser wires can also be added to arm systems or perhaps in a similar manner to fencing in cattle country, with an intermittent pulse along certain insulated metal deck fittings. They often want your boat for drugs running, so grab all possible weapons and use that radio. If compromised, let the bastards steal your old credit cards and some money, with the real stuff seriously well hidden, including an emergency backup communication kit and battery.

Sails.

Always take careful look at similar sails, as the skills of getting the warp and weft just perfect is an art, so follow the masters.

The main sail of a yacht can be an aramid design for lightness with incredible strength, although it should be folded more carefully, and cannot be furled so easily in a storm.
With careful design, an aramid sail may be an interesting chance to make an advanced sail at home.

Making a sail is not difficult, as even a well sewn old bed sheet can catch the wind and power a dinghy across the water.

Traditionally canvas is the material of sails but this gets heavy in the rain and helps unbalance the craft, although not noticeably. Modern sails are designed to be light and water proof, so they are easy to furl and store, and not get so heavy. Low maintenance sails are a boon, but all sails should always be washed, inspected and stored dry at the earliest opportunity, especially spinnakers and other occasional use sails which are often stowed in a forward hatch and forgotten about until next summer, only to be found in a poor or useless condition or badly tangled with an anchor rope.

Many fore sails are designed to be furled around the stay, so they can be let out a little in storms and fully furled easily with minimal effort, often from the cockpit. Being able to furl such a sail and clear the deck for a spinnaker is so much easier, especially when catching whatever breeze is available. Likewise, many modern main sails are furled on a rotating boom. See appendix.
Catamarans now use spinnaker tubes and variations on this method will surely extend to almost all other craft.

If making your own sails then the technology is a mainly in decent tailoring and superb sewing, albeit in a heavy manner. Always make sure the sail has no tight spots, as the forces should be even across the whole sail for reliability.

For most purposes, spinnakers and other sails should simply be copied from standard sails, ensuring their size is closely matched to the size of the hull for all expected conditions. Make the sail a little large in flat form, then carefully gather in the joins to make a curved form, pin, then sew with strong seams and perfect tensioning. Temporarily edge the sails with thicker cord or tape and watch how it behaves, then make any adjustments and modifications accordingly before final fittings of the details. If it looks weak in places, thread many fine aramid cords through the delicate areas then tension carefully to the corners or edges. The typical modern main sail should have a free cord running inside the edge of the luff, so the curve of the trailing edge can be trimmed to perfection.

If the forward hold of a small monohull is used for the anchor, jib or spinnaker stowage, then have the inner sides fold out as panels to easily stow and deploy the sails safely and neatly. Use nicely curved compartment edges so the spinnaker can be deployed smoothly and with minimal hassle and zero damage. In smaller craft, particularly small racing cats, the use of a spinnaker tube is now popular, where the spinnaker is stowed in a longitudinal cloth tube for instant deployment and to ensure similarly easy stowage. This can also be done in a similar manner on other hull designs using cloth tubes on deck or rigid tubes or tubs designed into the hull. See also appendix 4.

In a power boat, you may wish to add a small emergency sail to get home with - even a simple rig can be sailed with some degree of effectiveness in an emergency, or at least keep you straight in a following sea while trying to repair the engine or water in the fuel line or a clogged sea inlet etc. On day fishing boats, a small stern sail will allow the hull to line up into wind for an easier time when drifting.

Masts.

Making good masts is not easy, as it involves either paying through the nose for an extruded alloy tube, then fitting it out yourself, or making your own from the best seasoned wood, or in some cases, building your own using advanced composites.

Alloy masts have most of the design detail already integrated into the cross section, so little preparation is needed. Tall extruded alloy masts are not strong enough to be self supporting and need to be carefully maintained in position. Extrusions do not have the tapering cross section available with hand crafted masts, but the low weight is a boon and the ability to simply keep the fittings and replace the long extrusion is straightforward. There are many graphs available to choose the most suitable mast dimensions for any hull and sailing styles.
If the mast is deck mounted and allowed to pivot fore - aft in a tabernacle, then the larger masts can be lowered slowly using the boom as an intermediate arm, held by the side stays while the winch keeps the lowering or raising under safe control. This is particularly good in close navigation with bridges, of for testing many different rigs or if carrying an emergency mast repair kit, where parts of the buckled or collapsed parts of the main mast can be sawn out, repair slugs inserted, then re-rigged to get home with a little less sail.
The ability to unplug the details such as wiring, lower the alloy mast forwards using the boom and stays for stability, and a winch for control. Then remove the fittings, fit out the new extrusion, return vertically and re-rig, need only take one or two days.

The base of the mast is simply constrained and will fall over if not for the (three - simple rig, or) four main control wire stays. The top of the mast contains the little burgee wind vane, or perhaps a more complicated weather station, and also the pulleys for mounting the sails, navigation lights, and communications etc. The top and bottom plugs with machined mounting points are simply held using compression and sealed against corrosion. A few turns of aramid and epoxy can help prevent any tendency to swaging.
If buying just the bare alloy extrusion, preferably get it anodised, or be prepared to anodise it yourself. Applying a fine coating of epoxy resin for long term protection cannot guarantee long term reliability that anodising can offer. Fitting out an extrusion is straight forward, with simple foot and head fittings made from welded steel to take the various shackles and other details, with the inserts lightly bonded in place for sealing purposes only, as the mast will be in compression. Stainless steel is best for the job, although enamelled or epoxied steel is also acceptable if the shackle holes are edged with brass sleeving to prevent corrosion. If the foot and head are epoxied in place, then the mast will not be able to be opened for inspection every few years, or to refit wires and such like. Just some silicone sealant is all that's needed to hold it in place and prevent corrosion. I prefer to apply some firm turns of aramid around the outer foot of alloy masts to prevent swaging, as lightweight extrusions are prone to end setting in racing yachts.
If a specialist alloy foot or head, with integral pulleys then this should be machined from alloy billet, then bead blasted and then anodised before fitting. Such an alloy billet can be hand crafted from solid block if costs are tight. (Adding larger pulleys and needle rollers in the pulleys makes for lighter loads and easier handling on the various ropes. Always include spare needle rollers and ensure the fitted items are fully protected with synthetic rubber seals.)
Many people buy an extruded aluminium alloy mast, which has the slider grooves already designed into the extrusion. Extruded / pultruded carbon fibre masts are also becoming available but are really expensive, so it may be cheaper to make your own for test rigs.
The bases of modern alloy extruded masts are often mounted at deck level, and therefore allow many ropes to run internally for hauling the mainsail, spinnaker and such like.
If a heavily used mast, then the sliders should be sleeved with stainless steel or have the runners made from long, nylon edged connections to minimise wear from sail pressures. The alloy must never be allowed to wear, therefore the sliders are given simple nylon abrasive pads. Where steel sliders are used, then consider cutting out nylon simple sleeves or melting Ski Candles onto the rubbing faces to reduce wear and noise. I heat the metal sliders, then aplly the ski candle on the rubbing surfaces. To make simpler sleeves, the plastic of old oil containers is ideal, being HDPE high density polyethylene as used on hip replacements and are guaranteed for 20 years. Can be cut out with scissors and fitted before fitting the sail.
I detest drilling any part of a mast, although most builders allow drilling up to five to ten percent of each end of the mast. I prefer all side stays to be epoxied on wide, smooth spreaders rather than drill any holes. Where a heavily stressed racing mast must have anti shear planes, then I prefer to use the smallest alignment shear pins in the spreaders. Where screws must be used, I prefer a small bead of heat prepared alloy weld, then tap this for greater strength and perhaps stainless steel helicoil inserts where needed. All stays should ideally spread their load smoothly into the mast, to be strong at the centre but gently feathering the force as it is almost zero near the edges. Mine look more like a smoothly sculpted T on their side rather than a plain stick.
Never allow screws to enter the inside of the mast, as they can chafe the internal cable runs. If any items puncture the inner surface, then make up a long slider with abrasive paper, place into position and rub the offender smoothly. This needs a long wooden pole or rope and a slider. I fit a rechargeable electric screwdriver on a raised arm so it can be carefully measured and positioned, sprung against the offender then switched on so the drum sander can do its job. Stop occasionally, illuminate and use binoculars to inspect until perfect. If any rope lines are run internally, then they should be given loose fitting nylon guide tubes. All internal electrical cables should have foam pads glued to them every couple of feet, so they are spaced from internal clanking or abrasion, but where ropes also run internally, then the wiring will need to run in a separate part of the extrusion or lightly glued into place along the safest side of the mast. Glue one side of the aerial and sensor cables, draw through, then run a sponge on a rope to press the wires securely against the side of the mast. I prefer my wires to be on the NE and NW sides of the mast, to reduce abrasion form ropes under the effects of roll and pitch.
The foot of masts can be solid fixing or semi flexible, or adjustable in fittings fore and aft. Some are designed for DIY so they can tilt forwards for single handed lowering with help from the boom and a suitably rigged winch.
Out of the foot will often come a few electrical wires with very seriously waterproof connections for the mast lights, and weather sensors and aerials. These can all be in a single cable for simplicity of replacement, although due to interference shielding, this is not always possible, so check what cables are available for your needs. The electrical sockets should be mounted to the deck rather than to the mast. See also marine wiring and lightning protection.
Where the radar is mounted part way down the front of the mast, I prefer to run the lead up the mast and in through the head fitting, rather than drill a hole in the mast, nor have the radar lead running down the mast where it can be damaged.
Boom fittings vary enormously, with modern self furling sails requiring a specialist mounting. Like stays, I prefer to spread the load on the mast rather then simply clamp or drill fixtures which weaken the mast.
Boom mountings may be ball sockets or pivoted rotating links with hinges for two planes of moment, but not allowing the traditional boom to rotate. Some boom links are far too heavy and complex for their needs, perhaps being designed to fleece the customer rather than do the job simply and effectively, So decide exactly what you need and buy or design accordingly. See booms later.
Free standing masts are the future for many excellent reasons, but are not discussed here as they need a whole monograph of their own.

Masts can be made in four main cross sections; round, oval, pear or delta.

For wooden masts, simply copy those of similar rigs.
Larger wooden masts are built up to make a wooden box structure from straight grained spruce or Oregon. The mast often has four sheets about a finely tapered central core block or a hollow core. Where the sheets of wood are not long enough, they are carefully crafted with finely tapered, overlapping sections to ensure no stress points in the design.

Holes or slots for wiring and such like are made in the core block and never in the outer layers. For ease of fitting, the internal holes should be smoothly coated with epoxy. The wood is then planned to shape, and being of block construction, allows a superb, finely tapered mast. The ends are often bound in steel rings, although I prefer aramid and epoxy. The mast can then be tested in both planes with weights, by mounting on a horizontal test rig to see where it distorts and to then place the stays and other supports appropriately for maximum reliability.

Wooden masts should be lacquered or coated in clear epoxy, so that any degradation can be seen. Painted masts will not allow adequate inspection.

Metal masts are invariably alloy extrusions, which can then be made to measure for your craft, by making your own fittings.

For racing purposes, then two identical masts can be made, complete with fitted strain gauges, then initially tested, with the lesser one then tested to destruction. The data used can ensure the other mast will never be allowed to get close to failure.
Hollow masts are possible, but if making such items, then ensure the building rig is accurately aligned, and pre fit decent sized, full length angle wooden fillets inside the sides, which are then planed and sanded to a perfect fit before assembling the whole with the upper and lower sections. If two halves shaped by a router, then these should be made from excellent wood. Clamp well, preferably 8 inches or less between clamps, and always make sure the mast is true, or curved as required when looking down its length before final tightening of the clamps before the glue sets.
Where a sunken metal sail runner is to be fitted, then this piece of the mast can be thicker, then routed and sleeved, to allow a smooth blending.
For lighter masts, then the core can be lighter wood or hollow near the top, and the whole lightly wrapped in aramid near stress points to prevent early splitting. Do not use aramid with traditional metal rings up the mast, as aramid is low in abrasion resistance.

For composite masts, it is important to understand the power and forces expected of them, then add a good safety margin. Then they must be rigged very carefully to prevent breakage. For larger composite masts, the designer may wish to add strain gauges into the carbon layers to get feedback and early warning of possible limits after initial static testing of the mast and its loading graphs. See also marine electrics.

The standard rig is two side shrouds, and perhaps spreaders on taller masts, with fore and aft stays. Where no back stay is wanted, (simple rig) then the shrouds can be fixed further back on the hull to become running back stays, and should have an angle of at least five degrees to the mast when seen from the side.
Where the mast is weak or in terrible winter weather then a pair of runners or check stays can be added, but are rare.
If you decide to have your stays further back than most, always pad them with baggywrinkles where they may rub against the sails, - just some pipe lagging or closed cell camping mat foam wrapped and tied in place will prevent undue wear on downwind legs.

In moderate and larger craft, the forces expected in these shroud wires or rods is calculated relative to the Righting Moment of the craft. (Rods are about 20 percent stronger than wire by diameter.) The proportional stresses in these ties (under tension from each end) depend upon the relative angle to the mast. For example the fore stay is under more tension than the rear stay due to its steeper angle. Using a solid stay is ideal if using self furling fore sail.
The shrouds have far higher tensions than either fore or rear stays. Please remember that these tensile forces must be carefully rigged to ensure the mast behaves safely and should always be adjusted under heavy sail to get the optimum balance of force to stress where they are needed most.
Intermediate spreader arms allow the mast to be further prevented from bending, but only if correctly tensioned.
Always check there is even pressure on both sides by tapping the lines for the same note and by looking up the mast, as it will curve under full sail, but usually adjusted at rest, then carefully refined to minimise failure when under full sail. Always junk small wire stays and fit heavier for the simple reason that it's cheap insurance. Try not to use swaged fittings, or at least seal them with epoxy to prevent long term internal corrosion, even though they are all stainless.

When rigging the mast, it only takes a moment to tie a piece of cord across both side stays, slightly tighten them, then measure the difference in distance between stay and mast, to check for identical tensioning.
Watching a mast behave under full sail by lying on your back under the mast is five minutes well spent, otherwise if solo, simply use a video camera and transfer to computer for closer assessment. If a with sound, always attach a remote microphone to call out when the hull is hogging or sagging, so as to note the relative tensions on the fore and aft rigging. Always check the behaviour and stresses on the wires while under sail. Get to know them well as this will repay with a reliable mast and safer stresses on the core hull mountings.
Bad rigging on a delicate hull can lead to significant deformation of the hull itself. The hull can be considered as a beam pulled up from fore and aft stays, and pushed down in the middle by the mast. Therefore the longitudinal stiffness of the hull must be carefully considered, especially on a lightweight racing hull. Likewise the side shroud stresses into the hull must be well designed to take the sideways forces under full sail. This in turn demands good design of the hull and how it is reinforced and the placement of bulkheads for inherent stiffness so the structure does not distort too badly and will not appreciably deform over very long times, or cause undue 'rig sagging'. Never underestimate this part of hull design.

Where a specialist mast rotates, (such as vertical airfoil or a large, pseudo wind surfer style) then a taper roller bearing will be needed, as plastic ball sockets will never survive long enough, unless on a very small yacht. The base bearing must be constrained from below for total security. The base plug is commonly an injection moulded item to take pulleys but if making your own, start with a carbon aramid design or a solid block of alloy and ensure the plug is removable for long term repair or to replace the long alloy extrusion should the mast be suspect, or look like it may buckle, perhaps after breaking a shroud. Bead blast a metal plug after machining to reduce potential fracture zones, then anodise.

The many links up the mast make for a neater sail design, but can influence the leading edge of the sail, so any curvature around the mast should be designed to smooth the airflow and prevent leading edge leakage. This is where single airfoil 'wing sails' are far more efficient. It is possible to make the sail with a dual layer wrapped around the mast for optimum airflow with high speed yachts, but can get far too complicated for normal sailing and complete furling is almost impossible.

To make your own mast, it would normally have a sliding groove on the sail side, unless using ancient rings, a slider bar, or a free style sail or the leading edge is fully sleeved over the mast. But for many, the simple sliding track is most common and secured directly to the mast, where it can be a weak point unless using a suitably extruded or manufactured mast.
See also BS MA 28:1973 /1980.
Always use long sliders to reduce the force and wear in the groove. Adding rubbing strips of nylon also helps reduce wear and noise. See above.

On large masts any integral halyard winches and reefing handles and such like are usually mounted close to the deck, so can be mounted on spreaders bonded to the lightest masts.

The main part of a composite mast can be built up using light wood as the former, or if making a very light mast then using a structural grade foam upon which to lay up the layers of carbon fibre.
Before building a composite mast, all wiring tubes and other features should be carefully considered and added where the mast has the minimal stress, leaving the flanks untouched to reduce chance of breakage.

If a wooden mast, then there is no reason why you cannot lightly groove the surface and epoxy in tensioned layers of carbon fiobre and aramid to strengthen the mast or a layer of carbon cloth to give a nice safety factor.
Including navigation and wind sensor wires is also able to make a neat mast. These can often run neatly beside the sail slot without compromising the structural integrity. Where any wiring is permanently fitted, always terminate the cores in a sealed box, then add the component to these preferably gold plated terminals so the wiring remains permanently corrosion free.

On wooden and composite masts, include the all important copper lightning conductor before the build and ensure it will never corrode, and is easily connected at both ends. The conductive end outside the hull should offer a wide area to dissipate the current into the sea. - If lightning is approaching, then at least clamp one end of your emergency car jumper leads from the steel mast stays to dangle in the water, and disconnect all your non essential electronics.

If making a solid mast from scratch, such as for a small dinghy, it is recommended to start with a seasoned piece of wood and plane it with the grain rather than to make it look good, as the strength lies with the grain, not with dimensional accuracy. This is the method used in Longbows made from continental Yew and have more than shown their strength under the most strenuous of situations including Agincourt. Likewise any one piece wooden mast or boom should be made strong rather than neat. Bend the wood to know the grain as you carve it.

Always fit a securely mounted copper strap to the base of a metal mast to take lighting strikes to the sea earth plate.

If making a composite mast, then use structural foam, sliced to take the wiring etc. then the front, rear and sides of the mast core given deep U grooves to greatly increase the resistance to compression. Then fill the grooves with high density foam and smooth. Lay up the first outer layer as carbon cloth over a former such as a strong structural foam, as this helps prevent the tube from crushing in on itself. Make the layers both linear and also some cross biased to reduce buckling. Structural foam can be cut to shape and sanded with silicon carbide sandpaper. If needing internal tubing, then the foam can be hot wired to cut the desired holes, or simply slotted or routed to take the ducting or wires in the rigid foam core. Remember that the hole is also a compromise, so always make a small carbon or GRP tube to insert neatly into the core, so there is no weak point in the core.
Because the beam is loaded from the side, but forces the boat forwards, it is both the width of the mast and its fore- aft dimensions which are important, and as such, a composite design can be particularly broad at the root, tapering up to the tip of the mast. (If supported at the deck, it can be wider at the deck and also taper towards the keel root.) The fore aft dimensions are also chosen to ensure the forwards force is applied with gradually increasing pressure as it reaches the hull. The overall section can be chosen for matching the aerodynamics and not be too ugly.
For long masts, many sections of structural foam with smoothly tapered joins will be needed. On some long beams such as masts, I prefer to slice the foam in an X section and add carbon cloth to this first to further strengthen the internal structure. The cross sections of my composite masts can be rather involved.
Carefully lay up aramid and carbon mono tape over the initial carbon cloth tube to build up the four structural sides and then an outer shell of woven cloth for the final finish. Carbon is used mainly to prevent compression resistance on the forward and down wind sides. In between this I apply side tapes of mono aramid to take the upwind tensile component.
Try to vacuum if possible, - use a long poly tube, with string to allow the air to exit without collapsing, spare cotton cloth to mop up the pooling resin, some plastic tubing for direct smooth finish against the mast and another to seal the vacuum outer containing the string and cloth zones, silicone sealant and use an old fridge pump. It you can build a wood or cardboard tunnel over the mast as it is curing, and fit a temperature controlled hot air paint stripper at one end, then you almost have a vacuum autoclave, and all for mere pennies.
If you cannot vacuum form, then cover the mast with thick polythene then wrap with lots of wide vinyl tape with care over the mast before the resin sets. This gets really messy. Use reasonable pressure, but not enough to distort the layering. Wrapping around the mast will help express unwanted resin, to leave just a low resin, high carbon mast. Preferably cross wrap to give zero bias to the wrapping. Always apply the tape the wrong way around, - with the adhesive outwards, as you only want the clean surface to do the work. Vinyl tape is flexible and thereby applies a constant tension to the mast before it sets so that it works similar to a vacuum, but without the other hassles.
Excess and pooled resin can later be scraped off back to leave the carbon core, ready for smoothing and a final cosmetic coat of clear or pigmented epoxy.

Sail attachment slots or metal channel can be built into the carbon and former before layering, or added part way through the build up, but should be shaped so it cannot be pulled out under any circumstances.
Try not to violate the integrity of any mast by screwing or welding components to the sides. Having U groove flanges bonded and just lightly screwed into the mast may be preferred if adding it to the core mast.
Despite the slot or slider, there must always be a well built mast, with the slot simply a smooth extension to the main structure underneath. Nothing must be done to compromise the integrity of the mast.
Any side stays must be bonded to the main design and include composite spreader plates made from increasingly wider sheets of carbon cloth.

Some older masts are fixed at the base deep in the hull, with a collar at deck height. The most modern masts take much of the load at deck level using large floating, swivelling or rotating bearings. Modern alloy mast are often pivoted at upper deck level, to allow greater cabin clearance, and supported purely by the wire stays. The alloy masts with deck mounting allow easier removal but they rarely get replaced or removed for maintenance.
The single extruded alloy mast is not well designed to be self supporting and will always need the various stays, because if it was extruded with a section suitably strong for a single neck mounting, then the top would be far too heavy. For this reason, custom made tapering composite carbon fibre masts are the only real design suitable for use without stays.
Where a mast is fully or partially supported on its own, the mast can be considered as a double tapered beam with the deck mount being the point of highest load, with the ends tapered to take the load in an even manner. The rigidity or bendabilty may be geometrically designed to bend according to the load, especially if the main sail is attached with skill.
The mast support must be able to take and absorb shocks, so mounting any upper collar in thick rubber will help reduce localised stress points and reduce shock loads from the hull.

Sail airflow.
The wind does not push against the modern sail, but pressurises the upwind face, producing a basic aerodynamic curve. The air flows across the downwind airfoil face, causing a vacuum which in turn provides most of the power.
It is not a big blanket in the wind, like a spinnaker, but a aerodynamic shape which controls the flow of the air to advantage. (Spinnakers are also a little more subtle than a blanket in the wind.)
Take a look at the piccie and note the following. The sail is a smooth curve running the width of the sail, but the leading edge airflow is fouled by a mast, an aerodynamic mess. At least this sail has a reasonable gap between it and the mast, to allow a modicum of cleaner airflow to pass this leading edge slot.

Compare the curve of the sail with the popular Clark Y aircraft wing airfoil section.
As all subsonic airfoils have a thick leading edge, so the mast should ideally be an integral part of the airflow, not some deforming leading edge slat as found on older STOL aircraft, i.e. Fiesler Storch.
The sail could be a smooth airflow from the front edge of the mast, right through to the trailing edge. The more attachment of the down wind airflow, the greater the power and the smaller the sail can be for the same power. The smaller the sail, the less height needed and the more vertical it can remain, possibly with less keelage and thence the more effective it can be to a horizontal airflow.
Admittedly this and other sails are wonderful in their abilities, but they are still far from perfect. A perfect sail for the same power could be two third this size, possibly smaller. A perfect sail of this size can deliver at least 30 percent more power if designed better.

If an aerodynamic or semi aerodynamic mast, then it may partially rotate and this will need a root bearing usually a nylon socket and captive steel ball on a small craft or a taper roller plus a retaining ring. The mid bearing is usually a needle roller and if stays are used to the top of the mast, then a U spreader plate to keep the stays off the mast and a simple bush whose wear can be taken up with tensioning the stays. Any mid swivel needle roller bearing may be held in a hard rubber bush to reduce shock loads.

(I prefer to study mast and sail design as one, at the leading edge of the down wind side, where aerodynamics takes play and makes for the most efficient airflow and maximum power. If the sail attachment slot is carefully designed to blend with the leading edge of the sail, then on small craft, the sail can become an integral part of the mast. If done really well with a leading edge loop of cloth around the mast, can look more like a wind surfer mast and sail combo, which is particularly aerodynamic. Another alternative is to fit the mainsail to the mast at the front of the mast and allow the mast to pivot so the sail is wrapped around the leading edge to give a more perfect airfoil section with minimal separation of airflow. It makes tacking more difficult, but for racing long sections, it is worth the extra few seconds in any race. My own variation on this theme, which I call the Zipp-r-mast (c) J.P. 2004, could not be furled so easily and the mast attachment will need careful design just above the boom mounting, but has certain advantages including very clean leading edge airflow around the mast, vertical furling, while maintaining a good low speed airfoil section and the need for a single unsupported length of composite mast (no intermediate side stays and a rotating boom mount). Rather than use an aerodynamic sleeve on the sail to improve the leading edge airflow, the whole of the mast is designed to rotate and controlled by the boom mounting, so the aerodynamic cross session of the mast will present a smooth aerodynamic airflow across the downwind side of the mast and sail. A little careful design of the boom mounting is needed, with limited play for port and starboard alignments, but is not particularly difficult if building your own from scratch.
I may revive a few of my Clipp-r-mast shrouds which are simple nylon extrusions to clip over smaller masts to extend downstream over the mainsail to give a much cleaner leading edge airflow. With modern data gathering they will be worth reassessing for racing purposes. Being sprung extrusions, they allow the mainsail to turn the Clipp-r around the mast while still allowing furling and tacking. I would probably use a nylon moulded spine with bonded kite material or nylon, dacron and terylene for a lighter, more flexible system, as there were a few problems with the original designs. Not a perfect solution but I consider the old Clipp-r gave a far more efficient airflow than the normal mast systems. Commercial support requested for this and various other commercial accessories. )

The common foresail or jib is today a very sensible design of self furling system, with the forward mast stay being replaced by a fairly rigid alloy tube or wire forestay or headstay with a rigid layer such as an alloy tube sleeve or GRP layer, and is supported top and bottom on pivots. This allows a simple rope pulley to be fitted at the bottom for very easy furling. Because of the force applied on the front stay, regular adjustment of the pivots is recommended. A solid wire fore stay is recommended, with the alloy or carbon fibre furling tube slid over this, restrained with the furling pulley system at the base.

The Team Philips mast is an excellent example of an unsupported mast as an engineering beam, and this tapered design worked incredibly well, with just the base socket being an engineering problem, the rest of the design being superb. Even the dual booms ensured the sails took up perfect aerodynamic sections. A work of art.

Other mast / sails can include vertical airfoils. My first vertical airfoil boat, having good success from the outset. But they look strange and although superb for some high speed attempts, are generally considered not as good as modern composite sails. They cannot be furled in a storm. Nevertheless, the latest tall, narrow ocean rigs are getting very close to the rigid airfoils I made at the age of twelve.
For small boats and wind surfers, vertical airfoils are very easy to fit and need almost no rigging. They work best with catamarans and are ideally tapered towards the tip, but mainly a long thin blade not unlike those of wind turbines now ruining the scenery. (A Plymouth business also made such a airfoil cat but it dragged out development and I was not impressed by any aspect of the design or management. Britain can do so much better than this. I could do much better to a quarter the price and in a tenth the time. )
(See also companion composite monograph for home made wind turbines, vacuum bagging, autoclaves and testing of structures, making graphs during stress testing etc.)
All aluminium masts and booms are invariably anodised against corrosion. (BS1655.)
The custom builder may wish to bead blast the mast prior to anodising, to reduce its chance to develop fractures.

Some people wish to fit steps on masts, such as for rigging up aloft or for maintenance, but with a modern climbers sit harness, then this eliminates such steps and keeps the mast as pristine as possible with minimal structural compromises. Recommended if navigating reefs where a high lookout point is priceless.
Also if solo on a large, often traditional style yacht, consider pulpits either side of the mast if the halyards etc. are hauled manually from here. I prefer caribiner rings on the mast, so you can have both hands free in the worst storms.
Making your own harness is possible but preferably choose a lifejacket which has a big D ding integral to the waist/chest band. If yours does not have a D ring and you sail, then change your lifejacket today. My lifejacket has the big D ring, and I would feel lost without it.

The top of a mast often includes plenty of things to go wrong, such as the anchor light, and perhaps a strobe. Masthead fly (wind arrow), wind speed sensor, VHF and AM/FM and cell phone antennas, and lightning chaser. Radar is more commonly mounted part way up the front of the mast and GPS can be mounted almost anywhere. I prefer to fit anchor lights with two or three lamps, so that I only need to replace the lamps half as often. If you don't like heights, then fit three lamps and three dual core wires, it ain't rocket science. Remember to use the correct marine lamps as they are more shock resistant than the lame items of cars. A bank of many white LED's is another solution, but make sure they point in all directions and add up to a bright and effective light in all directions around the horizon. Twenty or more white LED's will rarely fail all at once, unless the feed wiring is poorly designed, badly voltage regulated or damaged. Many LED's now have 12 volt regulators fitted in them. (If using standard 3 volt white LED's, then these can be actually be powered from just two standard battery cells or a hand torch battery in a real emergency.)
Don't forget the radar reflector. (Strobes are only used for emergencies, but may well be used in heavy shipping channels at night, where oil tanker crew seem to be particularly blind to smaller craft.)
Playing with foreword sails in the dark is not fun, so you may well wish to add a mast spot light shining down onto the forward deck so you don't need to carry a torch when you desperately need both hands, otherwise, invest in a headband torch.

