Please donate if you find this site useful.
Fay Marine
Yacht Plans
Anchors & Anchoring
Battery Desulphation
Diesel Fuel


Free Fire Design

Interesting Sites

Good Companies

Other Companies

Junk Rig



Outboard Oil

Roll Damper / Flopper Stopper

Sea Cocks

Toilets / heads

Simple Holding Tank

Steel yacht F.A.Q

Wind Vane steering

Wind Generators

Yacht Legs




Steel yacht building questions



Frequently asked questions answered by Paul Fay


Why steel?


Steel yachts are growing in popularity around the world for several reasons. The strength and security of a steel hull gives great confidence. The ability of a steel hull to withstand damage when grounded or while moored with fishing boats or other commercial craft is becoming legendary.


The problems of steel rusting have been overcome as paint technology has improved. A steel yacht is now totally protected with modern paints, in fact many steel yacht owners think of their boats as a steel hull inside a plastic one. (The paint)

The improvements of paint have meant that the traditional extra thickness of steel allowed for corrosion is no longer needed. This has led to a reduction in the weight of modern yachts, so that modern steel cruising yachts can compare favourably with those built of other materials in both weight and performance.

The cost of a steel hull is very competitive when compared to other materials and the price of steel has remained constant for several years.


The cost of the materials alone to build a 35 to 40ft yacht hull and deck is around £4000.00 ($6400.00 US) (UK prices in 1998). This makes the cost of a steel hull particularly good for the home builder.


There are many other reasons why an increasing number of sailors are choosing steel, they are;


That steel is an easy material to use;


A yacht can be constructed quite quickly with steel;


The home builder can build in the open, saving on the cost of shelter;


The climate will have little affect on the steel during construction;


Very little previous experience with using steel is needed;


The maintenance required is not great;


The re-sale value compares favourably with other materials;


Steel is usually readily available although you should check in your local area;


Some companies offer 'kits' of pre-cut plates that can be assembled very quickly (although these tend to be expensive);


Some designers offer their plans with detailed sets of measurements allowing you to pre cut your own 'kit' of plates (this only adds a little to the cost of a set of plans)


An added advantage with steel is that if you are planning to visit 'out of the way places' then steel makes the perfect construction material as there is always a vehicle garage with welding and cutting equipment that can be utilized for repairs or modifications.


Alternatively, a modern 'inverter technology' welding set can easily be carried aboard. These welders are really small and light weight but are now being used in shipbuilding yards during the initial construction of yachts and fishing boats. They are easy to use and only need a suitable electric supply.


What about insulation?

Most steel boats are lined. Usually with plywood, which is fixed to battens fitted to the frames or stringers. This leaves an air gap that can be filled with some fire resisting insulating material. There are several materials that are suitable. The very best insulation is to spray the inside of the hull with expanded polyurethane foam before fitting out begins. This is a good system that also adds to the protection of the steel. Where fittings need to be added on the deck the foam has to be cut away and then under the fitting the insulation must be made good with rockwool etc.


Commercial shipping and large yachts are lined with slab rockwool that has an aluminium foil fire/moisture barrier stuck to the inside face. This can be used to good effect on smaller yachts although it can soak up bilge water etc. so attention must be given to this. There must be a moisture barrier covering the rockwool otherwise condensation will pass through the rockwool and condense on the steel. This will either be the foil or plastic sheet can be used but ensure there are no gaps.


Household fiberglass type insulation can be used but the continual movement of a boat can cause fiberglass dust to enter the accommodation and cause irritation to sensitive crew. It will need a moisture barrier to stop moisture passing through and condensing on the steel. This barrier can minimise any dust entering the accomodation.

Various other slab foams can be stuck to the steel but they are difficult to use as they tend to be rigid and the steel will have a curve.


Are steel yachts hot in the sun?

No, often steel yachts have better and thicker insulation than vessels built of other materials. As this is the case, by keeping a normal airflow through the yacht it will often keep very cool. Conversely in the colder months and climates a steel yacht is easier to keep warm.


How do you maintain the inside after building?

The interior surfaces of the steel will not need any maintenance, apart perhaps in the area of the bilge, if the vessel has been built and painted properly from the start. All stringers must have adequate drain holes to allow any condensation to drain into the bilge and the surfaces must be painted with a good coat of a modern paint, such as coal tar epoxy which is a really thick paint that gives excellent protection with minimum coats. Experience has shown that it is best to brush paint the inside as this ensures that the paint is forced into all the corners and behind any frames where they don't touch the hull plating.


What type of paint?

Wandering onto the subject of paint has bought us into a very technical area. But many of the problems start long before the paint is applied.

This is because it is not appreciated just how important sand blasting (see section later) and rounding off the corners is. If you take a winch handle and tap the middle of a painted sheet of steel you are unlikely to damage the paint. On the other hand tap the edge or a sharp corner and a large flake of paint will fly off. On the deck and especially in the cockpit area it is well worth rounding off all the corners by the use of round bar edges, or by using tube to form the corners of cockpit seats and coamings.


There are many types of paint available but at the moment the best seems to be to paint the whole yacht with some form of epoxy system and then apply a cosmetic UV resisting finish over the topsides and deck with an antifouling primer and antifoul below the waterline.


