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, s