Along with the mast is often the rigging, and especially the stays and shrouds. These can be in various materials, including nitronic rod, gamma rod, cobalt rod, carbon rod, sleeved or pultruded aramid. I sometimes use my own specialist hand made, self tensioning 'soft' aramid items for lighter designs. Positioning of stays is an art in its own right and always worth plenty of study and testing, then careful integration into the hull design such that they do not pull or delaminate any aramid/foam structure. Even in ordinary hulls, good shroud design must not cause unwanted stresses or hull damage. Its a massive and unseen balancing act even before putting the sails to work.
If using swaged ends to shrouds and stays, then always protect them from new with lacquer or silicone to prevent early corrosion inside. They may be stainless, but they still fail. If unprotected, then change them every ten years, it's cheaper than a demasting at sea. Always carry enough rigging wire to make up a backstay from scratch, using decent connections such as the 'sta-lock' rigging terminals. This will allow you to make and replace any stay at any time.
If using a split or Y backstay, always make sure that the join cannot slip too far, should any failure on either of the bottom stays will ensure the mast will remain upright.

When hoisting the mainsail from the cockpit, it always seems harder than beside the mast and is because of the pathetic little pulley blocks at the base of the mast. Using oversized blocks with a decent bearing is money well spent, even if you deconstruct and fit a double rubber sealed ball bearing yourself. While you're at it, to stop all those horrible clankings, the connections at the base of the mast for various pulleys can be reduced and lifetime improved if they are potted in silicone sealant or builders foam so they remain semi ridid at the correct angle at all times, rather than flop about when not in use. This also makes single handed threading much easier. When reefing, use colour co-ordinated lines, or single line reefing for tack and clew, so that it makes life much easier.

Booms.

The boom is not only an adjustment to the angle to the wind, but must resolve much of the side and forward force into the hull. This must be a very secure point of contact to the hull and just as important as the mast. As such, the modern boom is secured by the mainsheet part way long its length, rather than at its end. In some cases, there is also a kicking strap to tension the sail and boom relative to the mast, secured to the lower mast or preferably the deck, to reduce strain on the mast.

As can be seen with modern designs such as wind surfers, the sail need only be constrained at the corner, as this improves the chance for the sail to create an airfoil section, rather than the unspectacular straight line along the bottom. Therefore a boom need only be used to position the corner of the sail at the clew. This frees up the sail to become a more aerodynamic shape and can still be easily furled around the boom if needs be.
The best booms from an aerodynamic viewpoint are those of the wind surfer, where the sail is allowed to take up a smooth shape across its whole, not being constrained by a straight line along its bottom.

At the mid point, the boom is taking as much forward thrust vector as is possible for it in this configuration. If the boom is restrained at the end, then it takes part of its potential force while the mast takes the rest of the force at the mast end pivot. Therefore, to ensure the sail force is greatly reduced from bending the mast, the boom and the mainsheet rope mounting must be carefully designed and is a fundamental component to preventing the mast from breaking. On small craft, the mainsheet can also get in the way if nor carefully positioned. As the mainsheet also takes a high load, it needs to be winched or run through pulleys to ensure the force applied from the sail into the hull is easily controlled.
Where a boom is restrained part way between the mast and the luff, then it is prone to bend, so attaching the sail wholly along the boom or with a partial tether mid point between the sail and boom, then it can be sleeker without comprising strength.

There are graphs available to make a staring point for various alloy section booms, e.g. a 4.5 m alloy boom would be about 100 mm dia. From this can be decided the type of use and positioning of the constraining points.

Two main types of boom; traditional and self furling, roll up.
Standard booms are just a beam to hold the base of the sail, and almost anything will do, as they apply force from both ends and therefore less likely to break, especially if the restraint is at the rear. They can be made from anything suitable or made in composite or an alloy tube for easy furling. Spars need not be too light as the weight outboard of the pivot can also act to load the sail in calmer winds and hold it open in a semi passive manner, although it's the position on the mast and the type of rear restraint which dictates final usage.
Traditional sails were restrained at the end, often with a fiddle block, but modern designs of spars use a mid point restraint so the boom becomes a three point beam, with the forces entering the hull at the mast and mid point in the boom. Therefore the hull will need a stronger traveller mounting, as this force is twice that of a boom restrained at its end point. The mid point traveller is increasingly common purely because control and use of cockpit positioning is easier.
Spars made from extruded alloy with an upper slot makes fitting the sail easier, and also spread the load if the slot supports the whole lower length of the sail such a sewing the bottom cord (plus protective edging) to be a snug fit in the smoothly curved boom groove, rather than through rings or other discrete sliding attachments.

When attaching a boom to a mast, it is better to have a clamp around the mast, rather than compromise the integrity of the mast with screw fixings, especially at this highly stressed lower section. The clamp can be adjustable to allow final adjustment to tailor or suit a new sail and also spread the force evenly into the mast. Using rubber 'twixt mast and clamp will also help reduce localised stress and shock loads into the mast.

The type of boom where the main sail can be rolled or furled for storm duties is very welcome, especially if solo or with an inexperienced crew, where keeping them out of the way is safer than having them 'help' in increasingly bad weather.
The self furling sail naturally needs a bearing or pivot to allow the boom to roll, often a simple ball and socket join, or separate pivots on larger yachts. This in turn needs some form of means to roll the boom and then maintain the partially furled sail with tension. Therefore one end of the boom will need a winch arrangement. On a small boom an end which can be used from the cockpit, such as used for car seat squabs, where an Eaton, trocoid style gearing can be employed for great power from a small power source, or a hand ratchet or crank and maintain the partially furled storm position without slipping. If designed well, then the boom can be rotated from the cockpit end using a small crank or ratcheted lever, not unlike a folding car jack and can be a very useful design for small craft. For very small craft, then boom can be rotated by a simple folding hand lever.
Never allow any boom fixing to fold out or be loose, as it can injure the crew.

Positioning the mast is vitally important for any design of sailing boat.
The sail must be positioned such that under standard sail, with main and fore sail, the centre of pressure acting on the sails, is slightly ahead of the centre of sideways pressure on the hull when at ideal sailing angle. This will allow the pressure on the sails to balance the effect of the curved hull to turn into wind. This is also complicated by the fact that the sail pressure is offset to downwind relative to the hull and also helps to slightly turn the hull into wind. Therefore the mast is offset forwards slightly to the waterline hull, called the Lead, such that with all the forces balanced, the yacht will tend to sail straight ahead, and need minimal rudder, thereby offering maximum speed. This is set up in optimal conditions, at 90 degrees to the wind, and with full standard sail, with a perfect wind such that the craft will sail herself and the keel mass and trimming is adjusted to be perfect. With the craft set up this way, the very best is obtained from the craft, so that when going upwind, downwind or slower, she will also be easier to handle.

The centre of pressure across a modern sail is about one third back from the leading edge and if heavily loaded, may be vary according to the angle of attack and wind speed. The centre of the sail area can be measured from one corner to the mid point of the opposite edge and likewise for another corner and edge. The effective mid point of sail pressure can be found, but not necessarily where the true pressure of a good airfoil applies. Therefore the whole area of the sail must be considered with the tapered line of maximum force/lift, and them mapped to find the optimum point where the sail applies its overall force to the boat. This point must then be positioned relative to the hull such that the hull will track as desired or according to your sailing needs and skills.

To measure a radical or new sail then it can be mounted on a sliding dolly or heavy plate on simple balls, and when under ideal pressure conditions, then dolly can be restrained at varying positions to determine the true centre of pressure acting on the eventual design of hull.

As the front sail is added, then this too must be considered and its pressure zone applied to the hull to improve forward motion.
For speed attempts, being able to tilt the mast forward or backward (mainly wind surfers) to affect the hull steering can also be considered. this eliminates the drag effects of a poor rudder design or slugardly hull, so that the rudder may offer minimal or zero drag to an efficient hull and sail combo.
As the shape of hulls changes with angle of lean, then the effective curvature of the hull relative to the direction will also change, so any heavily leaning hull may be designed to be neutral in effect, or slightly pulling the hull slightly upwind, held by teasing with the rudder, to overcome the forces of side pressure. Therefore careful balancing of the hull shape with regards to wind speed and angle of lean and mast position will make a far better handling yacht.

Winches where needed to work the sails, will depend upon the strength of the crew and should always be more powerful than needed, especially if running from an extended storm with no sleep. E.g. for a 400 sq ft Genoa, use a power ratio of about 30 on the winch.

Keels.

For almost all boats, the keel is a carefully tested stabilising force, meticulously positioned to act perfectly and maintain safe stability in the worst of situations.

As mentioned earlier, yachts keels are available in many forms and should be carefully chosen to match the owners and hull needs.
On sailing barges they are 'barge boards' dropped on each side to reduce sideways movement, while on dinghies they are often just ply wood centreboards or dagger boards.
The simplest is a removable plywood central sheet of a Mirror dinghy where the keel is merely to keep the boat from sway to port or starboard, to maintain stability in the forward plane. A simple plywood box in the keel line will allow a simple sheet of plywood to be inserted without water intrusion.
On racers, the keel is about one fifth to one sixth the length of the mast and with ultralight composite hulls, the keel can be half the overall weight of the boat.
The cruising keel of a day boat may be part of the keel as a deep keel line, where the hull blends smoothly down to the weight at the bottom of the deep hull, as often found on older styles of yachts. The old style with integral rudder is usually too far forward for nimbleness and a separate stern rudder is more effective. This type of keel makes for manoeuvring motor and prop to be easily blended with the keel line.
Some modern day yachts use twin keels of a short, stubby form, which allows the yacht to be high and dry and stable on the beach when the tide recedes and also allows low tide moorings. Many prefer to use an outboard motor as the rear of the hull as fitting an internal design is problematic with poor manoeuvring.

The modern racing keel is a deep vertical arm with a single smooth weight as far under the keel as possible and this has the advantage of minimal drag and minimal mass at its most effective point. The 'weight on a stick design' also has the advantages of being able to be lifted for shallow waters with minimal sail. The mounting of such keels must be immensely strong, but this also allows adaptable forms. By integrating the keel support with the mast support, a strong central structure can be designed, where the hull becomes a flotation device around the sail and keel components. Such keels are an open book for adaptability and minimising drag, while maximising their effect. (Choosing the starting point for a keel, a graph may be needed, and then lots of finer tuning. Always remember that graphs are often given in long tons which are 2240 lbs and similar to one metric tonne. (1 long ton is 'Imperial' 2240 lbs or the lesser 1.12 American 'short' tons.)

Catamarans do not use keels as the upwind hull automatically becomes the counterbalance to the wind force.

The keel is a balancing act. Some keels are simple vertical boards to maintain direction and reduce the effect of the wind gusting, while others are weighted designs for greater stability and to overcome some of the effects having the boat leaning too far and spilling the wind too much in a race.
Many keels are simply short stubby lumps of lead melted on an iron frame and bolted to the base of a hull.
Double keels of day boats and hobby cruising, employ two stubby keels which allow the boat to be beached and remain upright and is an excellent design for casual sailing holidays and for gentle round the world sailing in good weather. It also allows very easy hull maintenance.

Yacht keel security is vital as loosing a keel is tantamount to loosing the boat in some cases. So always make sure any ocean going yacht has two separate securing methods to retain any external keel mass.
To keep drag to a minimum, the bottom mass is usually lead, low in volume and thus low in drag. There is surplus depleted uranium available, totally safe but usually expensive.
The first keel attempt is a test mass and will probably need to be lighter or heavier after initial sea trials, so a temporary keel is usually quite sufficient until the final design of sails and their full working force is decided.

For most people, keel making consists of collecting lead over the years, making a steel main frame with welded upper brackets and a lower lead supporting frame.

To prevent fractures to the main arm, it should be overly strong, as weight here is not too much of a problem to overall design.
Any steel frame should be vibration resistant and shot blasted or bead blasted to prevent potential fracture zones. Again, spraying the steel with aluminium is advisable. Then a big steel container and a large garden bonfire, with a clay mould around the steel frame for casting the keel weight in one go.
Don't just expect a hydrodynamic steel tube to be reliable, as it can fracture from its mounting point, or underwater collision lead to a localised stress point, where every wave is part of the long term failure problem. If possible, always have a belt and braces approach and ensure the keel weight is held by the outer steel tube, fully sprayed with aluminium to prevent rusting with the keel weight cast or strongly bolted in place, but also ensure that the keel weight, like a massive fishing weight has a steel internal runner which is tied inside the hollow steel keel arm to a secure place in side the hull if the steel tube breaks. You still have the keel weight, but the boat may not handle at all well, but it may still stay upright, which is a small price to pay for fundamental reliability. Far too many racing yachts are lost through lack of preparation. If making a composite keel, always have two separate supports, one in carbon with aramid, or in steel, and another internal purely retainer in aramid or stainless steel. Supporting the keel arm in rubber may also be worthwhile to reduce fractures to a delicate hull and offer a little collision resistance. If the keel is allowed to unlock and fold backwards when entering a shallow harbour with minimal sail then this too, is a good idea, especially for underwater collisions.
So if building a high speed cruising day yacht for general purpose, and have decided upon a racing style keel, then simply have it pivoting backwards, and restrained in working position with a spring, so that you can furl and coast up to the beach with minimal sail and lift the keel up safely for the best of both worlds. With mini side flukes on the hull, it may even remain upright on the beach at low tide, but side posts are recommended, preferably with large flat feet.

Onto the steel keel arm of more involved design, can then be built the minimalist drag of a hydrodynamic shape. Any steel arm can be aluminium sprayed then nylon coating to protect the keel arm and reduce corrosion. This nylon can be sprayed or melted on, similar to that used by skiers for repairing the soles of skis. This is all blended into one smooth shape with nylon or epoxy coating.
The keel must be accurately aligned and symmetrical. The upper mounting will depend upon the design, but must always be fail safe. Where it pivots then the pivot must also be corrosion resistant and reliable in use. Nylon bushes on stainless sleeves are possible, but I prefer aluminium bronze with attendant greasing points to prevent sloppy action after many years. Where the keel is retractable or folds back, then this too must be carefully designed. See also aircraft undercarriage for more ideas.
Where the keel simply drops down into the keel slot or pulled up from below if it has a lead mass. I often prefer a keel (solid or adjustable) with bulbous lead mass, which lifts up for easy trailer transporting, and drops down into position, held by a breakable tapered sleeve for rigidity, security and simplicity.

The modern yachts seems to prefer fixed keels which have no safety response to underwater debris such as a container or a waterlogged log, other then a replaceable hull section around the keel root. The modern bow may just kiss the waterline to prevent such problems and possibly help deflect minor debris in the laminar flow, but the keel still remains a design sore spot. In many cases, minor underwater collision may do little damage if at a glancing angle, but there is no reason why a modern racing 'arm and pod' keel cannot be self protecting.
For greater collision resistance, the keel arm can be angled backwards to help deflect floating obstructions. If the mass of the keel weight is in the correct position, then the arm need not be vertical nor terribly prone to breaking. This can also reduce any tendency to flutter.
The traditional fin and older yacht keel may well survive adequately indeed safely, but modern racing designs evidently do not. This design is increasingly common design on smaller hulls (even more so on 'foil Moths) and as such is capable of great improvement in many aspects of the basic design.
The traditional method of hull retention using many inch stainless steel bolts holding a keel to a glass hull can often result in serious damage, whereas a keel capable of shear and remain reasonably attached, will at least offer some safety factor for the crew.
I believe keels have a long way to go. The ability for the keel to distort and in some cases even flex with pitch is considered in some of my designs, such that the keel is no longer a passive component waiting to be damaged or lost.
A keel arm which is lightly sprung such that it just overcomes the majority of pitching motion, (or even free to pitch if the hull has a high polar moment inertia), will be able to move backwards in an underwater collision then drop back to station to thus prevent capsize. To enable this, the use of a simple fail safe hinge is not rocket science and may even be designed to allow it to become lightly corroded and encrusted for better rigidity, without loosing its inherent effectiveness in a collision.
There is also the possibility of a keel which is sprung loaded such that shock pressures on the sail can allow the keel to deflect slightly, to slightly reduce some shock loads on the mast and its shrouds and reduce hull degeneration.

For maximum racing effect, a yacht keel should be light weight for speed and ability to change direction, and this means a deep, thin keel with maximum mass at its base and positioned under the centre of yaw of the working waterline in racing conditions. Unfortunately in shallow harbours, such an ideal keel is unmanageable and is a problem, although a retractable keel can be used by pragmatic designers.

In 1970, I proposed and proved a tilting keel for yachts, but no-one Plymouth was interested. My design used a link to the bottom to the mast, such that wind sideways force would greatly lever the keel into wind, without upsetting the shrouds. This allowed maximum sail power, with the keel close to the upwind surface and the keel arm, being airfoil in section was also pivoted slightly at an angle to the horizon so that it would also add a secondary downward force, in an opposite manner to a hydrofoil. No-one was interested in 1970, although a lesser form is now used in modern racing yachts. If only British engineers and innovators could be encouraged to develop their ideas, rather then watch foreigners take all the profits. (e.g Virgin buying Italian tilting trains and Blair buying French aircraft carriers for the Royal Navy.) My present keels are more advanced and await patents and support.

On power boats and motor boats, the keel is less involved as with yachts, but just as important. The keel mass is usually positioned along the keel line and can often be adjustable to act as a trim mass. See later.

See also my wind tunnel monograph.
See also hydrodynamic testing of scale models, later.
See also sea trials and adjustable ballast, later.

Keel test: Yacht.

When testing, I prefer to tilt the mast away from a nice, nearby sandy, sloping shore, so that should the craft sink, it can be gently, if ignominiously dragged to shore with a rope around the keel, to await low tide for serious modifications.

If not self righting promptly, then a heavier keel is of course needed or perhaps a reassessment of the design. This test must be done with all hatches open to ensure the inherent buoyancy is also adequate. Therefore it is common to do this test before final fitting out, so that any important changes can be made.
If you are fitting out a racing design and want the minimum keel mass, (relative to the depth of keel), then have a dinghy nearby with extra weights which can be clamped or tied on to assess the most effective keel weight. Then after it self rights as desired, the keel can be rebuilt using the new optimised keel mass.
Designers of large yachts use previous knowledge of similar craft and intensive calculations to decide the keel weight, but no two boats are identical, and in my opinion, this test must always be done and is the only true way and the most reliable and proven method of checking keel mass. This test must also be done after a full rebuild or other core changes to the design, such as heavier mast or more sail or a new keel design and such like.
While the boat is fully over, take this opportunity to see how the hull sits sideways in the water, as if it's too low, then there may be a buoyancy problem. Ideally the hull should sit about half way in the sea on its side or less, with all hatches open, with just the foam buoyancy supporting the hull. The weight of the mast, (wet) sail and keel are usually just on the surface, partially supported by water displacement, so the working buoyancy is rarely equal to the mass of the whole boat.

There is a tendency for some ocean yachts to add foils to the side of the keel mass and although I consider them a moderately good idea if active, they can only apply a passive force if they are designed to add an extra downwards force (and drag) to the keel mass. (Delft university 1980-4. Gerittsma and others). So if deciding upon keel flukes, always make sure one is applying maximum down thrust on the upwind side, and the other is almost neutral in effect. In the example shown with upthrust flukes, one tries to pull the keel upright, which would be ideal if the other fluke does nothing, but the other tries to lift the boat out of the water to reduce buoyancy, negating the effect somewhat. In reverse, with downwards flukes, the keel is pulled down into the water, not unlike having a greater mass, but a resultant force that unfortunately acts in line with the keel rather than pulling down in the preferred direction of gravity. Getting symmetrical flukes to act sensibly is prone to problems and only sensible if they tilt in opposite directions according to the hull angle. This means having fixed flukes pointing at a compromise angle is often semi productive with dubious results.

I still prefer versions of my original 1980 design 'Actikeel' (C) John Partridge 1980, where the keel tilts sideways to offset the mass, and / or the lower part of my keel shaft has a rotating vertical plane to apply a secondary vertical alignment force, with minimal extra drag. The motion of these components can be controlled by hand, or by applying power from the boom line or mast side stay loadings for automatic use, or directly from adjustable rudder control for tight racing versions. Just sitting upwind while pushing a spring loaded keel lever with your foot so the keel mass is under your bum is very natural. I can mix and match the two variations, especially on test rigs, but generally use the leaning keel for yachts with rounded hulls, as minimal side force is required. Yaw being controlled purely by hull design. Where the sail area is massive or the hull is more squared which can take the sway easier, then the rotating lower blade is used, or both methods used. The pictures are simplified, but show the basic concepts.
On one man hulls, my budget keel sits central, with a simple foot lever allowing the yachtsman, instead of putting the feet on the opposite gunwale, to push against the foot lever (with straps), to very easily lever the keel under the upwind flank.
For high sail area designs, the keel also tilts on a carefully angled pivot, to add a secondary downwards 'negative hydrofoil' thrust from the shaft blade. This is still under development and part of of one of my thesis. The amount of lean can be easily adjusted to match the wind and sea conditions. The different types cause different eddies and underwater effects, and are chosen according to the type of craft. The milder types of sailing can have the down thrust type, whereas slicker designs usually use the tilting keel type for the cleanest water flow.
Many dislike the way that the sail leans downwind and therefore never really gets a good chance to maximise its aerodynamic potentials. I am now developing a series of test rigs where the keel mass position of a mono hull is automatically adjusted by the pressure on the sail, such that the mast will remain upright as possible to enable the smoothest and maximum effective airflow over my sails and its variations. With modern curved racing hulls, then a large slab of suitabley curved lead which slides/rotates across the inner keel area may well offer some interesting solutions with minimal drag and no keel problems.
(If interested in any of my designs, please email. Dependant upon your needs, I can design, develop and build, or have some built to the requirements. My design and developments costs are much lower than others, as I enjoy this aspect, and cover my costs from manufacturing, support and licenceing. In some cases, the customer and originator of the specification can retain sole rights for up to ten years. I also have varous thesis, mostly finished on the Actikeel and other of my keel designs, plus suitable racing hulls, but have been unable to find a university to allow me to do a post grad study for a masters degree. I already have two degrees, in science and technology.
Please help. )

Keel safety. (Thesis E).
I dislike the way ocean racers loose a keel and just seem to have a death wish and want to fail. With more and more containers and timbers floating just below the surface, racing in Antarctica and such like, then loosing a racing keel needs far better design. That's why racing cats with no need for keels can be safer.
These keel arms suffer atrocious flexing and other stresses, and as such, are naturally prone to breakage simply from standard use. Therefore they must be heavily over specified and include a back up support systems.
The self righting test can also be done to ocean yachts, where the keel has been ripped off or broken or the mast destroyed, to see how the hull behaves so that it can be made into a safety hull by removing the upper mast with explosive bolts to turn a racing hull into a safety shell. It's far better than a few days in a life raft and far safer. At least the hull contains some warmth, radio, food and water. In some cases, an emergency stub keel can be used, and a mini sail to maintain some control in a storm. For such reasons I prefer to include a stainless steel chain hidden inside in my larger racing keels, so that if the weight breaks off, the weight does not sink, but there is still something to keep the hull moderately upright. Ideally, then keel arm should break at a pre-designed position, so that the lower sleeve can be slid up into position to make an effective racing keel. Adding extra weight here is not a problem, and properly designed, a racing keel should be able to break off on a submarine, container or whale, and still be able to remain with the boat until the lower sleeve can be slid into position by a diver, to safely return to harbour or even continue the race. (In an ocean racer, I would include that when the immediate damage to a keel, it should also trigger an explosive bolt in the top of the sail to spill any wind, so the boat remains upright. This requires very carefully made and placed safety sensors, but is far better and less expensive than any liferaft. (Email me for more info.)
An ocean racing keel consisting of a weight on a stick is no longer acceptable.
Be safe before leaving harbour.

(As an aside, I recently saw a good variation this theme, where a yacht with a tall mast needed to loose 10 feet to get under a bridge. The owner had therefore tied some massive water bags to the upper mast, with lines exactly designed such that when the heavily loaded water bags were pushed to one side, and the mast and craft therefore leant over, the bags would sit in the water with no more load, and the measured lean was perfect to clear the bridge, without dismasting, and just needing a water pump and some bags. A simple and effective system for a motorised yacht to get under a bridge.)

Keel test: Motor boat.

With a self righting design, then the restraining rope is released most of the way to note the turning turtle position, and this is carefully noted and photographed or videoed. Hopefully no wash or waves from other vessels to upset the tipping point. Then the boat is turned completely over until it is ALMOST upside down. (You may not want it turning completely over and smash the cabin against the harbour wall, so the strop will turn the cabin towards the harbour wall so that the return back up will be in clear water, hence the need for a crane with a jib. ) The quick release is triggered and the video or stop watch used to assess the response time. Again, use a video. It if fails to right, then the crane and low tide will be useful or a diver to apply another strop to re-right the hull.
Always make sure only the holder is near the safety rope.
A boat that rolls fully over may well have a certain amount of momentum and thereby will self right faster on the way back up the other side, whereas the static test will ensure the boat is stationary at its most unstable inverted position and therefore the response time will be the maximum for this test.
As these tests are rare, it is common to clamp a waterproof video camera in the bridge for fun, and a second video camera overlooking the engine compartment, protected by a sheet of polycarbonate, to enable the designer to see where there may be any unusual long term problems. The videos should be copied to a computer and re-run many times to study the response and centre of gravity and any polar moments which may need modifying. The local press may also be interested, if a reasonable size boat.
If no crane, then this could be done from a bridge or similar means of applying a vertical load on one side of the hull, but must always have facilities to rescue a drowned boat.

For an accurate assessment, then the bow or stern can be fitted with a large white disc, marked with degrees, (or a push bike wheel with the spokes painted white), so they can be used to accurately measure the degrees of rotation. Adding a pendulum to the centre of the disc will act as an indicator.

Rudders.

As can be seen by this rudder, it sticks down into the water a long way, and the reason of course is that it expects to need this depth to maintain control. Therefore it is reasonable to assume this hull will be used in all seas, where the rear of the hull is expected to be many feet above the waves at some times. The deep keel and round hull shows that this hull will also spend most if its time at high lean angles, where a deep rudder is so desperately needed. This is a very sleek yet strong rudder and its mounting is also phenomenally well designed to fit into the aramid hull. (Scale: gunwale to keel weight = 30 feet.) An upgrade to this hull would be to have a wider arse, and two widely spaced, angled rudders which will ensure maximum lean with maximum rudder control.
(When racing yachts get old, and they do very quickly due to deterioration in the hull, then I'd probably have the keel of such a boat retractable, built into a rubber mounted tunnel and winched up for shallow moorings. This would make the yacht easier for when its passed its racing days and thus access any harbour using a small retractable internal 'outboard' motor.)

Modern broad arsed racing yachts will use two rudders, offset at slight angles, so the one in the water will be perfectly aligned at the optimum sailing angles, and the other may well be out of the water. These are usually balanced spade rudder designs.
Fitting a racing yacht rudder is to ensure it does not fracture from constant strain and minimal hydrodynamic ripples is problematic. The rudder may therefore be a long tapered metal beam riding in twin taper roller bearings, or in machined alloy bronze bearings, which can apply safe loads into both forwards and sideways loads into the hull. This is where intelligent use of aramid is highly recommended in a hull. The rudder blade is built around the shaft which would be about half to two thirds the depth into the blade, so that any damage will not totally trash the whole rudder. They should be easy to replace.

For cruising yachts, then rudders have many and various designs, of which the skeg is most popular.
With motor boats, the ruder is often integral or partially integrated into the keel line and part of the keel lone to protect the propeller or propellers.

The rudder positioning is chosen according to ensure the required amount of force for safe control at high speeds and also the amount of rudder movement needed at the slowest, tightest manoeuvring speeds.

Maximum rudder angle should not exceed 35 degrees as any further, the water will burble or eddy and cause excessive drag with lessening effectiveness.
Only outboard motors and bow thrusters can offer greater manoeuvring angles in still air.
On racing yachts, the rudder is usually an airfoil shape such as NACA 0012. And like such profiles, the effective lift or pressure is about a quarter the way back from the leading edge. This is where the rudder shaft is normally placed to resolve the forces and maintain good balance, or the shaft placed just a little way forward of this to reduce any tendency to flutter if a poor bearing design or a lightweight shaft or the blade is not cleaned regularly. In many cases the maximum effect of such a profile is about 15 degrees in water, and from this the way the rudder can control the craft can be assessed. In reality, the ruder may well be part way out of the water and real life testing will always be required to ensure the design works safely and effectively, as there may be unknown hull eddies or such like at certain situations of heel and other conditions like hogging. This is where a racing yacht is tested in a test tank under maximum racing angles of lean to ensure the rudder can genuinely control the craft.

For most water craft, the rudder shaft dimensions and bearing sizes and control linkages are straightforward standard engineering.
In larger motor craft, where there is powered steering, then anti hunting control systems will be needed for when the ruder is partially out of the water and the power supplied can cause unwanted or excessive movement.

There is the constant intent to use simple pins and bushes on many rudders and this is excellent for most smaller craft. For larger yachts, such as ocean racing, then the use of bushes can lead to high friction forces and wear, so adjustable taper rollers may be needed as the hull structure settles down.
Larger craft and motor boats use bronze bushes and a small axial load bush. The use or needle rollers demands good lubrication and sealing. (I'm developing my own bullet proof pivot systems which eliminate not only wear, but also slop and friction, while keeping the rudder deeper in the water at all angles of lean and at a more effective angle, while leaving just a fine and smooth control system for this otherwise ancient design. It also allows very easy rudder repair. More to come as development continues.)

Steering control is the classic rudder arm or the extension arm of small yachts. Then the small rope or rod or cable system of medium day craft, leading up to the hydraulic ram system, either manual with wheel or with motor driven hydraulic pump.
For small boats using modern car engines, then take the opportunity to also use the power steering of the car too ! Keep the power steering pump and use the steering rack to control a large rudder. Rocket science it ain't . In most cases, this is not needed unless using a powerful car engine, or pair of engines. (Naturally, if the car engine also drives air conditioning, then this can be used to power a refrigerator. So always keep your mind open for a sensible life afloat.)

The day cruising yacht with dual keels for easy beaching need a long skeg type rudder, to become the third leg for staying securely upright when the tide goes out. This skeg must be able to take up to a third of the weight of the whole boat and not sink into the mud any easier than the other two keels.

There are other methods of steering such as parallelogram catamaran hulls, where the hulls slide parallel to offset the heel force enough to affect competent control with no resort to rudder drag. This positions the mast relative to the downwind hull such that it can control the tendency to turn into or out of wind. But this development has far to go and will probably never be suitable for inshore racing circuits, where a rudder will still be required for tight manoeuvring.

On wet bikes and ducted props, then the nozzle may be the design successor to the rudder. Where the jet nozzle is not under water, then the deflector is still acting as a rudder, even though it may not touch sea level, but it still obeys Newtons Laws.

The Voith Shnieder propeller is the rudder. A separate keel vane used merely to react against, to enable the craft to turn in its own length and for straight line stability when full ahead. The same applies to double paddle wheelers.

As this is a short guide, paddle wheels and other means are not considered here.

Engines.

For larger craft, I always refer to the Borner and Witte nomograph to get a starting point for the engine size for a hull.
I offer my approximate copy for the interweb thingie. Fairly accurate, but like all such items, only used as a guide.
Start with the waterline, then draw a line across to the displacement in (long) tons to make a point on the right hand base line. From the point on the right hand side base line, a line can be drawn though horsepower to the left hand side baseline, then another line to read the speed relative to a round or a chine hull breadth to width ratio.
This gives a good starting point from which to develop a final choice of design with a reasonable engine match for the desired performance.

The example lines are of a 60 footer, weighing ten tons giving a point of the right base line. It has a 200 HP motor which gives the second point on the left base line. The line to the breadth to depth ratio shows the boat will be capable of about 14 knots.

The nomograph can be used in many ways, starting with whatever parameters you need, - just use the lines in the order, to work backwards or forwards to decide on the right power for a hull or best hull form for speed or whatever is needed. For example if someone has a favourite engine and needs a certain speed, then the nomograph can offer a small range of weights and waterlines which can then be chosen according to the waterways or open water to be used. These can then be double checked using the approved sequence described (using the number sequence at he bottom of the lines.)

All early approximations need to take into account the inefficiency of propellers as mentioned later. See also props and wake factor.

If you have a craft which does not vary too greatly from a similar craft, or a similar hull and engine, then you may be able to a good working guess of the relative differences to choose the size and pitch of the optimum propeller. If needed, it may be preferable to make test runs up and down a set piece of water. By doing runs in both directions and calculating the average, the optimum readings are obtained. This will show if the engine is struggling or being overloaded (over-propped) or over revved (under-propped) at the desired speed, and thus in need of a coarser or larger propeller.
Into this assessment must be taken the way you treat your hull. If you only scrub the hull once a year, then barnacles or seaweed will slow down the hull. A poorly maintained hull can lead to a 30 to 50 percent decrease in speed. Half way through the season may be the best time to optimise your propeller choice, otherwise, get into the dinghy and scrub that hull with a stiff broom one a month or more.

Choosing the horsepower of the engine is therefore dependant upon skill and calculations, although the best and easiest is to use similar power to those of similar craft for the speed and fuel consumption that is desired. The propeller is matched to the hull and engine, as it is the drag in the water that the propeller is chosen for, the rest is just a waste of fuel.
I consider it stupid to make an engine full race as it is far more likely to be unreliable. As Harley owners say - 'there's no substitute for cubes'. Likewise, always fit a more powerful standard engine which will be almost bomb proof if built properly than a full race lump of trouble.
A standard engine will get you home.

In reality, a cheap marinised car diesel is often used, as even with excess power available, it merely ensures greater reliability with minimal cost and minimal extra weight if chosen sensibly. To keep revs down, the engine can be slightly over-propped so it works best at lower revs.
With modern alloy diesels, the weight of the engine should be a minor problem.

Even with new engines, many power boats seem to break down, often through stupidity or lack of knowledge by the owner. Perhaps not bothering to replace fuel filters regularly or dirty fuel, or water contamination. Failure to check the gauges as they go full throttle after leaving the navigation speed limit (if they can wait that long), or an inability to understand how to solve basic problems at sea, such as an inability to hand crank a diesel when the battery goes flat or fixing a simple fuel blockage.
( I know of boat owners who run out of fuel, even failing to carry a compass, and are found by chance when the mist descends,- they were motoring in the wrong direction from Eddystone in mist and rapidly running out of fuel. It happens all too often, and they are locally referred to as prats or 'boaties'.)

Making a boat engine reliable is vitally important, especially if the owner has no engineering skill or those who hire it have no common sense. Even if you don't intend to hire out your boat, you should still make sure it's totally bullet proof and the engine will always work in all circumstances. Always fit a limiter so the engine remains reliable.
Calling out the rescue services through stupidity is not acceptable.
( One rescue crew member told me of a 'boatie' who called the rescue services because he 'did not know how to find his way back into Plymouth harbour'. Yes, they do exist. You may end up towing them back into harbour, and invariably using your rope because they don't have any. - Whether you take them the easy way back or not, is up to you, but if you can put them off boating for life, then you are probably doing them, the rescue crews and the rest of us a great favour :) )

Make sure your engine is bullet proof.
As no engine is perfect, make sure the solution to all possible problems is easily to hand and easily solved. Always check the oil level. Double up on fuel pumps, or add a backup electric pump if the fuel pump is mechanical. Add a second fuel filter and a water drain trap to the fuel tank. Double up on all electronic ignition systems which must be fully waterproofed and air cooled, and add an isolator key to the secondary battery. Always have the diesel hand crank mounted securely beside the engine, preferably painted bright yellow and tie wrapped in a safe position. Have the means to pour cooling sea water into the engine should the cooling system fail. Always have a backup hand bilge pump and a plastic bucket. Always have the proper tools at hand - not in the garage at home.
See also winterising boats in the 'boats' monograph on my website.
(Bucket Tip: When using plastic buckets at sea, (minimum of two), the handles invariably break. So always add a secondary rope handle should it be needed if bailing out and you don't want to stop. The longer rope handle also helps when leaning overboard to fill with sea water for slopping down and general cleaning.)

Some just check the liferaft is there and hope their mobile phone works.
Most people prefer to be safe before they leave harbour.

The choice of engines is wide, from frantic revving two stoke gas guzzlers, to super economic, almost lethargically turning diesels. From 30 cc two stoke outboards through economic four stoke petrol, to racing Italian V12s. From the ever reliable humble diesel, to the two stroke semi diesels of genuine working longboats which may run for months and the turbocharged and supercharged two and four stoke monsters powering supertankers across the planets oceans. To this can be added vast ranges of each type, and the choice is almost limitless.
So there is always a fine choice of engine for your hull, usually at a very low cost.
As the EU bureauprats kill off our British fishing fleets, then even larger motor boats have options of second hand marine diesels and power trains :(
Just say NO to Europe.

The smallest engines are the likes of the Seagull outboard motor and their modern, even lighter equivalents.
(One of my all time favourite designs is the unpretentious British Seagull. Mine is modified with a Honda C90 CDI and flywheel, so it charges its ultra compact electric start NiMh batteries and any navigation lighting for getting out of moorings at night. A cord pull is also included, even though the C90 CDI (and its spare) is totally bomb proof. )

The smallest fitted engines are merely manoeuvring engines as used on ponds or small yachts needing to enter harbour in still air and slack tides.
In many modern yachts, there is a small inboard 'sea hole' to take the outboard just forward of the transom and makes one outboard work for both manoeuvring engine and a (rather overpowered) mooring dinghy. The ability for an out board to turn through almost 180 degrees makes manoeuvring far easier, and almost acts as a rear side thruster. When lifted, also cuts down the drag of an otherwise fitted engine. Making an outboard turn 360 degrees is easily possible if you need impeccable manoeuvring or if it's to be lowered through a tube and bottom hatch of a large sailing yacht.

For small or working boats, such as a narrow 22 footer then a small diesel is perfectly fine, possibly a two cylinder marine diesel about 500cc, such as a Yanmar 2G with marine gearbox and a car alternator and little else. Such a motor is perfectly good enough for many hours of constant chugging in all weather. Such a motor can run on a litre of diesel an hour and often even less. The Yanmar twin cylinder diesel in the picture is in a working boat that's nearing its last years and getting ready for the scrap yard, yet this original motor is still as good as new. Starts instantly, first time, every time. The alternator is a free scrapper off a Ford Fiesta.

Most boat owners can have a full days fishing in the English channel for just a few pounds and do this every day without any hassle of worrying about being able to afford more than one run a week that so many other boats suffer because they guzzle fuel.
Be sensible and enjoy the sea.

Up from the single engined sensible day or working boat is the glass fibre fancy hull, with either one or two outboards or Z drives.
A day out on a gin palace can cost a hundred pounds in generating pollution, plus bow waves that everyone else hates.

Z drive is an internal engine but with an 'outboard' style drive. These are often found on psuedo racing boats for 'boaties', and are basically designed to drink fuel and annoy everyone else. The technical advantage is that the propeller can be tilted for maximum speed and turned for better manoeuvring ability.
(Boaties also make good entertainment when they get things wrong, and may often be watched drifting for hours by those who they annoy, yet can help - (but not too soon). Perhaps the 'boatie's' boat will start to sink and they can be picked up soon afterwards, then go home and preferably find another hobby to annoy their friends instead.
Binoculars and ship to shore radio are always useful in the tourist season and can offer lots of fun, so you can 'help' these prats, plus of course, save a 'shout' for the rescue services. )

For more sensible boats, such as a day cruiser, which prefers to actually go somewhere in a sensible manner, often for many days or even for weeks without refuelling, then it is very common to use an old car diesel engine and marinise it for minimal cost.

Because salt water will corrode an engine, most engines are either marinised or use an intermediate cooling system.

Marinised engines may be designed to use sea water directly in the engine for cooling, but the internals are carefully designed to ensure the salt water does not corrode the internals. The alloy parts of the engine are anodised internally while all other parts are made from stainless or are coated with protective layers. The marined engine using direct sea water cooling is designed to accommodate the greater differences in thermal expansion and long tern corrosion problems.
For example, a basic marinised car engine will have the internal water galleries shot blasted, then epoxy coated or anodised if an alloy block. Any wet liners (cylinders) will be copper or nickel plated on the outside so the sea water will not corrode them, and the water systems redesigned with a drain at the lowest point, so it drains down after use. The original car water pump is removed and a separate sea water pump with bronze body and rubber vanes is mounted low in the engine compartment, connected via a Vee belt. The exhaust pipework is also modified to accept the cooling water. In reality more is done, but is dependant upon the engine design.
Thus a marine or marinised engine can happily pump sea water around the cooling channels with no problems other than a screen to preclude debris and seaweed etc. When not being run, the pump stops, the sea water in the engine drains down and even if the air temperature drops below freezing, the engine is quite safe from frost damage.

In most cases, such as a day cruiser, then a car engine will not be marinised, but employ a secondary cooling system added to replace the car radiator. This also allows the hot water in the engine, controlled by the thermostat and pumped by the car water pump to heat the cabin on cold days.

Because the sea water is at a much lower temperature than a typical car engine cooling system, then less coolant flow is actually needed, (unlike a car which has a limited amount of very hot coolant which demands a radiator and high flow to keep it cool). Therefore a marinised engine need only pump low volumes of water. The cooling water exits via the exhaust to both cool the exhaust and to ensure the user can see that the water flow is reliable.
The sea inlet is carefully chosen, so the motor can still drain down when beached or at rest, so that no sea water will be in the engine to freeze or cause damage. Therefore the sea water pump must be designed when running to initially purge air from the water cooling channels when started, and the exit cooling water therefore exits at a high point in the engine.

If a sea pump should fail then it will either block, or fail to pump. If it fails to pump, then sea water can often be poured into the engine from a high point, ensuring it can flow to cool the engine and may drain down past the pump to the sea. If the sea water pump is blocked or fails to turn, then keep an eye on the engine temperature, or look out for steam, and only use the engine for short times, while topping up the engine coolant system to get you home or a nearby safe anchorage.

In most cases, having to marinise a standard car engine is difficult and therefore an intermediate cooling system is normally employed. The engine may be a standard 1000cc to 1800cc car diesel, or larger if deemed necessary, but larger is rarely worth the effort unless you have money to burn.
If a planing hull which needs to get up to a planing speed before the engine can be eased back, then the engine will need to be carefully chosen according to the horsepower, without being too heavy, but with an extra amount of emergency power for poor sea conditions, then carefully matched to a semi-racing propeller.

The cooling system of a standard car engine is designed to run with fresh water and antifreeze, with the car engine water pump doing its own thing with the sealed fresh water in the engine. The heat transfer to the sea water will therefore need an extra coolant pump to pump sea water from the sea and across an intercooler which then cools the separate engine coolant. The intercooler is usually just a set of pipes in a waterjacket, so the engine heat can transfer to the sea.
Never fit the car radiator or substitute device in the water as this will cause drag and purging problems and it is never strong enough to handle marine environment, either in strength nor corrosion resistance. Any external leak or damage will render the engine almost usless. (An option would be to make a large stainless steel flat plate to match the curves of a predesigned boat hull with suitable recess, which then takes the place of a radiator, but the engine pump may not be able to handle the difference in water height if a large boat. Alternatively, if the car engine as at the rear of a boat, such as a V drive, then a stainless cooling system may be run in pipes off the rear of the transom, but will need to be cleaned regularly or Teflon or anti fouling coated or scrubbed regularly to prevent overheating.)
The sea water pump is normally driven from the engine and as such, the belt or chain drive will need regular maintenance. Once again, because the sea is always much cooler than the engine, the sea coolant flow will be less than a normal car engine coolant flow. Therefore the intercooler will be passing high flows of car coolant whereas the sea pump will pass lower volumes of much cooler sea water. If the engine side of the intercooler is about a toasty 80 degrees, and sea water is about a cool 10 degrees, then only about one eighth the amount of sea water is needed to dissipate the relative amounts of heat. (Approx.)
Such an intercooler can be bolted to the side of the engine, or mounted in the hull, depending upon the position and type of sea water pump.
In emergency, the engine can be cooled with sea water to get home, but must later be flushed fully to prevent corrosion in the engine.)
An engine water temperature gauge is nigh-on mandatory and very easy to fit. Especially recommended where seaweed is prevalent.

DIY intercooler. To make your own basic intercooler, make up some lengths of (corrosion resistant) copper domestic heating pipes, soldering them to fit into a compact plastic or stainless container, such that the copper pipes connect with rubber hose to the car's sealed engine coolant flow. I simply cut the pipes all the same length, apart from the top and bottom ones which extend outside of the cooling chamber. Fit U bends, then array them so the bottom one takes the inlet and then gradually work their way up the pile so the upper one is the exit, and so that all air can safely purge out of the system and all the engine coolant can drain down easily if needs be. They are then packed closely together with packing pieces of cardboard to separate them by about 1/4 inch, checked they will fit inside the cooling tube, then soldered up. Make sure the air will naturally bleed out of the system, with no hidden air pockets. The copper pipes can be fitted inside a sea water coolant chamber, such as a large plastic drainpipe, as the heat is minimal and pressure even less. The end caps are modified from the standard plastic drain connections, and glued to accept the sea water flow from the sea water pump. Therefore only two joins are needed for the inlet and exit of the copper pipes, and two connections for the sea water inlet and exit. The sea water exit is highest, to vent out near the exhaust exit, so the sea coolant flow can be checked. Lacquering the copper pipes or fully 'tinning' them with solder can prevent undue corrosion. By using long lengths of domestic piping, and plenty of U or 90 degree bends, a very compact bank of copper pipes can be fitted into a large plastic water resistant drainpipe. The heat exchanger can be angled slightly to ensure that all air will vent naturally from the system.
The sea water pump is usually a bronze body design with synthetic rubber impeller, and belt driven from the cranskshaft. Never use a duct under the hull or an inlet pipe near the propeller to push sea water through the cooling system, as it can easily be clogged or broken, or the engine may be turning over while at rest and thereby overheat.

As sea water is not guaranteed pure, debris can accumulate in the system so a screen is placed between the inlet hole and the heat exchanger. Any sea inlet into the hull should ideally have a sea valve which can be securely closed in emergency, or for maintenance upstream or for winter mooring. At least have a wooden bung specially for the purpose and mark the position on the hull when bobbing alongside in the dinghy or dangling on a rope.
The sea water inlet to the engine cooler should include a sludge trap consisting of a wire screen to remove unwanted sea matter before it reaches the rubber vanes of a sea water pump. The screen should be easy to extract and clean after the sea valve is closed, or if no sea valve on a small craft, then simply removing the screen and fitting a temporary wooden plug. For greater ease, the screen can be such that any debris will naturally fall down, out of the hole when the screen is not in use. Additionally it is possible to have a rotating or plunger screen wiper device which uses a simple lever operated from inside the boat, to scrape the screen and allow excess gunk to be pushed or drift back down into the ocean.
Inlet screens often get clogged and will need to be cleaned manually. To do this when afloat, it must be accessible with minimal hassle, so a replaceable quick-change screen is used. If no sea valve, then being able to replace the top before too much water enters the bilge or in a compartment which has sides above water level. I prefer a simple quick removable screen, which can be replaced as a cylindrical perforated stainless steel tube inside a larger T piece with easily removed cap which takes a few seconds to replace. When making your own, just make two, so one is cleaned and ready for a quick swap for easy maintenance, or when the engine begins to overheat. For larger engine systems, then an inspection plate can be added, such as a piece of Polycarbonate riot shield set close to the screen or set in the screw lid. This allows the crew to check the screen before problems occur. Always carry perfectly shaped wooden bungs very close nearby for when things go wrong. If you can make a large rubber sheet on a long curved stick with a small tapered plug which fits neatly over the inlet when leaning over the side, then this can make replacing the screen easier if you sail in dirty or unsafe or infested waters.

Mounting the sea water coolant pump is often done using a Vee belt to a bracket on the engine, but check the working revolutions, so the pump runs as intended. Secondly, make sure the pump can be easily maintained and the rubber impeller replaced without hassle and the Vee belt easily adjusted. Unfortunately, because car engines are not always designed for a second pump, as well as the alternator, then some home made bracketry will be necessary. Modern car engines often have mountings for air-conditioning or power steering, so these can be used for the water pump mounting.

An advantage of metal hulled motor craft, is that the engine cooling system could be integrated into the keel areas, so that the engine coolant can be inboard, against he hull to keep the engine cool. This reduces drag, and has no need for a separate sea water pump. Such a keel cooling system will need a well designed cooling area, such as a large coolant space against the hull, so the heat can be exchanged into the sea water. Some minor distortion may occur from the heated water. Similar systems can be integrated into non metal hulls, of a suitable flush fitting space is designed and maintained.

Mounting vee pulleys to shafts is fairly straightforward, where the builder simply chooses the Vee pulley for the pump, to match the desired speed for the crankshaft pulley. Often crank revs, so a 1:1 ratio in pulley sizes is simple. Where the Vee pulley does not easily mount on the pump or crank flange, then the old pulley is ground down to keep just the bolt mounting holes and then the new pulley welded to it. Lightly glue the pulleys together at first, then check the pulley runs true before welding it properly.
Where you wish to fit the power steering pump and air-conditioning pump, then the other side of the engine may use the alternator Vee pulley to drive the water pump, by using a longer Vee belt, and an intermediate jockey pulley between the alternator and the water pump pulley,, so the vee belt has at least 60 degrees of wrap on each of the pulleys. A jockey pulley consists simply of a sealed ball bearing rubbing on the back of the Vee belt, and retained on a pivoting bracket and an adjuster to maintain good belt tension. In some cases, the jockey can be held by a spring. An adjustable compressive spring design would be safer for long term reliability.

Always carry a spare sea water impeller, gasket and any drive belt. As these pumps are often hard to reach or near the bilge, replace any rotor plate retaining studs and nyloc nuts with longer stainless steel versions painted bright yellow so that replacement is much easier in an emergency. Always heavily grease these bolts and studs with graphite and copper grease.

If the marine engine has a water-cooled exhaust manifold, then drill a 5mm hole in the flange of the thermostat, so that some coolant can flow from the outset, to prevent the manifold from boiling its liquid contents.

Apart from any marinisation, little is done to modify a standard engine, other than to make the usual checks to ensure it's a decent one. Only a modified lower oil drain hole or sump syphon pipe may be needed, which does not need stripping the engine. An engineers stethoscope is available for a few quid. Check the oil and water for excessive contamination. If all is well, carefully clean through the engine and remove the (engine) water pump, to power wash the water jacket, without removing the head if the compression readings are OK and the donor car has not done too many miles. Always refill with fresh water and anti freeze. A car engine being used in a boat is normally revving at a steady state and thus settles down with minimal wear and temperature change, so the rings, bearings and such like suffer far less wear from a constantly accelerating and decelerating car engine. (A sort of easy retirement for the engines' last decade or so.)
Always replace any cam belts, oil, oil filters and air filters, then set the engines' hours of use counter.

In a new, small hull, it may be possible to place the engine in the bare floating hull and move it fore aft slightly to get perfect balance. This is not always possible, so keel ballast, fuel and water tanks and such like are later used to balance the boat perfectly for optimum cruising alignment. If a racing hull with minimal accessories, then engine balance is paramount and may often need modified drive trains to become perfectly balanced.

Make up suitable engine mounts to align the engine perfectly with the propeller shaft. There will be an intermediate coupling between gearbox and prop shaft, and perfect alignment is always recommended. In such cases, the motor will often be a little nose-up, but this is not a problem once the correct oil level is decided and any potential air blocks in the cooling system are overcome. Even cars have to drive up long or steep hills in the Alps.
The rubber mounts of the engine should be specialist items which deaden most vibrations, but do not cause misalignment. A head steady is often used for the start up torque problem. If torque is a problem, such as power boats where the throttle is often adjusted, then always mount the flexible parts of the engine mounts evenly spaced directly opposite of the centreline of the crankshaft. I like to sit my engines in three rubber mounts, a pair spaced far either side of the coupling to take the torque and remain perfectly aligned with the prop shaft coupling, and one rubber support forwards to adjust angle. Most boats use four evenly spaced rubber mountings.
Even where the engine bay is pristine, of fuel or water is a problem, then the rubber mounts should have an oil or water deflector to keep them dry and reliable. I often adapt upside down small stainless steel saucers or bowls.

If for example, using an all alloy Jag V12 EFI engine, then the two main engine mounts are mid point and are ideal to take the weight and torque, plus using just the one modified rear gearbox rubber mounting to perfectly align with the prop shaft. Vibration is not a problem, as V12's are really smooth and a delight to work with. I prefer to cool such racing engines with sea water to save a lot of weight and reduce engine drag, but they must always be fully flushed with fresh water after every race. Letting them 'drain down' is not good enough. Remove the thermostat, fit the fresh water pipe to a modified thermostat housing and flush for two minutes.

No matter what engine, from a simple 2 cylinder diesel, to a racing monster for a mad customer, later, during sea trials, it may well be worth while to 'tune' the engine mounts for the most silent running. The constant drumming sound of a motor boat can be greatly reduced if the rubber engine mounts can be tuned. Slightly tightening or loosening, or carving back the rubber of larger mounts to get the smoothest running engine with minimal stress on the prop shaft drive and minimal vibration entering the hull.
Submarines and Naval ships spend plenty of time on sea trials to ensure their hydro acoustic profiles are minimal.

Gearboxes. These are often used on car engines with a marine gearbox bolted on the end.
Driving through water will not offer the shocks of road use and the car clutch can be left unused in the fixed position. Just make sure the diaphragm spring is epoxied to prevent it rusting and finally causing the clutch to slip. An old clutch plate can also be epoxied in place for further reliability and to ensure the friction material does not corrode over many years at sea. Reverse in a car gearbox is slower and the engine may well ove-rev, and never offer any real astern speed, so should only be considered for manoeuvring.
Although extremely rare, a car automatic transmission also possible, but tends to be less efficient unless wanting smooth planing speed or high reverse speeds. Always include a transmission oil cooler and choose a modern, efficient auto trans.

Because the engine is in the bowels of the hull, then oil changes by draining the sump is often impossible, as most builders will want their propellers as horizontal as possible and so the engine is mounted as low as possible. Therefore the sump drain is sealed, with a secondary oil drain pipe and suction pump to suck up the oil and also any debris that has accumulated. This is usually done by making a hole high in the steel sump then adding a steel suction tube down to the lowest part of the sump. If a steel sump, then simply drill a hole through the steel, above the deepest part of the sump, and drilled preferably above the oil level. Insert a bar the same diameter as the intended tube, and bend the steel sump slightly so the pipe will reach the lowest part of the sump. Then inspect with a torch to ensure the pipe will not foul any internal components such as crank or con rods. The pipe can then be soldered in place. The tube should be thick walled to reduce vibration and reduce chances of subsequent fracturing, and extended and supported on the engine with a bracket. The bottom of the pipe should touch the bottom of the sump, then lifted 1mm before soldering, so the oil can be drained fully. The end of the tube should ideally be soldered inside to prevent vibration fractures and must never get close to any moving parts. If an alloy sump, then an adapter can be made to fit the drain hole and a suitable suction pipe added. I prefer to make slightly larger drain plugs and add a banjo side pipe. The suction pipe must be high quality anti vibration plumbing. (I use Goodrich hose for reliability.) A simple vacuum pump will be needed to remove the oil. A modified push bike pump is common, just reverse the piston washer and add an upper drain hole.
The oil filter will normally be well positioned, with a simple working space or elbow room around the engine is usually all that is needed, if it can be fitted easily, then it can be removed and replaced without hassle. Just make sure you can replace all common parts while in situ, including the cam belt, or chain, pump and electrics.
It is vitally important to choose an engine with a gear or chain driven camshaft, as belt drives are rarely appreciated in the boating world. They may serve perfectly in the world of tarmac, but not so well in a marine environment. For true reliability, chain or gears remain the best choice. If you use a belt, then you must always include number of hours run counter for the engine, so that maintenance is reliable, or be prepared to change belts yearly. If changing belts of a modern racing engine, then ensure there is plenty of room and preferably modify the belt covers and add bright yellow timing markers on the toothed drive pulleys. Changing belts should take an hour or less. It is highly recommended to add a number of hours run to an engine, as this tells you of the optimum maintenance if used daily. (See the 'boats' monograph wiring.)

A good engine is easily maintained with minimal cost other than an oil change, air, oil and fuel filters and check the ignition, and valve clearances. Standard yearly engine maintenance should take an hour and cost under fifteen quid for an average engine and include any valve adjustments, oil and water changes, oil and air filters, and checking the stern gland. (Spark plugs optional if petrol.) Fancy engines can take a day or two.

Because the engine is in a potentially salt water bilge, then a really good quality paint job is recommended, then waxed to ensure nothing gets rusty or goes amiss. The rubber engine mounts should be shielded and also waxed or covered with rubber paint to help reduce ozone deterioration with time.
Aligning the engine with the propeller shaft will depend upon the connection, but the prop shaft will be projected to ensure the engine mounts into the hull are perfectly parallel. The alignment can then be adjusted with shims under the engine mounts until both run perfectly concentric. Primary alignment will be done at the design stage, with final engine support bulkheads and fitting done with the engine ideally positioned in the boat. Always allow the engine a little more clearance then expected at the design stage, as a different or replacement engine may need more bilge clearance to get perfect alignment with the prop shaft and enable a fairly horizontal propeller alignment for optimal efficiency.
The gearbox to prop shaft connections should be electrically isolated to reduce electrolytic corrosion. Therefore they are often rubber dog drives or a similar method of coupling. This also helps reduce engine damage if lightning occurs.

Where the prop shaft enters the hull, there should be a drain area to allow easy inspection of any leakage before it gets too bad, so a bright yellow or white bilge paint in this area is recommended, with easy line of sight for regular inspection. (In a few increasingly rare designs of wooden hulls, the bilge is deliberately 'wet' where a bilge pump used such that the wood remains wet and thereby more watertight, whereas dry planking can shrink. All wooden boats are 'sunk' before their first sea trials.)
Where the engine is mounted close to the hull, then this should be spread across the hull broadly to dissipate any stress. All main structural reinforcements should be considered with the engine in mind. Cross bracing from the main interior beams can then support the engine. Strong, water protected wooden beams are perfectly adequate and final protection with clear lacquer will show if the wood is being compromised over the years from water ingress before it gets too bad, otherwise, welded steel beams can be used. (Preferably galvanised.) For ultra lightweight power boats, a diamond beam may be needed to handle the torque.
It is unlikely that the owner will allow junk to be swilling around in the bilge and cause damage to the engine, but if such is the case, then the engine compartment should be sealed from idiots.

To the engine compartment are often added other bits such as sound deadening materials over the inside of the engine housing, especially if a noisy diesel or a large engine. This is often just fire resistant foam lightly glued to the inner surfaces, but does not reach down to the bilge area. Engine deadening materials and coverings can be added if needed, and the best source of info is from the ministry of transport research labs, which conducted studies on lorry engines and this is also applicable to marine engines and recommended for gentle, quiet cruising, especially in inland waterways without upsetting the wildlife.
On motor boats, it is often worthwhile to fit an engine bay vent, consisting of an air duct pipe into the exhaust line such that the movement of the exhaust also extracts any unwanted fumes building up in the engine bay. This must NEVER be used for venting domestic spaces, but purely for engine vapour and gasses. The pipe is simply venturied in the exhaust pipe, near the exit. If fuel injected engine, always do this far downstream of any lambda sensor or catylicitc converter.

A fire extinguisher should be easily reached in case of an engine fire.
Larger boats should be fitted a dedicated fire system, where any excess heat or flames will activate the fire extinguishers, to automatically put out any fuel or electrical fire. Some of the better systems automatically close the fuel lines too. For most purposes either foam, powder or CO2 is used. CO2 works best in a sealed engine compartment, where there is no room for people, with the air vent at the top, as CO2 is heavier than air and needs to displace the oxygen in the compartment with minimal fuss and no mess. Foam or powder can be used where people may be present.

If you don't have a fire extinguisher easily accessible near the engine, then you are a fool.

Always remember that engine compartments will soon become an oven if the heat is not controlled. The exhaust system header, which bolts to the cylinder head is often water-cooled to keep the engine bay temperature under control. If not water-cooled, then the exhaust should be lagged to keep engine bay heat to safe levels. The heat generated by the engine may not always be able to be passively cooled by an air vent at the top of the engine compartment, to let the hottest sir to escape and cooler air to circulate naturally. If the engine bay is sealed, such as in a motor yacht, then some form of sealeable upper vent or hatch must be considered to allow constant motoring to be safe. Heat build up in the engine bay can lead to fire on board, possibly because of a fuel leak and an unfortunate electrical fault. The heat in the engine bay simply helps fire to happen much easier.
All engine bays should be very carefully considered to keep the engine bay heat to safe levels.

The exhaust system, being hot, should be ducted and insulated, with the sea water coolant discharge to help cool it. If a low exhaust, always add a flap valve so that sea water does not work back to the engine even if suffering a heavy list. In larger engines, the heavily lagged exhaust normally runs along the deckhead to keep engine room heat to a minimum, and to ensure any sea water will not get back to the engines easily.
Some exhausts exit under water to restrict noise and therefore should be carefully routed to prevent water returning back to the engine. Wherever possible, the exhausts should be over a suitably sealed bulkhead to prevent sea water intrusion between watertight bulkheads if the hull is breached.
The exhaust must be lagged to prevent excessive heat entering the boat. This is normally done with dry glass fibre cloth wound around the exhaust and retained with adhesive aluminium tape. If this becomes loose, (from a rough engine) then some baling wire or mesh as well. Where the exhaust exits the hull, it must be vibration proof, yet totally waterproof, and away from injury with swimmers. The exhaust is usually mounted high through a bulkhead using a special synthetic heat resistant rubber tubing for vibration and water tightness. Any such seals should be inspected and replaced regularly.

In larger boats, especially large motor 'yachts', it may be important to add a separate generator and motor (which is often just a stand alone building site generator.) This can be hidden anywhere or in the engine compartment, and is usually rubber mounted for silent running while at anchor. A 2500 watt 240volt AC item with 6HP four stoke motor can be bought for under 200 pounds. An alternative is to use a bank of car batteries and inverters which are charged up when running.
Any fancy or expensive electronics such as with fuel injected petrol engines, then the control box or boxes should be rubber mounted somewhere dry and cool, and if needs be, in a separate compartment or in the air intake flow to the engine compartment to keep the electronics cool, but dry.

Motor ancillary components.

When designing a fuel tank, always work out the fuel consumption of your craft and expected longest journeys, then add 100 percent extra for emergencies. It is possible to buy plastic fuel tanks for moderate use boats, and the selection available is reasonable and can be fitted into a range of compartments.
Larger integral fuel tanks are often near the keel with a bulkhead between the fuel and the engine compartment. Having two fuel tanks suitably plumbed, will ensure that any leakage and a happy bilge pump, will not leave you without fuel.
Making your own fuel tanks is fairly easy if making them in steel sheet, as available for repairing car body panels. Always include anti slosh tanks and get the welding only tacked in places, then hand over to a professional mig or oxyacetylene welder. All fuel tanks should have pressure vents and drain areas to catch the sludge and water and should be easily and safely drained. The vents should be via a filter to fresh air, and putting a small paper element fuel filter in the line helps prevent contamination and flash back. Always include a wire mesh flash arrestor - even use steel wool stuffed into the vent hole on toy boats if the owner has none. (You'd be surprised what I carry in my tool kit and their purposes.)

If deciding to use a small compartment in the hull for direct fuel containment rather than a separate fuel tank, then always fit a hand hole to clean out the tank or chamber and have it securely held in place with at least four bolts and a synthetic rubber seal. This will allow regular cleaning, inspection and occasionally resealing the fuel chamber. Special fuel tank sealer is available. Wooden hulls should always have a separate steel or plastic fuel tank.
On power boats the fuel tank should be fully rubber mounted to prevent wave vibration and slamming which can cause cracks and leakage.
Always pressure test and inspect after a long or hard run.

Fuel gauges are very easy to fit but should be in a small baffle compartment to prevent excessive sloshing causing excessive wear. See my boat wiring and bike wiring monographs on this website. Dipsticks are most reliable or a level gauge is also recommended, because electric fuel level sensors tend to get a very rough time at sea in day cruisers and in racing craft.

When designing a lightweight power boat, then the fuel may be a large percentage of the overall weight, and therefore needs to be carefully balanced or positioned in the centre of gravity of the hull, so that any change in mass as the fuel is wasted used up, will not upset the overall balance of the machine.
If for some obscure reason, you choose to use petrol for a marine fuel then you are either wanting to go fast or are daft or both.
If the fuel pump is a mechanical device on the engine, then check the long fuel tank run is acceptable, and the fuel level is similar to that of the original car placement. Some pumps are a long way from the fuel tank, and if the fuel tank is much lower, then the pump may not be adequate. If an electrical fuel pump, always include a secondary pump and add fuses.
There are two types of electric fuel pumps for ordinary car engines. One about three psi, the other about six psi. The low pressure type is for a pump mounted near the carb. The high pressure pump is used when mounted near the rear fuel tank of a front engined car and probably the better choice for larger boats.
Connect any electrical fuel pump on the ignition circuit so it will not pump when not needed. Use a separate fuse, because pump contacts occasionally weld themselves together. Spare contacts are normally available for decent electric fuel pump and should always be kept nearby in a waterproof bag. Preferably buy a second car fuel pump from a scrap yard, and plumb it in parallel with the primary pump and a simple electrical switch over if one should fail.
With two fuel tanks with gauges and pumps, then a simple switch will allow the pumps to change over to maintain good trim.

If making a racing boat using petrol then carburettors are acceptable, but to eliminate carb float troubles, then chose a fuel injected engine to eliminate this unwanted variable on rough seas.

Fresh water (drinking water) tanks.
Fresh water tanks must always be meticulously cleaned and maintained, preferably food grade nylon or polyethylene. (Polythene) They should ideally be removable for inspection and regular cleaning. Drain each season and thoroughly remove debris. Then sterilised with water additive such as a little chlorine and dried out, ready for the next season.
When building such tanks into the hull, they should be lined with epoxy. Also include access hatches for full cleaning. On some of my special builds, I like to line fuel tanks with thick aluminium foil epoxied in place to reduce contamination, as aluminium helps reduces long term damage, especially to a fibreglass or ferrocement hull.
Where possible, consider a water maker, desalinator, driven from the engine or using 12 volt motor to ensure fresh drinking water. PUR watermakers offer a fine range of options. Manual desalinators are also available and should be used as a back up, plus a small one for the life raft.

Waste.
Along with fuel and fresh water tanks, must be added another important storage area, - for rubbish (trash).
Rubbish storage compartments smell, so should be part of the upper deck compartments, usually under the decking in an otherwise dead area of the hull. Choose a place where the rubbish can be easily compacted such as plastic and metal bottles and tins. Kicking a tin can flat on deck then throwing into a nearby smell proof hatch is recommended. Try not to have old milk or other food stuffs casing problems, by using a separate bin bag storage area with removable waterproof tubs. Biodegradable food waste can be safely dumped overboard if more than five miles off shore. If in harbour a lot, then use a separate bin for food waste. If the rubbish compartments are fitted with large removable plastic tubs, then they are much easier to handle for disposal on the harbour, and also much easier to clean and freshen for the next journey.

In Plymouth, many boaties on their gin palaces dump their sewage and condoms and rubbish overboard even when in harbour. I still expect to get ear and nose infections every time I have my first few swims in the sea hereabouts. We all hate 'boaties'.

Control: Fancy vs effective.
Sad but true: The steering position of a gin palace motor boat is often an ego boosting plethora of fancy shiny dials and such like.
There is a pathetic tendency for power boats to have overly impressive throttles as if they were some form of fertility symbol. Any engine needs just a simple friction throttle lever and a gearbox lever for forwards, neutral and astern. If a Z drive then perhaps some tilt adjustment.
Very little is actually needed and engine controls can be discretely hidden, other than a very simple throttle and an engine stop button. For stopping diesels, then a cable is often needed to pull the fuel pump stop lever. In heavy seas, a lever is not a good idea for throttle control and I consider a simple rotating knob makes for a far better throttle control device, especially if rolling badly and it is out of the way from being nudged by accident.
For small boat engines using simple Bowden cable controls, a very cheap push bike gear change lever is perfectly acceptable. They have adjustable friction pivots and can fit almost anywhere and ideal for yachts with an auxiliary engine. When recessed into the control panel, they are almost fool proof, even in high seas.
Gearchanges from F-N-A, can be accomplished by a separate and simple locking lever or which is sprung into one of three slots. These can be tucked away almost anywhere, such as in the corner, where they won't be nudged by accident.
For those who are not trained or mechanically minded, a specialist throttle needed, which puts the engine into tick-over first, then into neutral before going astern. The common engine and marine gearbox have simple levers and therefore can use simple controls.

Instrumentation for engines and boats is usually a selection of more sensible dials for water and oil temp, oil pressure, volts and such like, all available from car scrap yards for pennies and in any shape, style or colour you wish. I occasionally open standard gauges and paint or print new dials to match the rest of the machine.
A rev counter is used if a racing engine, or if housed in a silent compartment, otherwise your ears are perfectly good enough. Along with this are the oil pressure, either a warning light or a pressure gauge - preferably both. The water temperature gauge and charging voltage. (Voltage is often also shown on echo sounders and other secondary devices.) Fuel gauges are also found on many boats, although not always included.
On ocean yachts, it is often necessary to include repeater devices inside the cabin when using an auto pilot so that any warnings or changes can be reacted to when taking cat-naps or preparing a meal.
Instrumentation for engines and boats is usually available from the manufacturer and may cost daft amounts of money.
The builder may be moved to a perceived need for a large control space in the cabin or near the steering position for all this stuff. It may look good for fancy boats or those who need to be impressed for buying machines from boat shows, or want to think their boat is bigger or clever than it really is, or simply need to inflate their ego, but for real use, a big spread of dials and gauges and lights are not always needed, especially when room on board is at a premium.

Big cabin displays, big posing levers - No thanks !

Displays: I build many and diverse designs, yet always revert back to a small selection of excellent alternative display devices. I demand small, really effective displays which tell me what I need, clearly and instantly, and are easy to replace if things go wrong.

Whether a wheelhouse or open cockpit, I need my space for important stuff - charts, binoculars, - a cup of tea and perhaps a biscuit.

(Consider some clips and a bungee over the table in a yacht to stop charts from blowing around or away, especially if entering new waters. Preferably print two copies of all expected charts, should the computer or printer fail, or a chart blow away or get soggy. If staying for a few months, then laminate the chart. Ask at larger sailors haunts and ports, as commercial ships must update their charts yearly and may have old charts of the area for sale or for free.)

An example of a pragmatic approach: A typical aftermarket motorcycle LED screen is not only cheap, but also waterproof and contains rev counter, speedo, fuel gauge and volt meter etc. They are easily adapted and include adjustments to match accurate readings. The generic device shown here, which is quite cheap to buy, has an analogue tacho, digital speedo (log), voltmeter, fuel gauge, overall distance travelled, an individual trip, clock and back light.
The bar graph display is used for the rev counter, the digital display for knots, (these items are very adjustable to fit almost any machine) and the other bits and pieces integrated into the design offer all you may ever need. E.g. the overall 'Riding Time' readout on this standard model is ideal as a substitute for 'hours run' meter for the engine of a motor boat. Around the bezel are oil and other warning lights and the clear and easy waterproof operating buttons.
Such devices are not only waterproof but also very lightweight, compact and run off 12 volts or on small batteries which need next to no power and easily powered by a baby solar cell. Ideal for full boats to test rigs, even one man yachts.
For a diesel engine, then the rev counter can be adapted by gluing a magnet to the crankshaft pulley and fitting small pulser or a simple reed switch, plus a similar device for the speedo reading to give a log in knots.
Making a log for this is child's play - a wire, fishing swivel link, prop, magnet and small reed switch is all that's needed. These units are adjustable to accept a wide range of pulses and convert them to accurate readings. (See easy CDI ignition on this website.)
For example, if on a yacht with composite mast using integral strain gauges, then the analogue tachometer bar can be switched over from the engine tacho and used to indicate the strain on the mast, or as a wind speed meter from an anemometer on the top of the mast. So easy.
The speedo counter gives a bright and clear water speed log. These LCD screens are also very easy to read in all lights, have back lights, and are far neater than a plethora of many tacky gauges.
Tucked neatly beside the control station, the master has all that is needed, leaving lots of room for the other bulkier electronics. Another identical repeater unit can be on each side of a yachts cockpit, another added in the cabin and a spare stored safely for an emergency 'hot swap'.

On very small boats, even the most humble kiddies push bike speedo / computer offers more data handling than is needed, and all for under five pounds.
The disadvantage of such devices is that they need electricity, but a back up battery is included to retain the data for a year or more. The push bike devices are even better and ideal for small yachts, as they only need a single cheap button battery for a year of use, and that includes powering the reed switch speedo (log) sensor. When a couple of micro solar cells from discarded calculators are added, then such devices are incredibly cheap and totally bomb proof.
For larger yachts, such devices also make excellent repeater units for inside the cabin, to keep an eye on the boat when making lunch or while cat-napping with an autopilot (see appendix).
Having such cheap devices also allows a spare to be carried and 'hot swapped' at a minutes' notice.
Never underestimate these devices.

Wiring.

Fitting out.

Lateral alignment.
Always make sure the boat never lists while fitting out, as any straight edge or spirit level should be considered fundamentally flawed unless the hull is (rarely) referenced to the horizon. So always position a perfect reference line fore and another aft when fitting out a hull. Stand on the rear centre and measure the waterline to gunwales, or get in the (still) water or the dinghy and measure them, as it is impossible to check while leaning over the edge of the boat.
Fore - aft alignment and balance.
While fitting out, the first thing to do is to fit a plumb line using a stretched cord from central bow to central stern, then use a plumb line form this stretched line, so the hull can be wedged to be perfectly horizontal when looking from the bow. All measurements can then be aligned from this reference point. Secondary plumb lines can then be made form this is f needed, although the keel line should be a good reference unless a catamaran or a twin hull design.

For most boats, the fitting out should be done with careful reference to the waterline. Unlike an aerobatic aircraft which desires all its mass central for easy manoeuvrability, or an off road motorcycle for the same reason, a boat should try to remain stable in all seas. Unfortunately placing all the mass central in the hull can cause it to misbehave in surf or steep waves, this why the boat man sits on the prow to spread the ballast of the semi inflatable craft when saving surfers. See earlier.

Ballast.
See also Keels and Keel Tests.
It is best to make a model of the design and test it by using movable weights, but this will only give reasonable and not absolute confirmation of the overall handling of the finished hull and its effective placement of the total mass relative to the displaced volume of water.
Once the boat is fitted out, it will hopefully be under-ballasted and sit a little too high in the water. This is good, as like a formula one car, you can start adding ballast as and where it makes the best handling chassis or hull.
First try to ballast the boat to sit in a similar manner to the best behaving hulls of the same type. Check carefully the waterline fore and aft, to get, not only the displacement, but also the alignment in the water relative to the keel alignment and keel design.

It is important to get the right amount of ballast, then place it for best results, then not allow any unwanted extra ballast to flow on board, nor allow the ballast to move about until you have refined its position.
At a basic level, a boat shipping too much water which cannot be removed fast enough by the bilge pump, will wallow badly and the helm will be slow to respond, similar to an over ballasted hull. If you allow some bilge water into the hull with big sponges, it is possible to assess how it handles and get a feel for the limits, then turn the bilge pump back on until it handles better. When back at the mooring, the volume that the bilge pumps out can be collected and measured, then the equivalent mass added.
If the mass of the ballast is placed with a high polar moment of inertia, like a dumb-bell, then the boat will handle slowly or be too stable and may ship too much water by not moving or flowing fast enough with the moving surface of the sea. A boat can only fight the sea to a limited extent, as a boat must learn to give.
Only wave piercing hulls can consider fighting the waves and this needs some very careful design and a specific hull shape, as used by the Team Phillips to good effect even in very rough seas.

For most boats, mainly power boats (and to a lesser extent, some day yachts which also use keels to offset the sail pressure), it is important during initial sea trials to try to get a good compromise, spreading the ballast sensibly along the keel, and veer just slightly towards the dumbbell end of the scale for general safety.
Most people just add more ballast if the boat is a bit unstable. Others may want to refine their craft much more during their sea trials.

Initial tests on the boat may include adjustable ballast, although the first test should be to check reliability and ideally done in millpond conditions, usually at the mooring or immediately after launch. Then heavily rocking the boat to see if the basic hull is too sluggish or too lively.
Secondary tests, after fettling the engine and such like should include some mild seas to see how she behaves. Where regular car ferries occur, then their bow waves can offer a constant and regular testing environment to get the overall balance as decent as possible.
Being able to pump water from fore to aft, or move weights about, such as old bricks and breeze blocks is very useful as you can test in identical conditions with variable masses of ballast.

For getting a really refined ballast, needing added ballast while at sea, it may be worthwhile to use three large plastic sea water tanks in bow, mid and stern, then use the hand pump for a day of testing various arrangements in moderate seas to get the hull to ride in an optimal manner. Three large dustbins with anti slosh lids can be used if you don't have discrete bilge compartments. Alternatively, use a few more bricks than needed to get the basic balance, then move them or chuck a few overboard as required. The advantage of sea water as ballast is that you can easily add or remove at will.

For yachts, getting the keel mass optimised is harder, but the minimum mass can be determined by the keel test mentioned earlier. After this, more weight can be added if required but this will need sliding or clamping or tying extra weights to the keel and when correct, the mass can be weighed, then a one piece lead keel cast to shape as mentioned earlier.

Once the fore - aft balance is about right for reasonably safe use, then refinement can begin.
Always remember that water as ballast will not allow the roll to be assessed, as it simply does not respond as solid ballast does.
Testing sideways on to the waves may require adding or removing overall ballast to get the hull to ride this unwanted but oft encountered effect as safely as is possible. Splaying the central ballast either side of the keel line can help slow the frequency to roll, but too much and the boat will become sluggish to return to the upright position, so always do this test in the largest selection of waves you can find.
If the boat rides badly on a beam sea, then adjust the overall volume of ballast in the middle of the keel until it rides well.
Ride head on into the wave. If the boat exhibits a tendency to wallow in pitch (nose up and down) too much then redistribute the ballast from fore and aft to the middle until it can handle waves head-on with minimal hassle. If it tends to dive into a wave, showing a slow response to forward buoyancy, then move some ballast from forward to the mid and rear. If it's too light at the front then redistribute some of the mid and rear ballast to a forward position.
Test again when stern on to a wave.
Most craft approach a wave at about 35 degrees to minimise pitch and roll.
Get to know the boat really well.
The effects on roll when side on to a wave will vary according to the hull shape which can affect the damping or not. An excellent example is a modern ocean racing yacht with thin keel with little side effect and minimal damping, compared to a traditional yacht with a deep, long keel which affords a wide underwater face to the wave or sea and much larger damping effect. Likewise the deep chine hull or a rounded motor hull will also affect roll differently and also cause eddies in the underwater areas which can stall the desired water flows, such as to affect the roll rate and the inertia.

How the designer wishes to employ or overcome these effects will depend upon use, such as a modern racing yacht needing to change direction sharply, or for a steady and easy coastal cruising or whatever may be needed.
High roll with slow response from high inertia can lead to unstable craft. The opposite also applies where a hull can be too lightly responsive and be tossed about like a piece of flotsam. This all varies upon the forward speed and the effects caused in any stalled areas of flow along the hull.

To the above can be added the rolling effect of the water particles in a wave, as can be seen end-on in a test tank. Chop up small particles of toilet tissue in a food mixer, fit a glass panel across a long bowl or pond and study your own waves and how the model hull behaves.
The Fastnet race of 1979 where the wave height of 12 metres and frequency of 9 seconds was likely to cause grief to any hull designer, when the stability of many yachts in these conditions being close to half under certain sea circumstances, where the yachts on the crest were getting close to dangerous limits and here all the good unseen design details come into play to enable better stability and control, allowing a good sailor to return safely.

When sagging, a hull is less effected to yaw, but when hogging, can be far more delicately poised. When it is often pointed into the wave to improve the situation, the rudder responds only at certain times and the various keel designs may also cause problems or assist. Try it, then solve it, - while you still can.

When all is about right and the boat has the correct amount of ballast and handles all waves as good as is possible, then finally adjust the fore and aft balance slightly for the optimum ride at cruise speed. Slight changes can be made on straight test speed runs in both directions to maximise the speed available from the cruise state of the engine.

Whether motor or sail, it is an expensive design, then standing up to your chest in breakers on a beach with a six foot model is highly recommended and will always pay off the investment in hull design and initial assessments of how to refine the hull profile, handling characteristics, self righting abilities, ballasting and other refinements.

Your pride and joy may now be taken out and tested in nastier waves, but never exceed the limits of the boat and tie the ballast tanks down if the waves start getting too high for safety as you turn for home.
If you decide to do this level of testing, then weigh or calculate the water ballast and make notes on your design sheets of the final ballast masses. Then they can be removed of tanks and replaced with permanent ballast. Make a note on the builders plate.
Before removing the test ballast, use a permanent felt tip marker noting the individual masses which must be marked on the hull before removing the water ballast and fitting secure, solid ballast.
A better option when back in the moorings, is for me to get in the dinghy and use a permanent felt tip marker pen around the forward and stern true waterline before replacing the tanks with permanent ballast. A good builder may mark this with a couple of small stainless steel points on the hull for future reference. Even after a full rebuild, the boat can then be given the correct ballast and have a rough guide to the fore aft polar moment of inertia. Although the latter cannot be defined purely by the waterline, it will need to be noted in the documentation and on the designers cabin specs plate for the particular hull.

There are minor forms of ballast. If a small day boat, or a speed boat, then you may not need fresh water for cooking and drinking, whereas on larger boats, fresh water tanks can be vitally important. These fresh water tanks, and also the fuel tanks can be considered as variable ballast. The variable ballast should ideally be neutral ballast, which does not upset the overall balance, but merely allow the boat to sink lower when fully loaded, or to sit higher in the water if empty, with minimal difference to the overall balance of the boat. Therefore they are ideally placed in the centre of gravity of the hull, but as this is invariably cabin or engine space, the fuel tanks are often either each side, or fore and aft, draining down into a single fuel tap off point which ensures almost perfect balance at all times. Water tanks are discussed elsewhere.

Fitting solid balance will depend upon the size and your needs. Concrete in motor boats will sit evenly across a lightweight hull and spread the load evenly, but does not flex. If using concrete to secure old pieces of iron such as broken up car crankcases, then where the iron or the edge of the cement ends sharply, the hull may fracture. If a delicate hull, the designer may wish to pour the ballast into areas lined with closed cell foam camping mats, using large thick plastic bags to prevent small leaks of concrete from actually contacting the hull, so the hull never gets any undue stress points. Few if any commercial design bother to do this, but I prefer hull reliability above all. I also add a few steel or bamboo bars in larger sections of concrete to stop it braking up if of a dubious shape.
Don't just pour concrete into the bilge. Always allow the bilge to drain cleanly and fully. Therefore add some bilge drain tubing and a couple of open drain areas to fit bilge pumps before pouring the concrete. If the boat is expected to roll heavily or take to open ocean or even be self righting, be prepared to build up some reinforcement and T flanges to hold the concrete to the hull shape and across the lower bulkheads.
The use of loose iron scrap and such like works, but is not exactly a good idea, especially if it moves in a storm and makes the boat difficult on the helm. So always pot such lumps in concrete once the ballast is about right. Bricks made with heavier items offer a good compromise during some tests, but should be fitted in discrete sections to prevent movement during test or if needing extra ballast. Sand, gravel or pebbles should be restrained in strong plastic bags if needing emergency ballast or during testing. (For ecological reasons, always try to return sea sand and pebbles to near its original position.)
In a complicated bilge, it may be preferable to fit white polystyrene foam to make channels in the bilge, then pour in the concrete, and when set, pour in some petrol to dissolve out the white foam, leaving an easily drained and ventable bilge.

Coarse gravel and pebbles can be added from a convenient beach if desperate, but will move about if unconstrained. After final tests, a little concrete can be added and mixed to keep the bricks and gravel in place. For best results, preferably wash the ballast in fresh water before applying concrete.
If the boat is likely to roll heavily or overturn, then the ballast must always be mounted securely and this means lots of strength over many decades to maintain the ballast in its defined position. This may need fitting or enclosing the ballast permanently to the hull and bulkheads such that when overturned, it will not become dislodged. Self righting boats such as the Dutch self righting enclosed lifeboats used on oil rigs, show just how safe good ballasting and hull design can be. All permanently fixed ballast must be able to allow safe draining to the bilge and for cleaning to prevent smells and disease. Being able to unbolt and lift out carefully moulded and mounted lumps of moulded ballast to clean the bilge each year is recommended.

For yachts which have separate ballasted keels mounted on bottom fins, then the design needs to be as smooth as possible, where the modern racing yachts show just how streamline they can be. Unfortunately some keel designs are also very easy to break and only suitable for open ocean work. A racing yacht with a broken or lost keel can be extremely difficult to manage and may even be worse than useless. If wanting reliability or just coastal yachting then this demands keels which are more robust in their design as mentioned earlier.

Testing boats is in many phases, the first of which is static, usually while 'fitting out'.
It is possible to test the engine while in the back garden if you can run water though the cooling system, it will allow you to fine tune and settle the engine and then shim the mountings for perfect alignment, and generally check the engine with no load. Always grease or water the stern tube to prevent the rear bearing from overheating. This in turn can power up the electrics with a fully charged battery. Disconnect the prop shaft, or ensure there is no heat build up the propeller shaft due to rotation or any misalignment. The wiring can also be fully tested.

If self righting, then alongside the harbour and use a strong crane to turn the boat over, using a nylon strop wrapped under the hull. For yachts, this means tilting the craft onto its side and watching the results.
When considered safe enough to go for a first run, and with all safety equipment checked and working, but no loose accessories, then the moorings can be slipped and open water beckons.
What also beckons is the water temperature gauge, oil temp, oil pressure, volts, and generally casting your eyes, hand and ears over any areas of concern - and being prepared to head back when prudent so to do.

Initial sea trials can be compared by following the path of a similar vessel and comparing its behaviour closely with yours. This should warn you of any misbehaviour before things get too out of control.

If a yacht then choosing or waiting for idea conditions will ensure you don't get into too much trouble. Finally, taking part in open competition or with friends in similar craft will help show up any faults or where modifications may be needed.

Testing never really ends if you want a perfect boat.

Well, there you have it.
Seven large sheets of marine plywood and a basic mast, lots of nylon dacron and terylene cloth, a home made keel and you can be sailing a two seat yacht in a few months - something to do in the garage over winter. Scale this up in steel and you can yacht around the world with a six man crew.

With seven sheets of steel or lots of steel, some chicken wire and cement, or buying a fibreglass hull, plus an nice old car diesel, a marine gearbox and some metal skills, then you can have a sensible motor boat of your dreams which is affordable.

You won't be the first to build a boat; our Bronze Age forefathers got there first.
And you won't be the last; we all work towards an incredible and exiting future.
Rocket science it ain't.
If you have brains and skills and leaving a degenerating Britain and looking for a much better life, then via the sea is as good a way as any.

Boat building and sailing can be dangerous, but cheap, fun and is highly recommended.

Bookmark the 'Magic Seaweed' website and check it before putting to sea.

Always wear a lifejacket and be properly prepared for all situations before you leave harbour.
There are no excuses at sea.

Best wishes,
J.P.

Appendix 1. Bath tubs and Hydrodynamic test tanks.

Static model tests.
If wanting to experiment with different hull designs, then the first test is to make a model of the hull and apply static tests. Ballast it in various places and with differing masses to see how it behaves or misbehaves in all conditions. Although professional test tanks are long, expensive ponds, this can also be done in any suitable water volume such as a pond or bath tub. Water is the same everywhere.

When making scale models, it is the displacement of the water at various angles of roll and pitch which matter and the relative mass and it s placement. Water does not care if its made of balsa wood, blue foam or cardboard sprayed in hair lacquer. It's the way the hull behaves which matters.

If making many comparative hulls, then it's the area under the waterline which is most important and many hulls shapes can be tested easily. For yachts, lifeboats and wave piercing designs, then much of the upper hull will also interact with the waves and this too must be carefully modelled. I find the simplest way is to buy or find a block of builders blue insulating foam, make a hot wire cutter to make five or more identical blanks, then mark and carve the short list of hull designs. Carving is done with plywood chine or rounded formers, to make a set of identical 'blank' hulls, then smoothed with silicone carbide to the final shape, often comparatively, so the five models are able to show reasonable dissimilarities for testing purposes. They are then hollowed out using a soldering iron, ballasted and tested for centre of buoyancy, marked with centre of buoyancy and centre of gravity, and given a test hull number whereupon they are then deemed ready for testing. (Or quiet pond or even the bath tub.)
I find five hulls are a good starting point. No.1 being stable with a new feature, 2 having excessive stability. 3 being my preferred initial or reference hull. 4 being unstable and 5 being unstable with a new design feature. By the end of the tests, I often have the hulls gradually reshaped to a more refined and generalised form for the intended final design. When a new idea appears from testing, then more hulls can also be made and assessed comparatively with the other models.
The range of features or areas for study will of course depend upon the designer and the needs of the hull. By having a closely related range of hull designs will highlight the range of effects and both good and bad aspects. Always remember the these are comparative, and do not guarantee the full size hull will react in the same manner. This is comparative, so whatever the hulls exhibit while under study are indicative of the way the full size hull may behave, but merely similar in the design function and not guaranteed to be identical in behaviour. Carefully learn to recognise the differences and study, then learn from the hull behaviour.

Assess the models to give a working indication of the stability, and plot a stability graph of righting moment against angle of heel. For perfect assessments, then righting moment will be a percentage of maximum righting moment between the centre of gravity and the centre of buoyancy at the differing angles of lean. The force to return the craft upright at different angles can be simply measured staticly using a protractor on the hull and a pendulum or weighted string, and a spring gauge on the gunwale for a rough working assessment of relative hull designs. Although the test does not take into account the angle of the wave relative to the hull, it does give a reasonable working curve which can be compared with other craft to look out for any dangers or to optimise the stability. This can later be compared with the actual full size craft to allow any future designs to be refined. At maximum stability, that is to say the maximum righting moment for some yachts is at a heel of about 30 degrees, when the righting force is equal to the maximum wind force on the sail, and at such angles of lean, the boat may be close to being swamped. A coaming or minor redesign will enable such a craft to maintain this maximum balancing of forces to best advantage in a race.
To assess the maximum resistance to roll (stability), then the hull can be pulled by a cord wrapped on a semicircular pulley centred on the centre of buoyancy. The other end of the cord can be attached to a mild arm acting under gravity, to show the load applied relative to the angle of the hull roll. This will indicate the highest resistance to roll, and from this the angle of the hull measured and the graph plotted, then compared with similar vessels. To restrain the hull from pulling sideways, (sway) the fore and aft waterline can have pins with simple cords to prevent sway, but otherwise free to move.

If a self righting design, then the model tests should be carefully studied and recorded for later comparison, for when the full size design is deliberately rolled alongside the harbour wall during full size tests. This can be done in a pond or a domestic bath.
If not a self righting design, then this too should be carefully recorded to see where the unstable point is reached when deliberately tipped by hand in the pool, sink or bath, to see when it will roll, its roll rate and a rough approximation of the keel placement and mass.
If the full size designs compare very closely to the ballasted model, then all is well. If comparisons do not tally, then always apply the full size data to the model for further testing. In this manner the art of modelling can become more accurate or you may have missed something. Then the model and perhaps the boat can be further modified or ballasted accordingly.
When an optimised amount of ballast is decided for the model, the hull shape and ballast can be refined by test runs of the model to see if they compare well with the full size boat, both staticly and dynamically. the refinements may perhaps be to self right in a high sea, or for stable surfing or for easy motoring or for high speed planing, but all with the bottom line of safety considerations.

The dynamic tests require longer lengths of water and this is the realm of the test tanks.
There are two main forms of testing, free and restrained, although any method is valid if it gives insight or new knowledge.
The free test will usually restrain a yacht only by the position of the centre of effective force of the sail, to allow the model to behave freely, (with just a rudder to maintain the desired tank path).
The restrained test has restricted movement usually in pitch and heave, so that the results are tightly controlled for close comparisons with similar designs. This uses strong flexible arms to limit the movement to certain directions.

Yachts can be tested with both methods where applicable and if appropriate, whereas power boats need only use the restrained, unless there is a problem with forward stability, whereupon the model should be pushed along from as close to the thrust point as possible and use a rudder or other method to maintain alignment in the tank. See later.

For speed testing, where the dynamics of the model are assessed, then the simplest option is to forgo test tanks and make a few large model radio control boats, then test these in similar, if scale water conditions. Always have the tests videoed for closer study before modifications. This is particularly applicable for a yacht, where the optimised position for the mast can be changed until the final design of hull handles really well with minimal rudder. The advantage with models is that minor changes can be applied within a few minutes, so the test situation does not change appreciably, to give good back to back assessments.
Sitting beside the boating pond on a sunny day with some blue foam and some sandpaper and five minute epoxy makes for very fast hull testing. Tailored parcel tape is perfectly adequate for simple skinning rather than expensive paintwork.
Note: Test models are not mere toys but are designed to be adaptable in as many ways as possible including mast positions, variable ballast or adjustable keel mass ands positions, and a selection of sails, or for motor boats, propeller positions and possibly a selection of minute hull modifications such as removable venting for planing craft, or different rudder positions on yachts and whatever else the designer may consider capable of offering improvements.
A model can have the design luxury of many mast and keel positions, whereas the development or final craft may only be capable of minor changes during sea trials. A model power boat can have many hull changes over an afternoon's boating (and a picnic).

Trying to assess the effects of a sail with maths or a computer is a tad difficult, whereas a model simply bypasses all the maths and theory, going direct to a fairly reliable if not perfect assessment of a design.
If designing a large yacht, then a mid-scale one man version is highly desirable rather than waste a lot of time and money in testing and modifying a large design of hull and sail.
Building a scale one-man test hull for development also helps the builder develop manufacturing and assembly techniques and always leads to a better build of the final design. Being able to take to sea in a scale craft helps quick development and that all important 'first hand feel' of how she behaves. Like aircraft, the bigger the craft, the smoother it will handle; so a small scale test jobbie will always show up problems far more easily.
(A scale model also looks good in the office or study, while a one-man scale design is great for those occasional nice evenings out on the water or local lake.)

Simple test tank design.
A test tank is a body of water with rails either side to drag a test hull through the water to see how it behaves at various speeds.
In some cases, the test hull is partially restrained and waves can be created to see how she behaves.
It is not how expensive the tank is, but how you use it. - If a specialist craft such as a power boat or an expensive yacht design, then making your own temporary test tank may well be useful.
Test tanks do not solve problems, but merely give an indication of the probable situations with the effects of modifying the design and how it is ballasted and powered. The chance to study the designs before building the real thing.

The simplest is to build with planks or breeze blocks or bricks and some plastic bin bag lining in the back garden to give a long a tank as possible. The tank must also have adequate side clearance and depth to ensure there is no reflective interference to the test runs: For a scale model about a foot long, then a three foot wide, one foot deep tank will be the minimum acceptable.
To this must be added the test track. Simply buy some steel rods which are available for a few quid and come in 22 foot lengths from your local metal merchant, plus four cheap rope pulleys about the same groove diameter as the rods, plus four nails and a suitably wide plank of wood and wheels from a kiddies perambulator.
From the cross bridge will be suspended the hull attachment point where an adaptable lever will allow the hull to move independently on the water. This is a simple arm, so a bent wire coat hanger is often quite good enough to restrain the model in the required planes and not load the hull noticeably. If a wood or blue foam model, then telephone wire nail clips can support both ends of the coat hanger.
Attachment to the scale hull will depend upon the thrust line of the power and the centre of gravity of the hull. These will be modified as tests develop and gradually refine the design.
The traveller must also be able to measure the force applied the scale hull to measure the expected power required at different speeds. If a planing hull then this may well change significantly as speed builds up, but for ordinary hulls the power will simply be a geometrically increasing curve of drag to speed. Measuring the force to draw the hull through the water need only be done with a simple spring scale. Just a lever to the drag arm to the boat, can be attached to a spring scale for weighing a few ounces. I use a rubber band and a bar of wood pivoted on a nail. The wood lever is calibrated at the far end using a pencil. The rolling trolley can be calibrated after every set of runs, by loading so the spring load is checked using simple car wheel rim weights, or a bag of sugar for models with high drag. For comparative tests, just a simple spring can be used and pencil marks made to show the relative forces needed to drag the similar hulls at the same speed.
It will be found that the drag on the boat can be easily measured using the weight of a wooden arm pivoted and pulled by the drag on the boat, but this will work in the direction of any acceleration, so must only be measured at a constant velocity, or include a link to turn the arm into a neutral plane to the direction of travel.
Speed can be measured by noting the time in seconds to do a run, but marking the rails with numbers will allow the person pushing the bridge to count off the speed in a more even manner.
It is also recommended to add a small movie camera, or digital camera with movie mode, to the traveller to record the effects for study on a computer. Nail some wood to support the camera from above, front and from the side as the tests only take a few minutes and some elastic bands is all that's needed. I use lots of blue tacky office putty. The contents of the memory card is dumped to CD for later reference. Any computer measuring should include the various test speeds and the drag so make a little chalk board to be placed in front of the camera after each run, noting the hull number, speed and force required. If wanting to make your own sensors and computer interface, see my monograph on making your own wind tunnels on this website.
Speeds do not always match the inverse square law, so try to scale the speed to the desired speed of the real hull, by working out the desired speed in 'relative hull lengths' per second and using this as a basic guide to your desired cruising and top speeds.

(Not everyone can lay out a long pond in their garden, but luckily, there is often a municipal or similar boating pond or water feature with a long concrete edge or perhaps an outdoor swimming pool in winter. If you make up a set of two upper and two side wheels to run along the edge of the pond path, or even just an angled piece of wood which can slide easily in the edge then you have a basic linear reference track. It may be a bit pitted or jerky, but essentially reasonable. To this is mounted a single arm extending above the pond to support the hull under study. This can then be slid along the pond and used to assess the drag force, and to also mount a video or camera for study.
On ponds where the water is still, but the edge is rough, then a tightly stretched line can be used. I use two large tent pegs or a nearby tree, riser blocks to keep the lines parallel to the water, onto which is fitted a long nylon cord, tensioned with a bungee, and a long nylon tubular slider which is pulled along by a second cord. I often use two tightly stretched lines and dual slider frame when I have to keep the hull at pre forced angle to the line of movement or when I needing to video close up. It is most definitely not rocket science.)

The piccie shows a test hull (in this case big enough for a real one man boat) with the hull marked to note the positions of the bow wave and size, so that optimum speeds can be assessed for minimal drag and wave formation. Note that this is a modern broad arsed ocean racer and thus has a modified semi circular hull design.

Start with a first slow run, measuring the drag on the hull at a set speed. The drag can be measured by a simple spring gauge measured in ounces or grams as described earlier.

The hull can be dragged from a point just forward of the centre of gravity to maintain a forward direction, but allow the hull to align itself in whatever condition the hull will assume.
It is probable that the designer will walk beside the traveller using a hand to push it along, although a brick on the cross traveller to keep it on the track helps make a steadier drag speed. Walking beside the traveller while pushing it and counting the seconds to run the test length, while keeping a close eye on the hull to study how it behaves.
Further runs are done at increasing speeds and a graph can be plotted of speed versus drag. This will build up a set of graphs to give a general idea of the power needed to maintain your ideal scale speed. Unfortunately the maths to calculate the actual full size power is complex and not always reliable, so it is worth the effort to make a scale model twice the size to plot a similar graph and use this to make a reasonable projective guess of the probable power needed. As the projections geometric, three models should be used, but this gets difficult.

Professional test rigs have expensive and accurate equipment. But the tests are often comparative and this applies to all test rigs no matter how meagre.

For motor boats, you can include a motor and propeller to the model, then this can be modified to refine the alignment of the thrust line and measure the power to the motor in amps at different speeds. Use a long piece of stretched string above the hull to guide it up the tank while measuring current in amps and noting the hull action. Or use a long piece of straight wire on the traveller and a U bar or two nails on the bow to allow it to be guided but not apply any other force to the boat hull. For the best, then a pivoted pair of arms to the boat can be used to only control the straight ahead alignment but allow the boat to bob up and down, and also to roll and sway side to side, but to move forward at its own best speed with no other constraint. This can be done with three bent pieces of wire coat hanger to allow it to move forwards freely under its own power. The current in amps can replace or preferably closely compare with the drag plot lines on the graphs.

Restraining the model along the line of the tank when connected to the traveller is easily done with U nails and wire coat hangers. The art of bending wire coat hangers is fairly straight forward, enabling a variety of customised arms to control or support the hull as required, to allow various tests to be run.
Arms for just heave, or to allow roll and heave, or what ever is required, can be made in a few minutes using pliers. Likewise, by using blue foam to make a selection of hulls, simple nails can be pushed into the foam at different positions to assess the behaviour, along with, of course, differing piece of lead for variable ballast.
The models must be hollow so the position of the pivot is placed in the centre of gravity (with ballast), so the hull will take up a natural position in the water and not be adversely controlled by a poorly placed mounting pivot.
If many blue foam hulls are used, then even a simple nail and piece of string makes a perfectly flexible attachment to the drag scale arm. In most cases, it is the efficiency of the hull that is important, so only comparative forces are needed, as the better hull will need less force to drag it through the water. Just a pencil mark beside the spring lever is all that is needed to see which hull offers the least drag.

With powered hulls, plot the graph of power supplied to the motor relative to the speed and if a planing hull then develop the design so the planning speed occurs at a lower power without compromising safe hull stability.
Also look out for any unwanted bow and stern wakes which could upset the readings, although in a full scale hull these may well differ, but it is best to be wary of any unusual effects of the hull design, as this is where test tanks are worth the time spent.

A couple of afternoons making a rough tank and a few careful testing sessions can give good information and indicate the final hull design and its desired subtleties to any similar hull designs. For example if you make a bad choice of hull design then you can make runs comparing other designs, to make modifications to the preferred hull. If the design looks too radical or inappropriate for your needs, then use the graphs to see just how far away from optimum the design is, and how much hull redesign may be needed to be as efficient as any more conventional designs.

A large sheet of blue foam can cost a couple of pounds and a hot wire cutter or sharp knife and silicon carbide sand paper is all that's needed to make test hulls. By cutting out blanks all the same size, then making similar hulls with slight differences, the designer has the chance to play about with these designs ad infinitum to see how they compare. The hulls can be cored out to add or adjust ballast. Simple nails can be pushed into various positions in the hulls for towing points. Blue tacky office putty can be applied to a dry hull for strakes, keel profiles or other features if needed.
Positioning the central pivot (nail) in the hull should be adjustable so that the most rearward position can be assessed so it instils instability at various speeds and can be further assessed for optimum centre of mass relative to centre of flotation at various speeds.
With a power boat, you may also wish to place the point of contact at the propeller and sea how it behaves, although without use of a rudder, this can be problematic, so use a long string and a piece of coat hanger as the hull guide. Or simply conduct a short run to see how the hull rides and behaves at various speeds. This is best done with a cheap radio control powered model with a rudder.

All this time, the tests will include adding little weights of lead, such as old car balance weights, positioning them to the various hulls to see how they behave. Don't forget to note the weights on the chalk board after each run.

A chalk board may include : -
HULL number XXXX.
SPEED. XXX seconds to length.
FORCE. XXX ozs (gms)
Centre of pull, position 1, 2, 3, 4, 5, 6, 7. (With 4 being the mid point for all hulls.)
BALLAST Front XX oz (gms) Mid XX oz (gms) rear XX oz (gms).
The video clips will show the way the hull behaves, and the pull load indicated the drag factor, from which assessments can be done of the ride position, and general handling. Where waves are includes, these can be better measured by comparison with the hull size e.g., wavelength = 1x, 2x, 3x hull length etc.

Note the best hull and how it sits in the water with the best ballasting arrangement. Compare with the others and learn more from this.
When a hull is leaning to one side, the centre of gravity as deiced partly by the ballast, will be offset tot he centre of buoyancy, of the displaced sea water. The further these are part in the vertical plane, the more effort there is to right the craft. when looking at the front of craft in the docks or harbour, decide the centre of gravity, and also the centre of buoyancy using a line angled about the painted waterline.

Once an optimum hull is decided, it can be tested again to see where the hull begins to become unstable, it can then be assessed with waves from all four quarters of the compass to see how it behaves by rotating the semi-restrined hull in the tank, and using a plank to make various types of waves and sequences of waves to the rig, by simply holding the hull in the alignment required for assessment. It is worthwhile using the model to assess waves meeting the hull from different angles, so the hull should be freely supported in the water at various angles as you make varying sides of waves, preferably in groups of waves as compound changes may lead to an unstable condition if poorly ballasted or the centre of gravity is badly positioned.

For testing yachts, then the wind force will be applied by either a model sail and a wind, or by working out where the most common position of effective force on the sail is acting in most conditions, then placing the rig link to this point. It will be part way up the mast and to the rear of the mast for a single sail and with two sails may be near the mast. For reasonable results it is better to use a wind machine, preferably done on an open model boating pond with a radio control model, as the forces applied are often far too delicate and variable for a test tank.

If making a radical ocean going yacht, then always start with a selection of scale test tank hulls, then a couple of large R/C models, then a large scale one man hull before building the real thing.

On a still pond or a tank, and if using a radio controlled rudder, then the wind pressure can be replaced by a pull thread, (a standard reel of strong cotton is perfectly good enough), acting at the centre of wind pressure, pulled at various angles to check the keel mass and running characteristics.
When pulling on a cord to simulate wind pressure, and needing constant pressure, add a small weight mid point in the cord so that the pressure applied can be easily registered by noting the amount of droop in the cord caused by the weight. Endless wind angles and pressures can then be assessed very easily, even on a still day. This can lead to hull design to cause minimal rudder control for maximum racing efficiency. With a little practice, gusts can also be modelled to assess overall stability near the more dangerous margins of the craft.

Most people never run such tests. - Only when a full size design shows constant or unusual problems is such a test tank employed to try to help study and understand the problems and perchance give insight towards solving them. I prefer to solve problems, or at least understand them, before building larger craft.

The designer can apply a similar if simpler test rig to a domestic bath for short assessments which are quite capable of delivering good data. You may wish to get the water level high enough to give the sail rig a low angle for the thrust line to the hull and to ensure a steady drag and thrust line or to video from the side. Then lower the water level to play with various wave forms.

With a working hull form, the designer can test to see how the waterflow around the hull follows, then separates towards the rear, causing eddies and greater friction in the flow. Where this can be reduced, the craft will move faster and display lower drag force. Chopped or shredded tissue paper in the water can help illustrate the situation and should be videoed for later study. Likewise stern eddies, rudder control, keel behaviour and such like.

For yachts, it is important to assess the heel force by studying the sideways force when moving forwards and where the centre of hydrodynamic force is applied, relative to the sail force. If this is unduly large then the boat will heel badly in a side wind, and make rudder force larger than needed and the handling inefficient. By testing and measuring the optimum position of the sailing force across the hull, the mast can then be positioned with greater effectiveness and efficiency. In a test tank, the position of the centre of pressure on the sail can be carefully noted by gradual adjustment of the link arm and carefully noted relative to the waterline, and then the mast and sail fitted and tested to check the whole works as expected. If all is well, little or no rudder should be needed to sail an optimum course in optimal wind at an optimum angle.
The forces applied when heeled, will move forwards slightly due to hull profiles and as the various forces all gradually resolve, and the hull shape and mast positions will need to be studied. In the real world, such situations still apply but are not so easy to study, and good handling of the craft is where the final decision is made and this often includes a small rudder force so that the craft is kept under tight control and always that little bit more responsive. Five degrees of weather helm is often considered good on most mid range craft and ensures the craft will automatically luff in a loss of control or safety situation. And vice versa, in a gust, the craft will also luff to make the most of the extra speed available.
Minor modifications can include adjusting the keel position and slight changes to the hull profile, or more often just the sail settings, or mast position. Consider at least three mast positions on any test rig and any test yachts and full size prototypes.

Once forward speed for top speed or for economical cruising, then the stability must also be checked by making a wave tank. Unfortunately a wave tank may need waves up to ten times the height of the gunwales, so that the boat can survive almost all seas. This will closely concern hull shape and the position and mass of ballasting. To make waves, then a large plywood plank is employed, but getting this to work well is very messy. Finding a wavy coastline and using the model with a video camera is probably better if living near a suitable beach or coastline. Have a tether to retrieve sunken model boats in surf and place the radio gear in plastic bags. Ponds and lakes tend to have marginal and often lame waves, whereas the seas can offer some really good testing wave forms, and with close pitches between minor waves. Making a one man scale boat or yacht is recommended for final testing if heading out to open oceans in the full size craft.

Walking out in the waves in your bathing suit on a sunny day with a large scale model yacht and a video camera tied around your headband, to see how the hull behaves at all angles to the waves, is better than laying around sun bathing. Include adjustable ballast weights and sail it under any wind in various directions to get a good half hour or more of video footage. The breakers near the shore and the cleaner waves or swell further out, can offer a range of environments for a scale hull, or selection of hulls.

Whether motor or sail, if it is an expensive design, then standing up to your chest in breakers on a beach with a six foot model is highly recommended and will always pay off the investment in hull design and initial assessments of how to refine the hull profile, handling characteristics, self righting abilities, ballasting and other refinements.
Any motor hull design will need a decent motor, so a modern scooter moped starter motor and gel battery is recommended, controlled by a solenoid relay from the donor moped. They are cheaply available from motorcycle repair shops. These motors are NOT good for long term use and should only be used for two minutes at a time for testing purposes. You will have to make your own propeller. If wanting the hull as a toy for afterwards, then fit a 30cc two stroke chain saw engine.
I occasionally build custom test hull designs in steel, plywood or compsites. On wire control they cost from 150 pounds, and radio control from 250 pounds. With chain saw engine, from 350 pounds. Yachts with sails and radio from 400 pounds. Email with details of your hull design. The models can later be remodelled to match the genuine article.

Appendix 2. Bow manoeuvring motor.

Making such motors sea proof is always difficult so try to buy a proper item if possible, otherwise make an easily replaceable item. It is difficult to find suitably powerful electric motors which are bi directional, although some starter motors are capable. As these often have long shafts, they will take a propeller much easier and the shaft allows a few rubber seals to make a reliable sealed motor casing. The motor can be glued inside a snug fitting steel tube with three welded arms or a plastic tube sleek wooden spacers to position it in the tube. Make the mounting strong, as some starter motors have a powerful kick and may need modifying to prevent torque problems. To reduce the motor kick, soften the spring pressure on the brushes or increase the air gap, otherwise fit a power resistor in the circuit or have a two stage power supply.
The motor housing will have end pieces of metal or made up with fibreglass to hold the shaft seals, and the other end also sealed with just two heavy duty wires exiting for connection. When working well, the assembly is epoxied to become waterproof. The motor is then controlled from a switch and battery using standard heavy duty relays to allow both manoeuvring directions.
As starter motors are only used for less than ten seconds or so when mooring, then they are usually rated within their acceptable limits.
To make such motors waterproof for many years is almost impossible, although using just a couple of rubber oil seals on the shaft and no other weak point, then leakage should be minimal. When the port or starboard switches supply 12 volts to the motor, they can also power a simple 12 volt car air pump which pressurises the motor housing, and with the aid of a very small bore bleed valve at the base of the motor, can purge any internal leakage.

Another cheap option is to use a dedicated small outboard motor fitted in a special cross inverted T tunnel inside the bow, such that it can be rotated for starboard and larboard directions, and use it via a couple of simple control cables, one for throttle and one for direction with a neutral mid position. Once in harbour, it can be demounted and fitted back on the dinghy. As outboards are fairly cheap, then a dedicated mini outboard can be fitted as part of the hull design. Where electric outboard motors are available for lake use and have reverse as well as forward control, then the choice is obvious and are also far less expensive to replace than commercial bow thruster units.

(An alternative to a bow manoeuvring motor is to use a 'sail drive'. This is similar to an outboard motor, but with just the lower section fitted to the hull with a folding prop. The sail drive is expensive, causes drag and are often fixed.
By using a standard outboard motor and placing it in a tube in the hull, the outboard can be lifted up, flush with the hull when not in use. With a simple blanking plug on the base of the outboard, it will make a far more efficient, flush fitting variation to the sail drive. Being in a circular tube, there is also the option of rotating the whole unit to offer superb, 360 degree manoeuvring ability. They are also cheaper to buy easier to maintain and easier to replace when worn or damaged.)

Appendix 3. Stabilisers.

Stabilisers use underwater side planes which tilt to stabilise the hull, by changing their angle so the roll of the boat is reduced. The force applied by the side planes depends upon the forward speed of the boat, the power of the planes and the speed of reaction of the control system. Such planes need not be very big, as the force of water pressure is phenomenal. Even submarines using feeble electric power have small planes. Planes about half or quarter the size of the rudder should suffice.
The planes are prone to be knocked off when mooring beside a harbour wall, so should be sprung loaded, or able to be partially broken rather than damage the control shaft. Short stubby ones often cause more drag, whereas long thin planes are more efficient but terribly delicate, - not unlike hydrofoils.

To be effective, the planes must react quickly and the response times have to be faster than most swells and common waves and as such, almost instant response is needed.
The response is controlled by either a pendulum or a gyroscope sensing the deviation from the (relative) upright position. A partially damped pendulum has better effect, as if the boat is in a tight turn, then the boat will need to lean to maintain passenger comfort. A gyroscope may be clever, but the control system is particularly difficult to make and always prone to problems, so is best left to professionals. Even a simple pendulum will react to the relative angle of the boat, and control relative stability via its signal. Large liners may be able to ignore waves and stay level with the horizon, but smaller boats should still work with the swells and larger waves to some extent. A variable resistor on the pendulum pivot can sense the difference of voltage to port or starboard can then give the signal to the stabilisers via a control circuit and powerful, fast electric motors. Alternatively, just a simple switch on each side can also switch the stabilisers, although a variable resistor with a simple op amp can give a centre neutral and send a variable signal to the control relays to power the stabiliser motors either up or down in a more subtle manner. Just one signal can move the port stabilisers up and the starboard a down, and vice versa. The pendulum will be designed so it will not act when the boat remains within the desired limits. The feedback control may be adjusted to modify the response time and the effect to enable a decent stabilised ride to be obtained, but unlike autopilots, should not be heavily damped to slow the response time, but to maintain good overall control.

To make such devices, a simple shaft with control arm is positioned in the flanks of the hull below waterline, either side of the centre of gravity, or nearby, with simple water planes bolted to the shafts. The shafts can be mechanically linked to work off a single bi directional motor in a small hull which ensures equal and opposite plane angles on each side. The inner arm is connected to a geared electric motor or hydraulic ram working off an engine powered hydraulic pump and valve control block.
In a small hull then a simple, strong tube can be mounted across the hull, with the shafts exiting with rubber seals or stuffing boxes and internal arms to work equally in opposite directions. The cross tube will also greatly improve force resolution to reduce distortion in the hull by applying the forces evenly and opposite into the sides of the hull and also ensure the control motor will act evenly on both hydroplanes.
The planes are ideally pivoted centrally across the area of deflection such that they need very little effort, allowing a nicely balanced design which is easily made for a superior quick response with minimal effort.

By sensing the engine revs or throttle position, and if the planes are suitably distant from the centre of pitch, then the planes can also be given a secondary, collective angle to enable balanced fore - aft control.
If fitting the stabilisers near the rear of a high speed hull, then they could be moved in parallel to alter the angle of ride of the hull in the water. This can be done by fitting a second control to the primary stabiliser control motor, such that the whole assembly moves up and down, while still keeping roll to a minimum, this secondary option should be controlled manually as a trimming device, from the helm or throttleman's position unless used automatically to reduce or modify pitch.

In case of failure, the stabilisers must always return to a fail safe, neutral position.

Appendix 4. Composite sails.

Always compare with similar craft and test with a basic version of the sail first, until the ideal shape is created. A sail may take three or four rebuilds before being close to ideal. Don't worry if it looks tatty, patched or even ugly, as long as the shape performs as desired. This is a tailoring exercise and many iterations may be required to attain perfection in fit, shape and overall performance.
If a small yacht, then take along a piece of bright chalk to mark the sail where it needs changing, and carry your sail makers sew bag for minor changes while on the water. This information is then used to modify the construction methods and cutting patterns and tensioning, should you get deeper into the subject.
If a larger craft, use a felt tip marker pen to make small marks where the sail needs to be modified. If a test rig prior to full build, then a permanent marker is recommended. Use a marker similar in colour to the sail, and number your changes in order.
If a radical design, then refer to the standard 'sail to waterline graphs' as starting points if the desired power is unusual compared to the standard waterline graphs.

Aramid is surprisingly cheap to buy, unlike carbon fibre (carbon-carbon.)
With the advent of microfine rip-stop kite materials, an advanced sail can be made cheaply, if somewhat more involved than sewing a standard sail.
To make your own, rather than pay hundreds or even thousands of pounds, will need a large area the size of the sail and then to make a curved former. The former will be a three dimensional shape, along the lines of an airfoil to ensure the down stream airflow over the back of the sail maximises the vacuum effect of an airfoil section. If no 'sail loft' or a large room for such a curved former, then digging up the garden to make a suitable shape can be done before turning over the soil for winter. A large plastic sheet from a DIY store can be used to cover the 'sail mound'.
The curvature of most triangular sails are very similar and it is the horizontal curvature back from the mast leading edge which is to be constant straight line up to the top. From this imperfect leading edge is to be desired an aerodynamic curve as found in many sailing and aircraft books. The same force keeps microlights, paraponts and other soft airfoils aloft. Look for NACA as a starting point. The curvature will change according to wind speed and the way the sail is rigged, so that the air separation of the downwind low pressure side is kept to a minimum for maximum force. Where the wind is cleaner near the top, the curvature can be a slightly higher speed airfoil section, but I know of few sail designs which are good enough to get this sophisticated, so a standard curve is often plenty good enough for almost all sails.
Therefore the leading edge part, nearest the mast, will have a slightly deeper curve than the trailing edge of the sails, with inserted thin fibreglass tapering stays sometimes used to help control the curve, althogh any reasonable curved shape will suffice unless racing.
(Q. Which way around would you fit the tapering stiffeners to get the ideal airflow curve across the sail ?)

The sail is made over a large sheet of polythene so it can be easily removed later. On top of the curved former is placed the first outer sheet. The air proof sail cloth is very lightweight fabric, preferably rip stop as used for kites. For long tern use, it should also be resistant to ultra-viloet light.
As this is an airfoil section, the air sheet should ideally be made from tapered sections of cloth sewn together to make up the three dimensional curve. For small sails, it is possible to stretch and tease the warp and weft into the three dimensional shape of a small lightweight layer such as the size of a wind surfer and only need two or three sheets for a one man boat. Slightly gathering some of the hems will also help create a curved profile.
The three corners are marked and spokes or poles are positioned to take metal eyelets, around which to wrap the aramid. It is possible to replace the metal eyelet with aramid and nylon bindings for light weight work, but small metal eyelets are far more abrasive resistant in heavy sailing, as aramid is not very abrasion resistant. In most cases, the eyelet will be within the triangular profile of the sail.
Always use gloves with aramid, as it is a skin irritant. (Although I have never been irritated by aramid over many years.)
The aramid strands consist of one large roll of aramid cord. When this hard to find, spend a few hours removing the tiny and often annoying binding cord which holds aramid mono aligned tape neatly. Then rewind the aramid strands into one large ball of aramid cord ready for placement on the sail area. The almost endless aramid cord is wrapped across the former and around the posts or eyelets.
The eyelets should be polished to remove any abrasive areas. Aramid is not abrasive resistant over long periods, so always protect aramid fibres at the sliders by carefully polishing their mounting holes and always apply silicone sealant after the sail has been used a few times, after it has settled and been fettled, so the aramid abrasion is greatly reduced.
The aramid strands are carefully laid over the sail area to build up a neatly spread multi way array of strands.
Secondary strands are included from the end of the boom to the numerous positions up the mast for the sliders of the mast edge or bolt rope, and always polish the slider holes to prevent undue abrasion.
By carefully knotting between each slider, the sail and bolt rope can be made even lighter rather than having to sew a larger rope to the leading edge.
The larger the sail, the greater the number of strands needed to maintain the smooth shape of the air layer. Ideally the aramid could be teased to cover the whole sail, but this is almost impossible and not worth the effort. Be it sufficient for the aramid to support the shape and take the forces generated by the sail.
Try to make the aramid fibres lie flat rather than rounded, and if possible find a suitable artists brush to allow the fibres to be bushed flat. Waterproof PVA was originally my method of keeping the fibres flat, but has not worked too well to hold the sheets together. I now prefer spray mount, with my fingers teasing the aramid into a broad, flat set of lines.
No strand should be tighter than any other, otherwise this will cause poor aerodynamics and localised stresses, so carefully lay each long strand as a smooth curve over the sail area, brushing over and over again until it is used up, then tie off the last strand beside the eyelet.
Continue until you have long strands of aramid evenly spaced across the whole surface of the sail area, with the inner cords curving neatly to fill the sail area. It is necessary to hold these strands neatly, so small dabs of silicone sealant can be used, although I prefer to use the aerosol 'spray mount' used by photographers, as it allows the fluffy strands to be lifted and repositioned as needed.
Eventually the sail area will have a hundred or more strands evenly spaced across the whole sail area, so that the intermediate gaps will not distort unduly by the airtight fabric.
The whole is now massaged so all the strands have even loading when the sail is under load.
The ends by the eyelets are now lightly wrapped to hold the cords neatly. Do not bunch the cords up, but merely hold them onto the eyelet. Use some silicone sealant and a little twine if you prefer. Same for the mast sliders.
Any thin pockets for fibreglass stiffeners are added. If the upper sail is a racing type, then more aramid should be used to support the outer edge of the uppermost stay.
The first airtight layer of nylon, dacron or terylene is now applied over the aramid. This is bonded to the aramid using the minimal dabs of silicone sealant, then lightly stitched into position if really needed. It can be later sewn through fully after the sail has been worked a few times and settled down in high winds, or if there is a suitable test rig on a windy prominence nearby to allow the sail fibres to settle. The edges are now lightly tacked in place, but need not be fully secured yet, just tack stitching. Place the sail on a test pole using just the three corners and allow a few hours at gas wind mark 6 should do nicely to settle the basic fabric. Any tailoring and any teasing or readjustments done at this stage, then back to the hard working sewing machine for a full stitching session. If no suitable wind or rig then simply support the sail off the ground by its three eyelets or mast supports, then cover in plastic sheet and gently apply plenty of sand evenly across the whole surface to represent the wind. While under working pressure, massage the fabric where it may ruck or crease, to tease out any imperfections, and when set, then remove and tailor the fabric as needed. If on a sand load, then the edges can be hand sewn to ensure the final machine sewing will be perfect.

Applying a load before final assembly is my own preferred method of sailmaking and is not known elsewhere.
I consider that primary load application will allow the sail to take up its natural shape and any adjustments made, to get a even and smooth airfoil shape. Massaging the sail prior to final sewing may make the difference between first and second place or a reliable sail with even tension, or a rippled or even a ripped sail. (The mast edge line must be straight when fitted to the boat.)

An ordinary, good quality sewing machine is possible as modern materials are so much easier to sew than the old canvas and rope items. If the sewing machine is not up to the job, then you are probably making a very large sail and this will incur something more than 'pocket money'. A good DIY sail for a two man yacht need not cost more than 40 quid, often less.

As this is an airfoil section, the air sheet of larger sails should ideally be made from tapered sections of cloth to make up the three dimensional curve as found with all types of modern sails. Because the aramid is taking the strain, the lie of the warp and weft is not so important, but always tease the fabric to get the best lay of the cloth prior to sewing the sheets together and be wary of gathering too much. I like all my joins to flow along the airflow direction for minimal drag across the sheet. If there are to be any gathered rucks, always make sure they run horizontally when the sail is used, so that the airflow is minimally disturbed. (There are techniques called turbulators on the leading edges of an airfoil to help maintain flow attachment, but these should only be added later if making a top class racing sail which suffers chronic laminar flow problems and needs testing. It should be tested using standard methods described in my wind tunnel monograph.)

For small sails without aramid, it is possible to merely stretch and tease the warp and weft into the three dimensional shape for a small lightweight layer before sewing the edges. Where the layer does not bend, then it must be tailored to suit the curvature using standard sailmaking techniques.

Preferably while still tensioned on the sand or wind rig, the edging is now added. Using tape at the trailing edges (leech) will give a cleaner airflow for minimal drag.
If there is enough room in the sliders, always polish the insides of the holes before sewing to the bolt rope.
Use a round rope for the bolt rope nearest the mast and wrap the layers neatly over the rope to give some form of curved leading edge. Beside the mast I like to have excess cloth folded back to contain tapered fillets of foam to try to reduce the leading edge drag around the mast area. The foam is to reduce the horribly inefficient dip between the mast airflow and the sail and smooth the transition area between the rope and sail cloth. Being foam, it reefs without hassle and usually lasts a year or so before compacting after winter storage. For such reasons, I prefer my sails to be stored hanging up in dark, dry areas, not unlike oil paintings in the cellars of museums. - perfectly safe and ready for another season.
Allow excess cloth at the edges so that it folds back to replace the leech tape and have better strength and smoother aerodynamics.
(To clean up the leading edge airflow, I've experimented with plastic mast clips to try to smooth and control the leading edge airflow, and may yet return to make a more updated version, but in the meantime a little foam may do no harm if racing. Where the leading edge must be as clean as possible. The leading edge of some sails can be inflated not unlike paraponts, to affect a cleaner airflow around the mast / leading edge and help reduce the amount of flow separation downwind, but I'm still developing this concept and the clippers have minor problems rotating, although are much more effective than making a partially rotating mast. See thesis C.)

I prefer thin climbing tape at the trailing edge Leech for cleaner aerodynamics as this reduces the exit airflow drag on the sail. The trailing edge tape should have a small but strong cord threaded down the tape and secured at the top, with the bottom adjustable using double buttons or a larger version of a jacket hood cord adjuster. This will allow the trailing edge to be fine tuned while at sea. I use parracord for adjustment as, should it become sewn in place in emergency repair, the inner Kermantle strands will still allow perfect adjustment. For very thin edging, then the parracord can be inserted, then the outer woven sheath drawn out to leave just the inner strong strands which can be siliconed at the bottom edge for tying purposes. If the trailing edge using tape flutters too much, then silicone sealant can be massaged into the tape at later date to increase stiffness to keep the trailing Leech edges under better control. If it still behaves imperfectly then little lead sleeves or pads can be inserted in specific positions to dampen the edge and give cleaner airflow with minimal exit flow drag.
Aramid or other synthetic tape or ribbon is an edging option but hard to curve easily where stitching can distort the tape. Only use tape if it will curve easily, otherwise it can distort too much, and always start sewing from the middle so it will have a better chance for the tape to lay flat. If using tape for curved surfaces, always clamp the middle and work towards the ends to positively distort the warp and weft into shape. With very curved edges, it's better to use a round cord, or two thin tapes or ribbons with staggerd creases as this can curve far more easily along the trailing edge than any flat tape. Tape can be used for the straight boom and mast edges if needed for specialist sails.
Parracord is a good and cost effective choice, as the inner strands are strong, whereas the outer woven sheath makes sewing easier and even allow the odd stitch to go astray without causing any real problems, and also allows the sail to take its own shape with minimal stress. The inner strands may often allow the sail to settle easier into its own shape without stressing the internal core strands. The larger version of parracord is used by mountaineers. It is available in many diameters and colours and commonly referred to as Kermantle or paracord. (As used on parachutes, from which a couple of really decent small sails can be made for under 40 quid if you are on a tight budget.)

Nylon, dacron and terylene are easy to sew. After many decades, waxed Dacron is still my favourite thread.
Investing in good needles and palm pads is highly recommended. Never force your wrist as this part of the anatomy is at risk to repetitive strain injury and you will need to take time to build up strength without injury.
If new to this process, then make up many test pieces and test to destruction, noting the deformation under load and then using this to advantage in the design process.

Unless making a tall, thin racing sail, there may be some need to use tapered fibreglass 'stays' in the sail, although pockets can be added if you wish. Make sure you inert them the correct way around, as many sailors do it incorrectly - remember the desired shape of the airfoil. Adding these stays into the sail with pockets is simple sewing, perhaps including some extra aramid from the top eyelet to the pocket to act as an internal support to hold the upper edge of the sail to greater advantage.

The whole can now be properly sewn together. The dabs of silicone sealant can be strengthened with light sewing at each junction of needed to keep the aramid strands from migrating. The edging must be strong, although only to prevent fraying, as the aramid should now be able to take all the pressure from the sail. The sail cloth can be lightly attached with small dabs of sealant and all the high tension end points gathered neatly and sewn together.
Unlike traditional sails where the air pressure passes through the sail cloth to the fittings, the aramid sail takes each individual part of the pressure and applies it down to the eyelets and sliders for even force throughout the sail to maintain its shape. This also prevents a big rip from happening so easily and can be far lighter or stronger than many other large sails.
The air proof layer need not be perfectly truly airtight, as minor bleed leakage will rarely be noticed, even on a test rig. For this reason, lightweight rip-stop kite materials is excellent for many smaller sails, especially if expecting close boom work from other competitors.

The leading edge of smaller sails can be sleeved to slide over a free standing mast such as wind surfers and can give a very nice airflow.
(See also wind tunnels monograph on this website which desribes how to measure and assess airflow over various surfaces without expense or need of a wind tunnel, which a working sail rarely needs anyway. The various techniques can be applied to sail while at sea and can give clear studious of where the air is working and where it is stalled or delaminated. This may help study the airflow over the sail and perchance see where any inefficiencies occur and how to ameliorate or eliminate them for maximum sail power with minimal weight. There are many cheap yet effective methods with which to assess a sail in working conditions, many being highly applicable to sail design.)

As waterproofing the air layers is going to add extra weight, it is best to allow the cloth to breathe. If sewn properly, the sail can also be carefully folded for storage without undue hassle. Although it will never furl or pack away tightly like a standard, single cloth sail, but should be neatly folded in a multiple Z pattern so the internal structure is not disturbed. If rolling about a boom, always do it very lightly for winter storage purposes.

If making various sails, then it is worth while making a polar diagram for each sail (and keel setting) in each condition for later comparison. After making a few sails for your rig, there is the ability to chose the best sail for the day and be ahead of the rest. The polar diagram is just a series of concentric circles, with the direction of wind direction coming from the top, and each ring representing progressively higher true yacht speed relative to each angle to the wind. A steady sail state of about 15 minutes should give reasonable working data to make each plot.

Tip: Always add a few tell tales to your sails. These are pieces of bright or contrasting ribbon or yarn, which show how the wind is flowing over the sail, and off the edges. These are the only real way to tell when all is about as perfect as can be, for both test rigs and daily use.

Tip: When checking the wind or making graphs, use a decent anemometer. Here are two popular models of my friends, and one of these displays the truth. The better one naturally works at the optimum direction to the wind at all times and does not suffer from a poorly held position. It has a cap, but this is a minor annoyance for decent data. Simply keep the cap on a tether. The other, stylish item may look clever but is what I consider a lesser piece of kit, suitable only for 'boaties'.
Always choose quality rather than fancy, expensive tat.

Appendix 5. Propellers and shafts.

Here is a piccie of the latest forward facing, dual, contra rotating propeller. It is not a common form of propeller and many may have doubts about this level of technology for the involvement used and many believe it's too much technology. The advantages may be greater manoeuvrability nearer the centre of rotation of the hull and less prop wash, but at a massive cost in complexity and attendant chances of failure. Probably only suitable for 'lardy liners' needing manoeuvring rather than ocean performance, and high speed racers. For normal use, such technology may well be completely unsuitable.
At the other end of the scale, human powered hydrofoils use large diameter, thin carbon petal propellers which look very similar to large model aircraft propellers.

There are also feathering propellers for yachts, where the propeller offers very little drag, and when powered, will open up and take up the power into the hull, otherwise they remain with the blades folded back. Designed well, with a shrouded boss, a freewheeling prop should offer almost no drag. It is also possible to use freewheeling propellers, but these are rare.

Most props are magngnese bronze or aluminium bronze, although anodised aluminium allowys, stainless steel and plastics can also be found.
If a bronze propeller and a steel shaft, then always add a zinc collar to reduce galvanic corrosion.

It is important to make a good working guess as to the size, pitch and type of propeller for your hull, engine power and rev range. This demands research of similar hulls and engines to get a close working specification.

Making a test propeller is possible if you are unsure about the size and pitch of the propeller for the boat, whereupon a steel propeller can be made and adjusted in pitch or reduced in blade area or diameter until it works perfectly or close to the needs, and perhaps another made more close to the optimum propeller. Then a near match bronze propeller bought for longevity. The steel one can be used as backup and if costs permit, to cast a custom prop or for further development as needed.
IK Brunels first large propeller on the SS Gt Britain, was close to modern day propeller efficiency, so don't be too afraid to experiment.
Being able to moor close to shore and drop overboard with a lever to tweak the propeller pitch of a test rig steel bladed propeller is priceless on sea trials, as only variable pitch propellers have the luxury of optimising the pitch.

To make your own temporary steel propeller, make up a steel boss to fit the prop shaft, then choose the nearest oversize propeller as a guide and make a set of identical blades. Choose some suitably thick steel and cut two three or more blade blanks, then clamp them together and grind to shape. These should be professionally welded to the boss at the root pitch angle. Then weld the roots at the desired (coarse angle) pitch then bend the outer blades carefully and evenly to get the same (finer angle) pitch at the tips. The blades can now be smoothed with an angle grinder using a rough polishing disc and refined as needed, with the welds covered with epoxy and filler to make a smooth blending shape. If a cruise boat, then the pitch can be adjusted until it runs a measured length with best time and standard revs.
If a racing boat, then both diameter and pitch are modified until it can reach maximum speed. Then the pitch can be refined to optimise the power to speed.

The profile of the blades can also be carefully shaped to maximise thrust or reduce cavitation.
If making or modifying a set of very serious racing propellers, then consider fitting an underwater camera to study how they behave at high speed as part of sea trials. This will show where the flow breaks up and the cavitation problems, to allow the design to be modified until it shows few if any inefficiencies. If you don't want to do the theory, then make up three slightly different diameter propellers and compare them by jumping overboard in shallows to change them for comparative test runs during the day, plus a vice and tools onboard for minor adjustments. If changing props in deep water, always tie the tools and the props to the hull before working to prevent loss or use a wide rimmed ballasted cotton basket hooked over the prop shaft and dangling under the prop to catch the nuts and any keys or shear pins.
(Tying heavy tools to your wrists can lead to drowning.)
A measured mile or other relative set course should be run in both directions and the engine revs and throttle setting noted and the average taken for both runs. A good log is recommended or run close to two sets of buoys or shore markers to get good accuracy of distance and pace. Many runs are done at differing speeds to work out the best efficiency of the engine and final choice of propeller.

Aluminium props should always remain anodised. (See home anodising on my website.)

Standard propellers are fairly broad pettaled shapes, whereas high speed propellers have a more streamlined shape to reduce cavitation and vapour from excessive suction forming on the leading (back) face. There is a vast range of propeller styles to suit all types of craft, so commencing with an optimum form or best guess is just the starting point, although in many cases, the best guess is usually very close indeed for most purposes.
Nuclear submarine propellers look like high speed versions but are actually designed to ensure silent thrust with zero cavitation, which can otherwise give away their position.

For yachts, a special type of propeller is available for ensuring minimal water resistance when not in use. The folding propeller is mainly used for manoeuvring and not for extended use or high power. The example shown is a fine example of engineering and can be fairly easily made at home with basic engineering tools. The blades are lightly sprung for best efficiency, or slightly snug fit so they fold back under water pressure and remain folded until the applied rotating power opens them up again. Alternative designs include the Max-prop and Autoprop designs.

All propellers must be balanced to ensure they do not vibrate, and preferably balanced in thrust pattern too, with all blades identical. When making the propeller, a dummy prop shaft or a set of cones on a shaft can be used to ensure the blades are perfectly pitched and run true with perfect balance and identical pitch.
After optimising the steel blade, the final runs must be made after the propeller is refined so all the blades are identical. Then the final version of the steel propeller can be used by your local foundry to cast a custom bronze propeller and the steel one protected with tar and cloth, then stored onboard for an emergency. Details of pitch and diameter should be added to the boat specs plate for the hull, along with the horsepower and revs.
Never allow a steel propeller to remain on a steel shaft for more than a few weeks, even if it was heavily greased when fitted.

The driving face of a propeller is that facing the rear of the craft.
The face of the blade facing forwards is known as the back of the blade.
Because of the density of water, some force is created as a reaction of the blade pushing against the water as if through butter, but because this is a fluid medium, there is also the venturi effect causing a low pressure zone ahead of the blade into which the propeller is pulled. Therefore the curvature of the blade is carefully matched to the optimum water speed and power applied. For general purposes, the driving face (to the rear of the boat) is normally flat, while the rear of the propeller blade (facing the front of the boat) is normally curved. Unlike aircraft, the curvature is quite simple, although the leading edge is slightly thicker and rounder than the knife-like trailing edge, so there is minimal cavitation at the trailing edge. A propeller which produces a helical line of water vapour bubbles is inefficient.
Some propeller blades are also raked backwards, and with a careful eye, some blades may be seem to be increasing in pitch as they near the outer edge.
Look and study the differences of props on similar boats in dry storage and compare with the expected engine power, prop revs and hull speeds.
The tow rope power needed to drag the hull at a set speed is the perfect power for a boat. Very few propellers are better than 75 percent efficient, so the power needed is therefore larger. It is possible to measure the tow rope power using another boat and measure the strain in the tow rope, at a set speed, but this is rarely done and only to measure overall efficiency of a particular boat or hull design. Other tow rope methods are mentioned earlier, as is a nomograph.
If you have a reference design and know the tow rope power, this can be fed back into different boat models from test tank data for comparisons with any new designs of hull, should you need it.
Even test tanks can only give a reasonably comparative set of readings and the final test is always at full scale during sea trials.

The graphs opposite are for rough guidance only, as final decisions must always be done at sea.

A very rough calculation for a propeller pitch: Supposing the designer wanted a cruising water speed of 20 knots, which is 34 feet per second. Assuming slip of 20 percent, then the propeller would need to be designed to travel at 20 percent more than 20 knots to overcome slip. Thus the working pitch would be perhaps require something in the region of 24 knots or 40 feet per second. If the propeller turned 60 revs per minute, or once a second, then it would need a pitch of 40 feet. If the propeller turns at 240 revs per minute or four times a second, then the propeller will need a pitch of 10 feet. This is a very steep pitch for a small propeller and anything over 45 degrees root angle should be try to be avoided. Therefore a small propeller may well need a shallower pitch from 10 feet to about 4 feet and the revs increased to 11/4 x 240 = 660 rpm or something in between. At 1200 rpm a pitch of 2.5 feet or 3,000 rpm and 1.25 ft pitch is better for a small motorboat with reasonable efficiency. Above three thousand revolutions per minute may be getting near a racing propeller and the design of the blades may have to change to maintain efficiency. Motor boats may often have a direct drive to the propeller, matched to the working revs of an ordinary internal combustion engine.
As most marinised car diesel engines work in the region of 2,000 to 6,000 rpm, then this is often a good working partnership for the common propeller. Small marine diesels often work up to 6,000 rpm and may include a reduction gearbox. Car petrol engines can rev much higher but for long term reliability, then engine should be running around the middle of the rev range not too high, not too slow - same as the Three Bears porridge. The lower revs are used for average boat cruising, and only speed boats may be specifically designed to become efficient at the higher revs.
Pitch calculation does not include the size of the propeller, which must be matched to the engine power and assume a propeller efficiency of about 70 percent.

The size of the propeller will need to be chosen both in diameter and effective cross section of each blade and the number of blades. The pitch only gives a generalised forward speed and does not include the amount of power applied. Power is done by the size of the propeller. This can be a thin twin bladed racing screw or a three or more bladed, petal-like traditional propeller.

Contemporary texts on the subject of how many blades should be used are generally vague, or say there is no defined number. As a personal view point, I consider such vagueness as unacceptable in any book. This of course, leaves the designer in a quandary. Although a set two blade prop will technically do the same job as a three blade prop if the pitch and diameter are the same, ift is the speed and balde profile which is also important. It is quite obvious that a basic three bladed design with average shaped blades would be more efficient for general use.
For racing, a long, wide racing blade would normally involve two blades because they are wider with long tapering ends, where the water flow rate due to pitch, will need reasonable separation between each blade as it passes through the water, so that minimal turbulence from the preceding blade does not cause problems.
For a traditional prop of the same pitch and diameter, then a three bladed may well be better, as it often turns slower and has a steadier or cleaner trailing edge vortex, so the preceding blade leaves less wake for clearer water in which the following blade can do its work. Therefore I prefer to choose the number of blades depending upon the style and width of the blade and thus, how it has the best chance to act in comparatively clean water as it moves forwards.
A coarse pitch racing blade may only be able to use two, scimitar styled blades working hard in fiercely deformed water, (not dissimilar to the hectic flows of a food blender) where only two baldes can ensure some decent water is available to apply its power. Whereas an old lake steamer may well prefer a traditional, four petalled design of propeller in smooth flowing water as it chuggs through the lake, where the water is mostly undisturbed.
Next time you look at propellers in the boat yard, consider if the blade is high speed and if so, how the water flow is controlled to enable the following blade to enter comparatively clean water in which to work.

(Nuclear submarine props are an unusual example, where they are designed to disturb the water as little as possible, and turn moderately slowly for the power they apply. The seven or nine blades may look like racing designs with their log, scimitar style blades, but are designed for steady use with minimal water disturbance in a very stealthy mode. Nuke subs won't deafen sea creatures one hundredth that of any screaming, small power boat prop. It's probably the power boats pratting about in the Thames estuary that cause some whales to get lost.)

The pressure applied by the blade will depend upon the speed and shape, and pitch, but the cross sectional area and the pressure applied will give a close approximation to the power and vice versa but should be less than 12 lbs per square inch. On smaller, high speed blades, cavitation may occur later or with minimal effect.
A small propeller will over-rev the engine, while a large propeller will have too little power to reach the desired working speed although may get close, but the engine may well be working too hard. Always try to buy a slightly larger propeller, then after tests, grind it down until it is optimised to the engine. If the propeller modifications are too drastic, then buy a more suitable, smaller prop and modify this if needed.
The size of the propeller will also depend upon the revs, where slower props may be larger, whereas a racing prop will usually be smaller in diameter, so be careful and check the areas of the outer blades and relate this the horsepower and revs expected of the engine.
When the working pressure on the blade exceeds about 12 lbs per square inch, or 0.8 kg / cm then cavitation is likely to begin and should be avoided if possible but is not uncommon.

For one-man HPV hydrofoils, start with a model aircraft propellers, mounted the correct way around, and about 16 inch diameter with a 16 inch pitch. Gearing is about 45T on the pedal crank, with 10T on the propeller shaft. I use a carbon propeller, as the axial forces under water are far higher than that used in air, although the cheaper nylon props are acceptable for testing purposes until a perfect diameter and pitch for your personal sustained power output is decided.

Propellers which project below the keel line are rare and should be avoided to prevent damage. Twin props on a deep V hull may be damaged if beached. Props can be protected by an extended keel line or fluke or an under bracket should the boat be beached regularly.
To maximise the manoeuvring in harbour, a rudder is normally positioned right behind the propeller. If two props, then consider engines which rotate symmetrically, and use two rudders for slow speed manoeuvring (or consider a bow thruster).
Always keep the hull in good condition, smooth and free of barnacles and such like.

For engines to work, a propeller is the most popular means of transferring power between water and hull.
When working at their normal cruising speed, propellers will always want to move water faster than the speed of the hull and the differences known as Slip.
Slip is calculated as the speed of the ship x rpm of the propeller x the pitch of the propeller, all divided by the rpm x pitch of the prop. (The difference between ideal prop speed and actual speed of the ship.)
Slip is usually in the region of 10 to 20 percent. Therefore the ideal speed of the boat should need a propeller twenty percent coarser pitch for the desired speed.
Another consideration is Wake Factor, where the propeller may not get a clean approach to the water. If the prop is behind a wide stern post, then the wake factor may be as high as 30 percent, whereas a forward facing prop will have zero wake factor. The wake factor is subtracted from the efficiency of the propeller power available from the core design to reduce the expected water speed of the hull by the percentage of wake factor. After the wake factor is decided, then the is will affect the choice of propeller after the wake factor has been added to the original (clean) hull speed.
Therefore on conventional designs, sculpting the areas where the water flows towards the propeller, such as a wide stern post, should be modified for optimum flow without compromising hull strength. 42 degree inclusive angle is considered optimum to get the best fluid dynamic flow.

Contrary to initial expectations, diameter of a propeller is normally large for a slow boat, where the revs are sluggish. A smaller diameter for high speed craft where the revs are in thousands of rpm.
The propeller centreline should be immersed to at least the same depth as the prop radius, preferably a little more.
Although variable pitch propellers are often used on larger boats and ships, most smaller boats use fixed, one piece propellers and thus they are a compromise, where the propeller is chosen for greatest efficiency at cruising speed or top speed, depending upon the owners choice of use. I recommend best cruising, so you will more likely get back to port at a steady and reliable pace with what fuel you have left if problems occur or the weather turns bad or the tides are against you.

The propeller is never perfectly efficient and this will differ at all speeds. An inefficiency allowance must be assessed from the difference in drag from the tow rope horsepower to that needed by an engine and propeller to drive the boat at the desired optimum speed. The builder may simply wish the propeller to work happily with the chosen design and this is also a very good choice rather than aim for maximum speed. Getting maximum fuel efficient cruising is usually a far better solution for many happy days afloat.
To check the tow rope drag of the actual boat, simply get towed by another, using a rope attached to a tension gauge. - A body builders chest expander item may be suitable, if they still exist. The easiest method is to tow the boat to shore on a slack tide using friends, a very long rope and a suitable spring gauge. If no suitable spring gauge, then use a smaller one and use a lever to double or quadruple the springs effect, nailing the lever and spring gauge to the deck and rigged to run freely through the bow. Always include the tow rope drag and speeds (of a clean hull) on the makers plate, should a different engine or drive system be needed.

Prop test.
It may happen that a propeller is not quite right for the purpose and there is a standard sequence to check for suitability.
Check the horsepower of the engine, if unavailable then guess the original pristine makers horsepower and subtract any drag from alternators, gearbox, age or condition and ancillaries.
Clean the hull and prop and rudder etc of surface drag by using a broom and a dinghy. (Be prepared to catch or net some mullet if really quiet and lucky).
Double check the diameter and pitch of the propeller first hand. Do not assume the markings are correct. This is happening more often as third party and cheaper propellers are entering the market place.
Run a test across a mile of smooth deep water. Do the run in both directions to get mean speed. Then subtract the wake factor and the actual speed past the propeller rather than the hull speed. Now compare this data on standard graphs for pitch and another graph for diameter. These are commonly available for different craft at set speeds.
Now compare these with the actual shaft horsepower at the propeller, (after the gearbox). The readings should match reasonably well, or will highlight any need to change the propeller.

A stern access or swimming ladder is often priceless during sea trials of motor boats. Make sure the engine is off when swimming, so the prop does no harm.

Propellers are not easy to remove due to the taper shaft. To remove, hope it has an internal thread and you have the correct puller. If not then an external puller is be needed, consisting of two or three arms depending upon the number of blades on the prop, such that the arms clamp the forward edge of the prop boss and the central threaded puller pulls strongly into the countersink in the centre of the shaft. Never try to hammer off a propeller as this can damage the shaft, its bearing and the prop. During removal, be careful not to lose the key which prevents the prop turning on the shaft. Most props can be removed with two or three legged pullers. If having problems removing larger props, consider hiring a Pilgrim nut.

Basic Repair.
When damaged, the blade may well be bent or mangled, but if reasonable, can be 'straightened' or re-pitched.
The first step is to remove the propeller from the shaft if possible, or if a running repair on the shore, then to do what is possible until reaching home port.
The blade should be heated, so any reshaping does not cause any more fractures in the metal. A large, gentle oxy acetylene or oxy propane torch can be used. If the propeller is easily removed, then a beach fire can be used to carefully heat the damaged blade.
Put some soap on the blade and when it turns black, the heat is getting close to reworking temperature of an alloy brass propeller. (When the soap begins to turn brown, this is the highest temperature for aluminium.) Gently hammer the blade into shape.
Warning: Make sure there is an equally heavy block behind the blade, so as not to damage the shaft if working with the propeller in place on the shaft. Two large smooth rocks are perfectly acceptable. Wear goves.
The blade is reheated constantly to ensure it's gently reshaped. When close to perfection as compared to the other blades, it's then smoothed with a file or sandpaper to make a reasonable working propeller.
If you have repaired the propeller and wish to check the balance, then it's ideally mounted between two cones on a shaft, then balanced on two horizontal knife edges such as two steel rulers edge-on, set in saw slots in block of wood, mounted on identical bricks or seats. Make sure both the knife edges are perfectly horizontally. The blade is then checked by gentle rotation for the heaviest blade which is then reduced in thickness or reduced in outer profile to match the other blades until the propeller balances perfectly with no heavy side. Always double check by moving the blade around the cones to ensure there is no fault in the cones or shaft.
While the propeller is off, it's worth turning the shaft and checking for perfect alignment, especially after clobbering the propeller which may also have bent the shaft. If the shaft is bent, then use a block of wood to protect the shaft, and note where the bend is, then hammer to bend it back into alignment. If you can use a scaffold bar to gently straighten it, then do so.
Look and feel for, and expect undue wear in the stern bearing. Order any spares for arrival at home port. Adjust or repack the stern gland as simple insurance.

If the propeller blade is broken off, then the engine must be run at reduced speed to prevent vibration and stern bearing wear. If truly desperate, then the opposite blade of a four bladed propeller can also be removed to match the broken blade, allowing half the power to be used for indefinite use. If a three bladed propeller with a broken blade, try to bolt a counterweight or a rough temporary blade in position to get to the nearest port, or sail only when the tides are favourable on part throttle.
Variable pitch propellers and anti cavitation systems should be left to professional marine engineers. I have repaired props 15 ft diameter and the reader should steer clear. The potential problems are endless and need a really good apprenticeship.

Aluminium props should always remain anodised.

Pitching a propeller.
This is given purely for reference as I suspect few if any folk do this unless in the ship repair industry.
A propeller has a pitch, that is to say, for one turn of the shaft, the blade will want to pull through a set distance.
For example, a seven inch pitch propeller will ideally turn through seven inches of water for each turn.
As the propeller blade at the tip is further from the shaft, then the angle needed for this distance is shallow, while the pitch near the shaft is much coarser. The blade is therefore twisted when seen looking from the tip to the root and should look identical for each blade.
Place the prop on a table such that its axis is vertical. Fit an accurately central shaft through the propeller boss. In a small craft, a propeller shaft will do nicely. Mark off 10 degree lines radially out from the centre to make straight lines outwards across the baldes.
Fit a horizontal reference arm or sheet, which turns on the central shaft, such that the arm remains at the same height and can turn. A long, narrow piece of plywood with a snug hole about the shaft, which remains level with the top flat face will do perfectly.
Start at the rear of one propeller and line up the arm with one of the lines drawn. Measure the height from the line on the inner face propeller to the plywood. Note this measurement. Do the same half way out of the prop and also near the tip. Note the measurements.
Move the reference arm or plywood to the next 10 degree line and measure the three points again. Do the same for the next 10 degree lines until near the upper edge of the prop.
To measure the pitch, the differences in the lines are calculated, so the height difference for every 10 degree of turn should work out to be the same across the face of the propeller. This distance is now multiplied by 36, to give the pitch in 360 degree turn and gives the pitch of the propeller.
Problems may arise if a small prop has a distinct curve across the face, so this is best checked using the aft face of the prop, which is far flatter to give a better reading.
If the blades of the propeller are all giving the same readings, (same rise in height per 10 degrees) then all is well and no real damage has occurred. Also check the trailing edges, the leading edges and tip heights so they are all the same. If one blade shows significantly different readings, then it can be repaired. If a prop shows a great difference in pitch then it may be able to be repaired and used for cruising or thrown away if very close inspection shows signs of fatigue or fracture.
A quick check is to check that the tip height of each blade are all the same, indicating no damage.

Any badly damaged blade should now be inspected for any damage caused by distortion.
After a very gentle clean with a soft scouring pad, the whole of the prop is closely inspected for fractures. If none are found, then the blade is carefully cleaned with alcohol and dried. The blade can now be checked for fractures using specialist equipment. I use simple inks and alcohol which allow a contrasting colour to soak into any unseen fractures. Some methylated spirits and a bottle of blue inkjet refill ink is ideal. Allow the dye to soak in by dousing with a paint brush. Dry it off lightly with a cloth then immediately rub over with white kiddies chalk or talcum powder. Any fractures should soak out, into the chalk after a while, to indicate any problem areas. Any fractures will either demand the blade is returned for scrap or any minor fractures ground out fully and new materials welded in place after careful preheating. Replacement is recommended as welding props is only a temporary measure. They should be cast as one piece for true reliability.

To re-align a blade, it is simply heated and hammered back into shape. The prop need not be secured in a vice, but the blade positioned on a strong bench, with the offending blade hanging over the edge, with the area to be repositioned facing downwards. The prop is tied securely to prevent it falling off.
The blade is heated with propane or whatever is available, until a mark made using ordinary soap turns dark. The blade is can now be hammered from whichever side is inaccurate and another hammer used to support the revere face of the blade so the hammer strike works effectively. Use flat, smooth hammers and take your time to make every strike count, steady, hard hits which will not damage the blade. If a small prop, then use small hammers. (I have been part of teams of four with sledge hammers on some rather large propellers and pitched using some very expensive equipment.)
When the blade is very close, it can be measured again and then repeated until very close. Do not expect to get a perfect pitch unless making a racing prop. Very close will do.
All blades should now be inspected for any damage caused by the hammering. - Use the ink and chalk again, especially near the root.
Done properly, with a good support hammer underneath, the blade should not only be the correct pitch but the distance at each mark should be the same across the face of all the blades. Re-aliging a blade can take many hours, even on a moderately small prop.

Do not clean the internal taper, merely remove dirt with a scouring pad. To ensure a perfect fit on the prop shaft, the keyway is removed form the shaft and a little fine grinding paste is applied, then the two are rotated lightly together, cleaned then inspected. If the matt finish of the abrasive area is more than 75 percent then all is well. If not, then continue light grinding until the fit is acceptable; Note: The narrow end of the shaft taper may cause a shoulder in the prop taper and this must be removed with a small grinder. Always make sure the key is slightly undersize in height, so the propeller sits fully on the taper and not partially on the key. The key is merely a torque and alignment device.

Balancing the prop. If the shaft is available for use then the shaft can mount prop and lie across a set of parallel and horizontal knife edges. For general use, a pair of spirit levels on a bench will suffice, but always do a visual check to ensure the levels are perfectly parallel, the bubbles are rarely accurate enough.
As the prop is heavy, then the shaft may not be able to counterbalance, so a free circular weight can be loosely slid over the other end of the shaft so it can roll freely. The prop is gently rotated and allowed to settle in the same spot each time, denoting the heaviest blade. This is then lightened using an angle grinder to remove metal across the blade, or where the lowest point of the blade came to rest. If the blade is particularity badly balanced, then take cardboard profiles of the blades with reference to the central hole, then use this to mark out any differences in the blades. Ensure they are always evenly spaced first ! Draw a circle across the widest part of the blades using the central spindle as the guide, then use a pair of compasses to measure the leading and trailing edges on this circle. For the best profiles a cardboard profile should be used, but any minor differences will not be noticed in use.
For larger blades, mount on cones which are secured on a test shaft, and then placed across paralell, heavy steel knife edges.

Once pitched, balanced, closely inspected and cleaned, the prop is deemed suitable for use. It may then be polished using an angle grinder and a smooth abrasive disc. Do not remove any metal, but simply aim to get a smooth surface. Any coarse pitting will have to remain - (budget for a new zinc anode). Draw the sander across the blade to mimic water flow. When the flanks are shiny and smooth, the edges can be smoothed with similar abrasive paper to ensure the edges are also smooth. The leading edge should be nicely rounded, and the trailing edge a narrow blade, but not sharp. The trailing edge can be dangerous when running astern and should be lightly rounded to ensure running astern is efficient. A sharp trailing edge will fracture and erode easily, so a smooth curve is required. (If you look at the prop of a nuclear sub, the trailing edge is not sharp, but heavily curved scimitar shape to reduce the trailing edge vortices and is an art in its own right.)
If not to be used immediately then the blade can be stored under a tarpaulin with a dollop of tar or heavy grease applied to the internal taper and any threads plus any concentric boss or nut shroud. Check the keys and keyway are in good condition and make a new key if needed. Clean all threads and inspect for damage, replace all imperfect securing nuts or tab washers.

Propeller shafts.
The propeller must have at least half a prop diameter of clear water above it, so this is the starting point for positioning the prop relative to the hull, then the sump clearance of the engine, and between these will ideally lie a straight line for the propeller shaft alignment.
The overall balance of a powerboat will dictate the engine position and this in turn will dictate the positions of bulkheads and fire walls. This then dictates the positions of exhaust routing and fuel tanks far from the exhaust, and positioning of inter coolers which in turn dictates the sea water inlet. It may be noticed on some fast hulls that the bow wave may cause a lower pressure area along some parts of the hull and reduce sea water inlet flow, this, especially at high speed, can cause overheating. It is rare, but if poorly designed, can lead to problems.
There are a few layouts for fixed propeller shafts relative to the engine, including the straight line and the V drive, coming back on itself under a stern mounted engine.

The propeller shaft will be a specific length to align with the engine position.
On larger motor boats, the thrust bearing is a dedicated item called a Plummer block.
The propeller shaft will depend upon the power output. If a powerful boat, then the propeller thrust must be passed into the hull via special thrust bearings and these must be protected from sea water and carefully lubricated. Therefore the thrust bearings are mounted near the engine. (Unless an extremely powerful engine, when they are mounted nearer the propeller to prevent a lightweight prop shaft from bending.)
If designed well, then a propeller shaft can be plain shaft, symmetrical at both ends, so that it can be turned to get double the life from a single shaft, for another decade or so from the main bearing areas of the bare metal shaft as they wear at one end. Therefore such bearings should be carefully designed and the unused bearing area carefully protected until needed, along with a replacement stern tube bearing.
Where a shaft is poorly supported, it can vibrate (often called whipping) so the shaft should ideally be supported with no unsupported length greater than 30 shaft diameters.
Note: Bearings of steel shafts are of softer metal. The softer bearing metal will gradually absorb the microscopic flakes worn off the steel shaft as it beds in or micro welds, and thereby prevent undue wear, by allowing the steel micro particles to be safely away from constant abrasion, as the rest of the soft bearing metal supports the better parts of the shaft bearing area. For this reason, car main bearings are soft tin alloys and supported by high oil pressure, whereas stern bearings of boats which do not support any real load, can even be of nylon or hard rubber and lubricated by a small leakage of sea water.

The propeller tube is often merely a thrust, alignment and sealing tube. Where the tube is moulded into a GRP or ferrocement hull, then the surface should be shot blasted to make a secure adhesion, and internally zinc dipped or aluminium sprayed if made of steel. Flanges are added to transfer the forward force into the hull. Any extending tube is coated with GRP to protect it. All exposed areas of the tube will need to be painted or otherwise protected from the sea. The bearing near the propeller will either be a set of needle rollers for a racing boat, or a bronze bush for moderate use or a nylon bush for gentle, intermittent use. If using a steel prop shaft, then the shaft bearing surface touching the bronze bush should be highly polished bare metal and ideally a grease nipple, or sleeved with a stainless bearing surface, although nickel plating and polishing may also suffice for long term, low or zero maintenance use. Because the bearing is below water level, a drip feed oilier will be useless, as oil is lighter than water, so a pressure greaser would be required.
To protect the shaft, the water seal is ideally positioned just behind the propeller and consists of a stuffing box. A stuffing box is merely a space around the shaft which can be packed with greased cotton rope to make a water proof seal which can be compressed to a snug fit around the shaft by a threaded boss or studded flange. As the seal leaks more with time, the stuffing box is simply tightened enough to reduce leakage without constraining shaft rotation.
To make your own stuffing box filling, choose a cotton or fine hemp rope about the same size as the gap, then boil it in tallow or similar water proof grease. When cool, hammer it gently into a rectangular section. This can then be tapered at the end of the rope and a few turns wrapped into stuffing box and compressed to make the desired seal. The stuffing box must have a bronze compression collar around the shaft as a steel one will surely rust and fail to work. The stuffing box collar, if a precision fit over the shaft can also double as the rear bearing if it is securely prevented from turning and not apply undue pressure on the drive coupling between shaft and gearbox.
A stuffing box can be refilled even in shallow water, as it only takes five to ten minutes to refit the packing and any bilge pump worth its salt should cope. The hardest parts of the process are removing the rusted nuts or bolts and using a long screw puller to remove the old packing. Always repack if the hull is out for maintenance.

The stuffing box packing should be finally tightened with the propeller turning by hand under water, so that just a drop of water passes into the hull every minute or so. If no water passes, then the packing is too tight, and the bearing it will not be lubricated by sea water, it will then overheat on the shaft and fail far too soon. New packing should be checked for a year and adjusted until it settles down.
Many professionals tend to over tighten stuffing boxes.
If in doubt, then for a day boat, over tighten until the shaft is stiff to turn by hand, as this helps consolidate and compress the packing, then slacken off until the shaft turns easily by hand, then just an extra mild tightening so the shaft turns happily with about one drip per minute into the bilge. It also prevents an otherwise perfect bilge to work its pump regularly, to prevent failure through lack of use, if no rain water can enter the hull.
For fancy or highly engineered boats, then a full seal is possible, with a greaser or grease nipple attached, so that no sea water enters the hull. A greaser is a screw cap with a large grease capacity, so that it need only be turned quarter of a turn once a month or more often if used regularly. Greasers also save having to find the grease gun, so there is much greater chance of regular maintenance.

To protect the propeller shaft, you may wish to apply some grease or aerosol foam grease to a steel shaft to prevent rusting. For this reason, the prop shaft and tube are a slight clearance fit, to reduce the amount of grease needed and to limit leakage should the stuffing box fail. As steel rusts, then the shaft should ideally be copper coated or flame sprayed with aluminium and then painted. Any exposed prop shaft between stuffing box and propeller or A frame is usually coated in epoxy, although I used to wrap ships prop shafts with fibreglass cloth and epoxy. Thorough cleaning and tarring is also recommended where appropriate. All sea end securing nuts and studs must be bronze or stainless steel.
If a brass or bronze propeller and a steel shaft, then always add a zinc collar to reduce galvanic corrosion.

Because the power from the prop is always aligned into the shaft, the rear bearing need not wear much as it does not take any sideways load and has minimal gravitational load. Therefore the bearings can be plastic on smaller craft where the thrust is taken by other bearings. Nylon uses water as a lubricant, or HDPE as used in hip joints can also be used. (In dirty or gritty water, then consider hard rubber).
HDPE (high density polyethylene) is found on most plastic containers and being thermoplastic can be carefully remelted to make excellent, cheap custom bearings. Bronze bearings are traditional for long life.
Prop shaft bearing dimensions are about 20 percent larger diameter than the shaft and about ten times as long as the shaft diameter. On small shafts a little extra metal does no harm for strength and on massive shafts, then these sizes can be refined. If making specialist shafts, always check the calculations to ensure the shaft or mountings do nothing untoward.
There is a wide range of prop shaft designs, but this is fairly easy machining and engineering design, where only the thrust and corrosion are of real concern.
The propeller shaft must be reasonably high grade steel and machined with good accuracy for the tapered ends to take the engine flange and the propeller. If not stainless, then the non bearing areas should be flamed with aluminium, nickel plated, epoxied or tarred regularly.
The engine end of the propeller shaft must expect the stuffing box to leak, so there must be a water drain before any expensive thrust bearing, and a tell tale pool in the bilge so the stuffing box leakage can be assessed prior to routine or perhaps, emergency maintenance.
If a long, thin shaft, then an intermediate bearing should also be employed, although this need only be a nylon bush snugly fitted into the prop tube to prevent the shaft from flexing and becoming damaged.

The ends of the shaft tapers are often 12:1 or 16:1 SAE or 10:1. If making your own propeller boss, then a morse taper reamer is probably best, then lathe or grind the shaft down to fit the propeller. The key should be able to take the power of the engine, but no more, to shear if prevented from turning, such as hitting a rock. In smaller designs, the key may be replaced by a shear pin. A Morse taper reamer can be used to make the boss, or made in an engineering shop: The propeller shaft can then be ground by hand while turning, to match the boss, although this is also generally considered a job for a lathe.
Before assembly, the propeller can be mounted on the bare propeller shaft and then balanced on knife edges.
Always fit a main retaining nut, and a secondary retaining half nut, or a suitable corrosion resistant retaining tab washer.

The coupling where the engine meets the propeller shaft must be carefully aligned, to ensure the engine does not misalign or wear out the coupling or gearbox bearing. The crankcase should be rubber mounted on widely spaced brackets or in firm rubber mountings. The coupling itself must allow for misalignment and this is usually a set of compressive rubber drive bushes between flanges and dogs or other similar type of connection. This will allow the engine to move a little, without applying undue distortion to the propeller shaft.
The propeller shaft must not be in any metal to metal contact with the engine, as this can cause galvanic corrosion and other problems. (See the Boat monograph for marine wiring on my website).
To ensure efficiency and long life, the engine crankshaft is aligned perfectly coaxial with the propeller shaft, even if the engine is mounted a tad high at the front.
The engine to prop shaft connection is checked with a dial gauge mounted to one shaft and they are rotated to check they are in perfect alignment or adjusted with shims under the engine mounts or other adjustments to get prefect readings.
Any misalignment caused by engine torque reaction of the engine should be eliminated by even spacing of the rubber mounts, either side of the crankshaft centreline. In all but racing situations, the manufacturers engine mountings are perfectly acceptable. For racing engines, the car manufacturers mountings are not designed for slamming between crests of waves and engine mounts must be carefully designed to support the engine and also protect any delicate hull design.
Where heavy torque reaction is encountered, then a rubber mounted head steady arm may also be required.
The engine must not apply fore or aft pressure to the propeller shaft (unless specifically designed to do so), but should only apply a rotating force. It is the job of the thrust bearing to apply the thrust from the propeller into the hull of the boat.

When calculating shaft diameters, remember that a fast revving 40 HP shaft can be smaller diameter then a slow revving 40 HP shaft. (e.g. 30 mm dia at 3,000 rpm, but 42 mm dia at 1,000 rpm.) Where the larger shaft diameter is needed to transfer the power of the slower, but larger propeller blade.

Outboard motors can be added if requested, but they are easy to work on and usually the province of 'boaties' who have them professionally serviced at high cost, enabling the locals to afford local homes.

Appendix 6. Thermal barriers and internal surfaces.

The best defence to condensation is to prevent the cold surface from meeting the internal damp air which causes condensation. Therefore the steel hull should receive a thermal barrier. The following can also apply to fibreglass and wooden hulls.

Prior to insulating, all windows and surrounding components can be protected with masking tape. The internal face of the finished hull should have the various cupboards and other fittings made in thin marine plywood, fibre glass then epoxy resined into place and built to make the cupboards, minor bulkheads and sections. Tubes are also inserted to carry the wires to the navigation and interior lights etc. Make sure the tubes are laid such that new or extra wires can be pushed through when needed. (See also the 'Boats' monograph on this website for wiring.)

Thick cardboard or light weight plastic or fibreglass panels can now be made to fit the gaps between the bulkheads, back of cupboards and other hull areas. The central areas of the card has holes cut in it and the card glued into position with simple cardboard spacers of about an inch. Expanding wall insulating foam may now be squirted into the cavity until fully filled. After about four hours, the foam has set and excess foam can be neatly trimmed and perhaps covered with padding or vinyl cloth or whatever may be needed. If there are any gaps, these can be easily filled.
Where such insulating panels are to be removed, which is highly recommended, the areas can be covered in food cling film before injecting the foam, and the removable panels can then be fitted with hook and loop fasteners, or double sided tape, or any other method of retention.
If injected directly, the foam will stick to the hull to prevent condensation of the steel. If removable, the foam will be a perfect snug fit to greatly reduce chances of condensation.
The advantage of injected cavity foam is that many little design flourishes for fittings such as recessed lights, electrical sockets and other subtleties can be made in card or partially countersunk to prevent damage. A little cutting, creasing and curling will give a piece of card with paper pipes to take the wiring, plywood blocks to screw the fittings, and a host of other stretches of the imagination. Soaking and light scrubbing will leave just the foam, ready for vinyl cloth or other fabric of choice. Hitting your head against the foam will do no harm in a rough sea.
Semi-structural components such as cupboards will naturally be fitted first. I sometimes integrate hand holds to the sides or edges of minor plywood bulkheads and such like.
For an even neater layout, LED lights and switches can be positioned in the card for perfect alignment over the chart table and many other places, with the wiring tucked neatly away, running through plastic tubes such as drinking straws before the foam is injected. These are ideal minor projects for the kiddies to do, and if they get it wrong, can be doe many times for mere pennies.
The roof can also be insulated in a similar manner using aerosol foam and cardboard templates or the much easier semi rigid structural foams. For deck heads where the head may hit, rubber strip or sheet such as camping mats can be employed to great advantage at stormy times when a cut head is least wanted.
I like to fit electronics in such compartments as they are less prone to vibration and shock and if they should be knocked against, as there is some leeway before breakage. It can also make a very neat, sculpted control panel in a yacht cockpit.

Emergency buoyancy foam is applied in all dead areas and wherever needed to ensure the boat will never sink. See also yacht keel test.

Other fittings.

All boats suffer from cramped spaces and therefore poor ventilation, especially in the tropics, so good ventilation which does not compromise safety is highly recommended. A good sleep in the tropics will need incredibly good ventilation. As hot air rises, then tropical sailing should include a roof vent or seaworthy opening hatch. In Arctic waters, then ventilation should be a small fan, ducted out from the colder bilge, as this keeps most heat in. If no electric power, then an adjustable, wind powered ventilation system should be employed. Any flame or fuel powered heating system MUST have good ventilation and always a noxious gas and a low oxygen warning device.
Always sew up some midge netting sheets to fit over all ventilation. Mosquito netting is acceptable but midges are smaller and more annoying, although not dangerous as some mosquitoes. This netting is cheap, so making up a very large sheet to drape over the boom and cockpit to give long, lazy and bug free evening meals and a much cooler sleep.

Seat coverings on boats must always be waterproof, so any foam under the vinyl of open boats should be closed cell foam. This is the same as good quality camping mats, although the cheapo versions should be steered clear of, as the foam compresses too much. The superior foam does not compress with age and is perfect. I still use some of the first Karrimats(tm). On many smaller boats, where cosmetics are not so important as functionality, then simply using camping foam will not only offer good comfort, it will also be resistant to slipping in wet weather and easily cleaned. Gluing the foam in place and then applying a sanding disk will allow almost any shape for any surface and some degree of sculpting to great effect. (I prefer mid blue Karrimor camping mats when they are available.) Ideal for seating on engine bay covers.

Seating on yachts, a personal viewpoint.
All yachts sail for a reasonable time leaning away from the wind, (often about 22 degrees, with the lee rail just awash) and yet, the seating is always designed to work in only the upright position. Only those siting downwind side have reasonable body support, but usually sea spray too, and a very poor view of the horizon. siting on the upwind side is always preferred, yet so uncomfortable.
I far prefer to have friends and crew sitting comfortably on a properly heeled yacht, so my seats are often designed for this too. It is not difficult to have the longitudinal seats with steep 'lean back' angles when at moorings, and yet still allow the crew to sit far more comfortably while sailing. Likewise, the seat base can be curved to make a bucket seat base, when seen in cross section, for stationary and also heeled use.
Swivelling seats are possible but not used, because the knee to ankle distance will vary uncomfortably. The other alternative is to have adjustable seats with the pivot under the knee area, so that they can be set in the heeled position and then returned upright while moored.
If adaptable seats are not wanted, then the access point where the crew step on bard, using the seats, then this little seat area could be sculpted for siting at a heeled angle, so at least one person can sit comfortably with their back leaning slightly back while sailing.
Make sure all those on baord can enjoy the experience and view, comfortably.

Toilets.
See also BS 7162.
Toilet facilities may range from a bucket in the forward hatch / slamming area, to a full toilet with shower.
Even on a day boat, a small toilet area should always be considered as a dedicated area wherever possible for some reasonable luxury, possibly with an integral shower, as most people spend time afloat and swimming in hot weather.
If making a primitive toilet, then considering fitting a controlled scupper so the dump area can be cleansed by the sea when motoring FAR off shore. Never discharge toilet waste within five miles of shore. Using two carefully designed seals, one as the toilet seat and the other as a flush fitting hull scupper, can allow even a low waterline toilet to be designed if carefully used.
Preferably fit a commercial toilet flush system. Always have dual underwater valve seals and the toilet bowl well above the waterline and sealed.
Toilets need good ventilation, so direct openings are often employed such as an opening skylight. This does not need to be the basic design so common on cramped vessels, but could also be a piece of flush fitting, sculpted polycarbonate with opaque mirrored sun filter.
For ultra compact toilets, the same compartment with the toilet seat down can become a sit down shower area, with a simple water drain to a separate sump tank in the floor and pump. This is not as effective as a full height shower unit, but a lot better than none at all in smaller hulls. (NEVER allow washing water to enter the bilge, only sea water and such like, otherwise the wastes may cause smells and disease). With a micro fine shower hose, a flush fitting reading light and arm rests for heavy seas, it can be a small, but an acceptably comfortable compartment. To save water, the shower hose should have a trigger similar to a garden hose, so when pressed, warm water is available. A simple pressure tank can be operated with a hand pump, again similar to some hand pumped garden sprays, or with an electrical car screen washer pump. Not difficult, not complex and not heavy.
Even just a shoulders width gap between bulkheads of a curved hull is all that's needed on a small boat and far better than a bucket in the forward bulkhead.
If there is no other space than a forward compartment in a very small yacht, then consider making a reasonable toilet seat or frame for a modicum of comfort. If the forward hatch is very small with cramped headroom, then the hatch can also include a polycarbonate bubble hatch, so a desperate member of crew can at least see when the next big wave is about to make life interesting. Always include arm rests or hand holds to help getting in and out the hatch when the sea is not helping. It is common for the forward hold to be a sealed compartment as this holds the chain and sails, ands acts as a slamming area should the bow strike something hard, and therefore it is sealed. In day boats, it may be an open compartment with an internal hatch, whereupon a rubber sealed access door for some slamming protection, and a small vent system is recommended. It is important to decide how the access to be done and ensure that it is safely accessible in all seas.

Exhaust heat.
Due to the Laws of Thermodynamics, all internal combustion engines loose more heat than they convert into energy. So for every calorie of energy from the fuel, more than half is lost. But some of this can be recovered from the warmed cooling system and the exhaust heat. On power boats, there is free heating available most of the time, - so use it to advantage.

As much room is invested in a toilet in a small boat, then it should also be for storing wet clothes and for drying, and as such could be close to the main hatch for certain smelly venting purposes.
Getting good, warm airflow through such a small compartment is accomplished in many ways, but direct ducting of hot air from around the exhaust into the toilet using a simple 12 volt computer or car fan, makes a toilet into a superb clothes drying cupboard, which can then vent to warm the rest of the cabin. This free hot air will require a simple duct running around the exhaust to duct warm air into the desired compartment.
Warning: NEVER allow any air from the engine area to directly enter the living quarters. All such ducting attached to the exhaust must have a separate inlet and a safe, carefully ducted system.
In very small boats, an insulated exhaust pipe could be run through a toilet area if positioned close to the engine area, using a stainless steel pipe with shielded radiator panel for heating the compartment. This can be shielded with a radiator panel to maximise the heat in the very limited environment of a boat. Although this exhaust pipe will be noisy, few people use toilets for long times, so noise should not be a problem. Make the most of what little there is. It may be a noisier toilet, but a warmer, drier one.
The other alternative is to use the engine cooling system as employed in most car systems, controlled by the engine thermostat abd duct warm water through the boat.

Remember: Making your life afloat more comfortable is where the bare hull with motor and the piece of chalk and plenty of time will always pay dividends in the years to come.
Knowing the ideal exhaust route and building a toilet or clothes drier around it is highly recomended. A good radiator system in a motor boat is not rocket science. It can be the difference between an acceptable life afloat and enjoying a comfortable life afloat.

Heating food.
See also BS5482 pt3.
(Decide where the cook is to shoulder or wedge themself on a rolling boat to be in safe control of the cooking.)

If cooking is to be done while moving, then always mount the cooker on gimbals so it leans as required. The gimbals should be damped to minimise problems. Using two washers with silicone grease between them and a sprung frame which presses outwards against the greased washers is a basic solution to excessive swinging. Or use simple pneumatic dampers placed between the bottom of the cooker and the bulkhead to help damp any design. (Even just a small tube and plunger using a modified kiddies push bike pump. The piston is slightly reduced in diameter or slotted to give a smooth damping action.)
If a powerful motor boat, then two axis gimbals are needed. For day yachts, a single axis may be sufficient.
Always have the mass of the cooker and the items for cooking positioned much lower than the gimbals pivots and fit foam rubber bump stops. Try to get the saucepan water level to be just below the pivots to reduce slosh.

Steel wire from old cooker frames, shaped to fit the pans on the boat can be made up in half an hour to secure not only the pans with the water level with the gimbals, but also swing, the cooker heads perfectly positioned below with wind and fire shields. Such a dual ring system using spring loaded pan holders is highly recommended for cooking in all but the worst seas. So start by making the gimbals and pan bas, then the pan securing devices, (keep the springs away form the flames so they keep their springiness) then position the cooker below, then fit this to the hull by making the support structure to fit with full swing and damping up to 40 degrees on a yacht. Never build a gimballed cooker to fit a pre existing bullhead if making your boat from scratch. Do it right from the outset and reap the definite rewards.

On motor boats, some cooking can be done in a heated compartment mounted on the exhaust, but usually requires a slow cook technique as the heat flow is not very good unless designed well or a large engine. Always use any exhaust cooking with a sealed pan such as a pressure cooker for safety reasons. A sealed pressure cooker ensures no exhaust gasses contaminate the food, should an exhaust leak occur.
An exhaust heater should use a stainless steel exhaust section which must be well supported with regard to engine vibration, with a means to secure it while motoring. A remote digital temperature sensor is cheap and allows cooking to perfection while keeping watch on deck. Done carefully, with due regard to exhaust contamination and regular inspection, there is nothing preventing a stainless steel section of exhaust to be shaped like an oven, with five of the six faces surrounded in exhaust gas, plus an insulated lid on top, for a good piece of roast beef or whole chicken. Although baking fresh bread or a Christmas cake will require a long, gentle days' motoring.

At a simple level on any engine, hot water is easily obtained by wrapping stainless steel piping around the exhaust, leading to a hot water storage tank. This is usually done with a hot riser pipe and a cool down pipe between the two fresh water tanks. The upper tank being a small insulated item for the hot water. Even a dozen turns of new car steel fuel pipe piping around the engine exhaust can furnish hot water on a motor boat. (Tip: If making sharp tuns on such a pipe, then fill the pipe with lead free solder to turn it on a former without suffering any kinks, then remove and melt the solder out. This is the same method of early Renaissance musical instrument makers. Make the spiral slightly small we then the exhaust pie itis to fit over, so that it makes a nice thermal contact, then insulate so the heat is transferred to the water, not the surrounding air.
For small motor boats and yachts, then direct heating in the exhaust is preferred, but demands stainless steel to prevent long term damage. This can then supply a hot water storage tank for when the engine is silent. A solar heating panel is also recommended for living aboard for many days, and insulating the hot water tank will enable a dead space in a deck head to be fitted out as a small hot water tank.

Most cars have an internal heater element and fan, so the same system can be used for many purposes on a boat.
If the engine is a marinised car engine with intercooler, then the plot is simple. The hot water surrounding the engine should be able to be pumped around the boat to old car heating panels and to warm a hot fresh water heater.
Warning,: If using a two way valve to re-direct cooling water from the sea water intercooler, to heat the internal spaces of the boat, it is important to never force the engine cooling water through all the radiators in series, but always in parallel. A car engine water pump is NOT up to the task of long lengths of small bore piping on a large boat unless the plumbing is large bore, otherwise this constriction of flow may prevent cooling water from circulating enough to cool the engine, especially in warm weather. Only use a similar restriction as found in the standard car heating system, so the thermostat works correctly and the engine will not overheat. In most cases, just the one car heater element and 12 volt fan should be used. Always employ the thermostat system as fitted on all car engines.
The safe way is to allow the car thermostat to work as needed, and tap off coolant for heating as used by cars. A hot water switch between cabin and dry room / toilet heaters is also possible. Watch the engine temperature gauge when testing.

Appendix 7. Hydrofoils and Ekranoplans.

Appendix 8. Trailers.

Making your own trailer is not difficult, as it is simply a case of buying a pair of (commercial or scrap yard) wheels on suspension arms and a couple of long rectangular box sections, adding a cross beam and welding it all up. The rest is detailing and is where a trailer becomes a good or bad design.

The whole point of a trailer is convenience. Yet so many trailers make life difficult. The owner should drive to even the slipperiest and steepest of slipways, reverse, and tie off the trailer if slippery. Then roll or winch down the boat to launch, using the trailer brakes. Then tie off the boat and winch the trailer back up to the park to stand it on its end so that it takes up minimal room, especially if away for a few days or more.

A trailer is merely a means to support the boat on the road and while entering and exiting the water. It is not rocket science, just a jigsaw puzzle of simple moves. The design should allow the boat to launch, without having to get your feet wet.
Many get it wrong and get wet feet.
If a small yacht, then the keel should be retractable for obvious reasons as this solves so many problems.
The next problem is launching it. Many trailers have the hull up high, but unless you are transporting across rough ground, then the ground clearance need be no more than the average car. This is about five to eight inches, and if the keel is supported at this point, then with two main trailer beams, then the trailer need only go a very short distance into the water on the slip way to launch.
Lowering the trailer wheels is not necessary, unless a difficult launch where the nose raises far to high for comfort or may swamp the transom. In most cases, a winch is used to lower the trailer and boat into the water and also to retrieve it. To ensure easy retrieval, the trailer should have a bow guide post so the hull supports will align correctly. With a bow painter hole, the boat can be pulled perfectly into alignment over the sunken trailer.

As can be seen, the main requirements are three fold, on the road, in the car park and on the slipway.

The trailer should be designed like all trailers and caravans, to support the load in a balanced manner.
Theoretically, the wheels should be close under the centre of gravity of the boat for good road holding and balance. In practice a caravan has its load just ahead of the wheel for good handling. A boat trailer has its wheels slightly more to the rear as it is usually 'in a rear down alignment' on a steep slipway, where the centre of gravity must always be forward of the wheels, as such angles and downward velocities and rapid or uncontrolled deceleration, can cause a loss of control.
The further the centre of gravity is from the wheels, the worse handling the trailer will be. Good balance helps good handling and also makes fitting to the ball socket easier. This requires a good compromise or a very gentle slipway.
Suspension must be matched to the combined weight of the boat and trailer, so that the ride is safe on the road and minimal damage to the hull.
The trailer must also be manoeuvrable.
The trailer must also be safe to use and this often includes a winch for launching and for hauling back up the slipway, especially when a slimy slipway prevents car use.

The hull is supported underneath on pads or roller to prevent movement. To assist some launching, these are usually rollers if the trailer is needed at low tide, where the trailer cannot clear fully under the hull and the winch is needed to drag the hull into place. Use pads on a delicate hull or where the slipway is deep or you plan for higher tides.
As rollers make line contact, then they should be moderately hard, spongy rubber and wide, so the force is spread across much of the hull, especially if wooden or GRP, as this localised force on rough roads can lead to premature fracturing from these localised stress points. The rollers are also pivoted to take up the changing shape of the hull as it varies on its short roller journey up the trailer.

Many people prefer not to trust slipways very much, especially when they are steep and slippery. Therefore a cable assisted launch using any of the slipway tying points can be used with a winch to perform the launch under full control and for easier later retrieval. Even a two man yacht can be dangerous on slipways.

As you may have guessed by now, launching and retrieval can be a hassle. So getting the design right from the outset is going to make the difference between a good day out and a very good day out.

Folding trailers are useful where parking space is limited.
Being able to place the trailer behind the car and back up close, and lock it to the car is priceless if you are polite and only need one parking space, or the trailer and dinghy park is almost full. Therefore the rear of the trailer, beyond the wheels should fold up, or if a solid design then the number plate can be easily removed so the trailer will stand end up or be laid on its side.

The main road section is often triangular in platform to take the towing load and load the support wheels correctly, with a low central beam to enable strength and a low launching and retrieval waterline. This cross beam is the limiting factor and cannot be compromised, therefore it should be particularly strong, and if using a single type of rectangular steel tube for the trailer.
It is important to have brakes on the wheels and this is particularly problematic with sea water, so the rear brake plates must be an open design to allow them to be flushed with fresh water at the slipway or upon reaching home. Being able to slowly push the trailer down the slipway for launching, using a good hand brake to control the descent is priceless. Using a winch for retrieval can be much easier especially if the brakes are good and the trailer has a neat steerable and large nose wheel.

Making a trailer.
Raise the hull up to be 5 to 8 inches off the ground, depending upon the types of roads you normally encounter, plus a couple of inches for the thickness of the axle cross brace and any suspension movement if a solid rear axle. If separate wheels, fit the wheels at the same track (width) as the towing car and directly under the centre of gravity of the boat.
To find the centre of gravity, roll the keel on a single piece of steel tube until it balances. Now move the wheels back slightly to apply just a small load to the front of the boat and trailer combination - enough weight over the front to be able to be lifted with reasonable effort using both hands.
If encountering steep slipways, then move the wheels back further until it safely balances at about the same angle as the steepest slipway. This will ensure the trailer will not tip down on the tail when launching on a steep slope and if a rear wheel drive, will not unweight the car's rear wheels and cause loss of traction. Seriously consider an anciliary retractable tail wheel for launching if having tipping problems.

Between the wheels will be a cranked or built up cross beam. This can be made from two or even three cross beams for strength depending upon the type of suspension.
As the keel is going to be above the cross beam member, the keel can be designed to sit just an inch above this cross beam, supported to take the keel and hull pads.
The suspension is now welded in place and will be adjusted later. If using a small boat, then a real rear Mini subframe may well do the job,(check the permitted axle loadings) and any steering should be welded to track straight ahead. The hydrolastic cylinders can be cross connected, then pressurised to suit the hull mass at a later stage for best handling.
If using an old van rear axle, such as an Escort Mk 4 van, then this is very straight forward engineering and the leaf springs and shocks can remain essentially as they are. Don't forget the Panhard rod, although this can be positioned lower to clear the keel. Any moving (unsprung) cross tube between the axles must be checked so that it does not touch the keel at full compression.

With drum brakes, always remove or trim down the brake backing plates, which are just dust covers, so the brakes can dry out quickly and can be hosed with fresh water.

The front end of the trailer is not yet made, merely steel tubes extending towards the front.
If a pointy speed boat, or where the bow is mostly fresh air and the weight to the rear, then the rear of the boat is easily carried much further forward than normal hulls, with the bow over the car boot (trunk) to maintain the centre of gravity of the trailer ahead of the trailer wheels. This would keep the centre of mass of the boat and the trailer more manageable than any long trailer.
If this is not possible then get a sensible boat, as the pointy bit of a power boat can damage coach drivers, and motorcyclists. Any pointy bit sticking back must be fully protected with a steel crush frame and structural foam, tail lights and a number plate deigned to mould around the pointy end and fully secured in place.

For proper boats, the hull is fairly evenly balanced and the supports will be evenly spaced around the hull. Because the hull must be secure, then the support rollers should be evenly spaced around the middle of the hull and preferably line up with internal bulkheads to prevent distortion over winter and any rough roads.
Rollers will need to slide as the hull sit in place and these are normally pivoted, not only for the vertical angle, but also as pairs to ensure the pressure on the hull is even across all rollers. For this reason, four rollers each side are common, and consist of pairs of rollers on pivots.
The shape of the hull must now be supported. If a low trailer, where the hull is close to the ground, then pads are often all that's needed.
The main supports will be pads or rollers. The rollers are not needed and only pads need be used in many cases, and this is acceptable if the bow is aligned perfectly with an alignment slot on the trailer upon recovery, and perhaps a side post for perfect gunwale alignment, especially if the slipway is not too steep, whereupon the pads will align nicely.
The hull is now carefully slid into the trailer and adjusted for weight distribution. The keel is lifted slightly off the cross beam, or a steel channel slid underneath any suitably shaped keel for support and to help alignment during retrieval. Any keel channels should include smooth keel guides for underwater assistance. Line them with sheets of nylon (or old HDPE plastic) for a smooth entry with no damage. For round hulls such as modern racing yachts, where the keel is removable or lifted, then there may well be no discernible external keel line, so a couple of demountable stern guides should be added to the trailer. A bow marker slot is also recommended for alignment under water or a bow painter and guide ring.
When making the pads and pivot arms, note how the hull is designed to be supported in the water and therefore all structural support will be below the waterline, as this is how the boat is designed. Mark the bulkheads in crayon on the outer hull and attach hard rubber pads with a little masking tape or sticky blue office putty. Use pads as large as is deemed suitable to take the load. If a delicate hull such as thin skin aramid and foam jobbie then use larger pads or even make them from spare sections of aramid and resin to match the hull.
I prefer to make any rollers using different densities of foam to ensure the hull remains well supported. Hard rubber central, then closed cell camping mat and a hard rubber outer from old truck inner tubes.
If a fairly strong steel hull then smaller pads or moderate rollers are perfectly adequate. For better support, the pads can consist of large rubber pads on a large, strong plywood plates.
Pairs of pads are supported with steel pads or strong marine plywood backing plates, dependant upon what scrap material is left after the build. These are then linked together on an arm at mid point, which is then supported on the trailer. The pivoting arms are limited in their movement to ensure the retrieval is easier. Four or more arms are common. The pivoting of these need only be lightly restrained pad security devices, as they are only used in compression and kept from floating away if made of wood. Therefore the pads need only sit in simple sockets or restraining clips or even nylon locking straps or other simple methods which allow the pads to align flush with the hull and to adapt to the hull shape. Any floppy pads can be simply held in position with bungees.
Never use just two arms; as this would enable the boat to move about when travelling and must not be considered.

The boat must be secured and this requires long industrial straps. These can either be attached to the gunwales or across the whole hull and will depend upon the design of the boat. Never over tighten straps, they are there merely to prevent movement and must not apply any excessive pressure on the hull, especially if a lightweight composite racing yacht hull. Secure, but not constrictive.

Try make the trailer no longer than the rear support pads. If the rear pair of support beams beyond the axle can be removed or folded for easier storage of the trailer, then all the better. A separate bumper and number plate structure can be added to be vertically level with the stern, or clamped to the transom so that any reversing problems are prevented.
There are mandatory regulations on heights and spacing of rear lights on motor vehicles and must be observed.

Where a battery is fitted for the trailer winch, then this can also be charged up while on the move, especially when travelling to the first launch of the year. If you have problems, then also include a boat battery charger on the towing wiring system so that both the trailer and the boat batteries are charged. Soon after winching down into the water, you will need the boat motor to start for manoeuvring off the slipway, so charge up both. See also 'Boats' and 'Batteries' monographs on my website, which discuss boat wiring, battery maintenance and charging.

The keel need not be supported unless making a very small trailer for a simple small motor boat, whereupon the keel slot can be the main structure with simple pads either side for secondary support.

Trailer nose wheel design.
Most people just buy the usual crap trailer nose wheel which is just there to seemingly prevent it falling on the ground. Sometimes they don't even manage this and many trailer nose wheels are a disgrace. Their boats are often not much better.

If the nose wheel was fitted in a bracket such that it folded down to keep the boat level, and it included a strong steerable tiller, or a pair of handlebars from a motorcycle, and these in turn had brake levers to control the left and right brakes, then the trailer could be pushed, braked and brake-steered down a shallow slipway under far greater control, often by one person. It is even easier if using a winch controller mounted on this tiller.
The brakes are connected to any steerable nose wheel and tiller or handlebar, then the cables adjusted. Always make sure the trailer brakes act through the ball joint on braking with the towing car. To operate them on the slipway, just add a secondary lever to the sliding ball joint brake connection, so that the towing car and also the nose wheel tiller can apply the brakes independently. If you have brakes then use them - it is not rocket science.

Trailers invariably get sea water in all parts and therefore the steel must be corrosion resistant. Galvanising is the most common, but can cost money. Spraying with aluminium at the same time as a steel hull is being prepared may be cost effective. Otherwise, the trailer must be well painted with a zinc based paint and preferably the internal tubing sealed. A good way to prevent internal rust is to exclude oxygen, so the internals are painted, allowed to dry, then squirted with a can of squirty builders foam to fill up all the internal voids.

Once the boat is on the trailer, the suspension can now be adjusted where available to match the load. Many people never bother with this and have appalling handling when towing.
Suspension adjustment is done by bouncing up and down on the trailer with the boat, so the suspension moves. A heavy boat will be stiffer, and a small racing yacht will be easy to bounce. Always make sure the suspension is damped and only bounces one and a half strokes before coming to rest. Adjust the position of the shocks or fit lighter or heavier dampers. Alternatively if basic dampers, rebuild with different oil or drill and flush and refill appropriately. If the springs are wrong, then look for similar items off lighter version of the donor shocks or pack the springs to preload them using spacer rings under the springs to stiffen the effect.
If in doubt, get someone else to drive while you look out the rear window of the towing vehicle and make notes, or preferably be able to adjust the suspension on a long run with many adjustment stops in lay-bys.

The tail plate and lights are simply fitted with quickly detachable connections, so add little C clips along the trailer to retain the 7 core trailer wire. Far too many prats have the trailer cable dangling near the road. Rings of steel coat hangar wire are wound around a bar the same diameter as the trailer cable wire to make the C clips. The rings are slotted and welded to the trailer to secure the wire. If aligned correctly with a small gap, then the wire to the tail plate and lights will be secure, yet easily removed to prevent theft.

Any battery box and winch is made to fit a removable but secure fitting, with just a simple slot to take the winch load. This simple fitting can ensure the winch and battery pod can be easily stowed in the towing car when parked to prevent theft, now so prevalent in modern Britain. A solid bar can allow the battery and winch to be easily dropped on the front of the trailer, restrained by a big R clip and swivelled to both pull up the boat onto the trailer if low tide, and then to pull the trailer up the slope. Then put back in the car. Add a small box to hold the remote control and a shoulder carry strap to make a very neat arrangement.
Manual winches also available.

Theft in modern Britain is on the increase, as if low standards are being imported to Britain. The days when I could safely leave a trailer tucked away by the slip way are long gone. So the trailer should be locked to the towing car, preferably by putting the trailer upright against the wall, reversing onto it, then chaining them together. The battery and winch and tail plate must nowadays be stowed in the car.

Always wash the trailer brakes after use. Remove brakes and inspect before each season. As the back of the brakes are accessible, a LITTLE spray of silicon maintenance spray over the brake pivots and cables is recommended just before winter, but NEVER on the brake drums or brake pads. Cover wheel and brakes in plastic bags from the rain, but allow air to vent any moisture. If possible block the trailer and boat up off the tyres over winter. Take the winch and battery pack along with the boat battery to the garage or room under the stairs for weekly trickle charging using a simple 7 day timer on the battery charger. (See batteries monograph.)

Appendix 9. Autopilots.

Autopilots are becoming more common and the better ones are integrated into GPS systems to allow the user to include way points or to navigate to a desired position.
The earlier designs simply used vanes at the back of yachts, to keep the boat at the desired direction to the wind and thereby allow the solo yachtsman to get some kip.
Moderate sized yachts can use non electrical systems, where the vane operates a servo style system, where the vane directly controls a pendulum rudder, such that the rudder which hangs over the stern in the flow of water, such that it can then apply a much higher force to ropes which in turn control the rudder. Smal boats may get awsy with a large vane directly controling the rudder.
In all cases, the sails must be trimmed so they are balanced and the boat sails true to the course, so the rudder can be left alone for ten seconds, with the boat sailing in a neutral balance on the desired course. It may be preferable to reduce the sail for a moderate and safe headway rather then the normal pace.

The rudder control of a small yacht can be easy, as the control system simply replaces the hand.
The simplest is to fit a massive wind vane to the rudder or rudder linkage, then angle the vane relative to the rudder and hope the wind stays constant and powerful enough to keep the rudder on the desired bearing.
At the simplest level, a basic autopilot can be done with ropes from a large wind vane over the stern, to pull on the rudder or steering wheel.
In some cases, the main rudder can be lashed amidships and a smaller rudder at the stern is employed acting purely from the adjustable wind vane.

Making your own autopilot is not recommended as it must be fail safe and bring the boat to a stop and deploy a sea anchor if near the coast or the echo sounder notices dangerously shallow waters.
For most people, the simple vane control is connected to the rudder using a temporarily connected motorised actuator so that the vane can keep the boat at a set direction to the wind.
If there is a GPS system with control output, then this too can be employed if a power tiller is added.

For yachts with electrical power and free rudder arms, then a temporary telescopic rod can be attached with one end to the gunwale and th eother to the rudder, along with a motor and telescopic screw thread and gearing. An old 12 volt car seat base adjustment unit will often do. The control can then rotate the motor according to the desired direction set on the vane, using simple micro switches. The whole rig must be well made, as you may be asleep, so using over specified items with high reliability is important, as it plenty of testing and regular inspection.
The steering control can be either connected to a compass or a wind vane to maintain the desired heading as required in relationship to the wind.

For a motor boat, a wind operated autopilot is often useless, although posible if steaming in constant winds. Therefore a powered system is needed and connected to a compass or other control system. The ships wheel can be connected to a push bike chain and sprocket arrangement and a geared motor to control the steering. As some steering linkages are heavy, then a strong control motor may be needed. Preferably use a motor without permanent magnets to make manual control easier. (See my wind power and wiring monographs on this website.)
The rudder control motor is bi directional and controlled by a simple switch arrangement (or by a more involved op amp electronic device). For most purposes, a simple design is best, not dissimilar to stabilisers mentioned earlier. The yacht vane is mounted to the hull such that it can be set relative to the hull and when the hull turns, the vane will actuate either port or starboard micro switches.
A similar arrangement can be mounted to a compass, but always use optical sensors (such as out of an old computer mouse) for left or right, so as not to disturb the compass itself from either direction nor from electro-magnetic interference. Use a special compass or modify a spare one with a pair of hall effect sensors or to optical sensors on a movable ring. Two sensors are used, so that if you veer to port, the port sensor to one side of the desired course setting will activate the motor one way, and vice versa.
The sensors will then operate the motor in either direction, through relays, to adjust the yacht direction relative to the wind or compass setting.

Because there may be plenty of fluttering in such systems, then some simple damping in the control loop is recommended, such as silicone grease on the wind vane pivot or a slow moving motor to 'damp' the system to enable smoother control.

Always check the autopilot by making it work for a few hours, to settle into the present conditions and perhaps fine tune it to your needs of the next few hours. Then make sure the battery is fully charged before relying on any powered auto pilot (and perhaps keep well away from main navigation areas) before getting a kip. Always have a good radar reflector and perfect navigation lights, then sleep, but be ready for any unwanted sounds.
Having a dimly lit heading repeater above your bunk, within eyesight whiteout lifting your head, with a yellow sticky note with the bearing in bright felt tip, beside it will allow you to cat-nap with greater confidence.

If a rudder with tiller, then the tiller can often be tilted back over the transom and connected directly into a simple windvane autopilot lever system.

Hydraulic pumps and motors.

The varous forms of power units are often a simple hydraulic pump driven from the end of the crankshaft, via a valve block to control a hydraulic winch motor. Normally a sealed system connected by two pipes.
Hydraulic systems can also be used in larger boats for weighing anchors, steering, cranes or other equipment.
If leakage is noticed, top up the system with specialist oil, when the engine is stopped, then repair back at port.
(Safety systems such as deploying lifeboats should always be done by gravity or other fail safe systems, although general purpose boats on ships can often be lifted back into position using hydraulic motors, often driven by an ancillary engine and generator.)

For smaller boats, hydraulics is still a good idea for some items, but with a single engine, then when stationary, the hydraulics will not work, so an electrical alternative will be needed. To power a hydraulic pump when the engine is not running, then a secondary pump can be used, powered by electricity and storage batteries.
The smallest is from old convertible car automatic roof pistons, motors and pump systems, but rarely up to the use of heavy work, but may be useful for disabled sailors for secondary items.

For medium boats, a purely electric winch can be used, simply using the components from winches as used on the front of off road cars.
Where the crane has a leaning jib, then this can be operated by a second winch with pulleys to give the extra force, or preferably use a hand operated hydraulic arm as used in garages for lifting car engines. These are then fitted on a dedicated swivel built into the hull, with a smooth action and a n anti swivel brake, or multi position swivel lock, so that accidents do not happen when the boat rocks. I prefer a circular ring at the base, with a strong locking arm with indents for the various positions that the arm needs to take.

To lift an anchor chain, then a special 'chain pulley block' is available almost anywhere second hand. This can be easily done by buying such a chain block and replacing the manual side with a winch motor. for small units, then a simple groove pulley can be welded to accept a chain, but always make sure the pulley will take full lengths of links about the internal circumference, otherwise, spacing it out until it takes pairs of full links of the chain.

For those who have fitted a modern car diesel engine, then it may well have all the fittings for power steering and its pump. Such car hydraulic steering pumps can be employed to hoist small cranes and such like if designed properly and have a suitably large hydraulic fluid reservoir rather than that used on the car.
Likewise, any air conditioning fitting on the car engine can be used to power a refrigerator unit.

Few if any of my friends resort to buying specialist equipment, as the marine industry loves to make money from the rich fools and 'boaties' that abound and often spoil the water for the rest of us.
I rarely use specialist marine equipment and have never had problems. I suggest you too, consider the options when afloat. Whether competition sailing, or motoring or cruising under sail, you will save money and have far more options then the standard, expensive crap you see at boat shows.

Pets:
Whether a ships cat or a small dog, they should be able to go from cockpit to cabin with no hassle and preferably on carpet or special anti slip decking to prevent slipping. They should also have a favourite spot, so keep an eye out for it over the following months and pad it out accordingly. If it's up on deck, then add a comfy piece of synthetic, mould resistant carpet for them to sleep on. For toilets, train them to go on a piece of washable plastic carpet in a shallow plastic tub mounted appropriately, which can be dragged astern to wash for easy maintenance. Drinking and eating must be carefully checked, especially floor mounted drinking for yachts.
I don't know of any self inflating pet lifejackets, so adapting a kiddies buoyancy aid may be possible. (See also build your own lifejacket on my website.) Likewise a jack line fore to aft for the pet and its harness is highly recommended when at sea. Consider adding a personal alarm to warn when the pet falls overboard when the jack line is over tensioned. Any harness must not cause the animal to suffer unduly such as difficulty breathing, constricted movement or drowning if dangling overboard or dragged behind.
A barking dog is a right pain to others, so never encourage unwanted barking, so that any barking should be a cry for help.
If they can swim, as with many dogs, then always add a stern crawl point, then swim with them regularly so they know exactly how to get back on board a moored craft.

Hope this is of some use.

I have only skipped over some of the main features of making your own boat, but I hope this gives an insight as to what is involved and hopefully re directed you from simply going to another boat show with a wallet.
I hope you never become a boatie, but preferably to look at a life on the water with both open eyes.
Hopefully you may even begin to start boating or sailing properly, and do so safely, with economy and much greater enjoyment.
I also hope you never become yet another of the appalling 'boatie' prats so prevelant about our coasts and waterways.

Best wishes.
J.P.
Gizzajob or a post grad.

Unable to find work, (white British male over forty) I have been looking to do a post grad in composite structures and active keel design for twenty years, but there are no universities who are interested. (I've a couple of good degrees, one in technology, one in Science.) My local Uni gladly takes foreign students who do some really appalling work, whereas we local folk only get to watch.
Some of my friends who were better than their lecturers - not difficult in Britain - now often write final work for students, including post grad stuff, as it's the only work we Brits now seem suitable for.
No wonder a modern British degree is now considered crap. British education should be so much better than this, perhaps one day, even something to be proud of again.
If you know of any suitable university overseer who can help, please let them have my email address as I'm desperate to do a post grad in keel and hull design and yacht safety. I have various completed works on these and similar subjects, but cannot publish as they include patentabel items, and may not be usable as post grad theses material unless it's my own unpublished, original work.
Therefore, like so many British ideas, the more interesting stuff may never reach the light of day unless someone helps others.
Please help.

Please, please help.

J.Partridge. B.Ed. B.Sc. M.I.Plant Eng. etc.

See also website for other boat related sfuff -
Boats monograph for boat wiring and lots of other stuff.
Composite frames monograph for vacuum bagging of composites.
Camper van monograph for some interior design.
Motorcycle monograph for linkages, brakes, seats and cables.
Lifejacket and solar stills monographs.

As an apprenticed marine engine fitter etc, I've applied many times for a job as a fitter or labourer at local marine firms in Plymouth England. I have been un