Some countries are now very environmentally sensitive and are restricting the types of paint that is available so a check with the suppliers will be needed. If you are building a steel yacht from scratch then it will be worth shopping around the commercial suppliers and buying in bulk as this will save money. (ask a local fishing boat skipper who the suppliers are)


Any experienced steel boat owner will tell you to use good quality paint inside the yacht. This is the area where it is very difficult to maintain the paint system. I always use coal tar epoxy inside as a good thickness is obtained with only a few coats. (We apply two thick coats by brush)

If you already own a steel yacht that has internal paint problems, I have often overcome them by spraying the bad areas with 'Wax oil'. Exactly the same as is sold to treat inside the panels of motor cars.


Another area that paint often fails is around the water-line. This can be caused because sometimes two different paint systems meet in this area. For instance, perhaps the topsides are painted with epoxy resin while below the water-line epoxy tar is used. As they are both epoxy you may think that they are compatible. WRONG! They often use different solvents and the epoxy resin needs to be taken well below the water-line. Allowed to cure and the solvent to evaporate for several weeks before being sanded and overlapped with the epoxy tar.

Take the paint manufacturers advice, and stick to it.


What about sand blasting?

There are several materials that can be used to blast the steel. Bead blasting is employed in large machines that plates of steel are fed through to pre-blast it before building. These machines normally also spray the steel with a holding primer. On the outside the weld seams will really need re-blasting and it is best if all of the outside is 'wash' blasted by standing back with the blaster and slightly roughening (refreshing) the blast primer prior to final painting. The seams and plate of any internal tanks will need treating in the same manner. The other internal seams will be fine if they are carefully wire brushed.

Sand blasting, as it's name implies uses some form of sand to prepare the steel. It normally produces a reasonable profile, depending on what sort of sand is used.

Grit blasting uses a very hard substance such as 'crushed copper slag' and produces the best surface. This should be to SA2.5 (near white metal. (See Yacht photos 10)


When building a steel yacht from scratch it must be decided whether to order bare plate and grit-blast after construction, or to have the plate blasted and primed with a holding primer before delivery.


Working with bare plate is dirtier than with pre-primed plate, but you don't have the problem of having to 'stripe in' the areas of damaged primer at the end of each working day, or the worry of how long the primer will protect the steel, a consideration if building the hull is planned as a long slow project. With bare plate the whole hull and deck, inside and out, will need grit-blasting and priming.


Doing all the work yourself, hiring the equipment and buying the sand will cost considerably more than having the steel supplier pre-blast and prime it.

The inside of a hull built from pre-blasted steel can simply be cleaned and painted but externally around each weld, re-blasting is really the best way to achieve long term protection.


I have never found 'striping in' the areas where I have damaged the primer by cutting or welding to be a problem, I just allow a few minutes at the end of each work period for this job. In practice if the steel has a good coat of primer it will last for several months in the open, before there is any sign of rusting. Check with the primer manufacturer what the maximum over coating time is, as some primers need painting within 6 months or a year. If this is the case some primers can be re-activated by painting on a second coat of primer. This ensures that subsequent coats of paints adhere well. Don't forget to order extra primer when ordering the steel, probably about 25 Liters ( 5 gallons ) will be sufficient.


Is Metal Spraying worth doing?








What about 'filler'?

The use of filler on steel yachts has acquired a bad reputation due to several reasons. In years past poor building methods leaving deep hollows to be filled, the use of polyester resin filler and poor application methods have often caused the filler to fall off.


With proper building techniques only a small amount of thinly applied filler should be needed in the area of welds etc. Above the waterline polyester seems fine but below the waterline epoxy filler should always be used. following the manufacturers procedure. This can entail painting the area to be filled first, then filling and fairing before painting the whole yacht. With the correct materials and procedure the use of filler is acceptable.


'DIY' Boat building, can 'I' do it?

The answer is a resounding YES! There are very few skills used in building a yacht that can't be utilized by the amateur. For instance the welding required to assemble a steel yacht is minimal. The whole hull can be 'tacked' together and when assembled then a professional welder can be employed, for a few days, to solidly weld all the joints.


How much will it cost?

This is a difficult question to answer as it depends on how much of the labour is supplied by the builder or the family. Without any labour charges it is surprising how inexpensively a good yacht can be built. For instance in 1995 I completed an ocean going yacht for myself that I subsequently sailed from England to the Azores, The Canaries and back to England, encountering several gales and two storms. This yacht cost £18000 ($28800) for materials, which included GPS and SW radios etc. This cost represented less than a third of the ultimate re-sale value of this yacht. Either by building yourself or by 'managing' the build you can make substantial savings. A recent 'Spray' constructed by Fay marine was 'managed' by the owner. This yacht ultimately cost less than £60000 ($96000) but is insured for more than £120000 ($192000), showing that even with no labour input a saving of 50% is possible.


How easy will it be to find people to do the work if I manage it myself?

There are several materials that are popular for yacht-building. Traditional timber or plywood construction can be difficult and expensive as there are not many really skilled craftsmen left.

GRP is popular for mould produced production yachts but generally makes for an expensive hull. For the one off yacht GRP is fairly expensive and is a messy difficult process.

Steel shipbuilders are prolific and easy to find at the moment as the worlds fleets of commercial shipping shrinks. Steel has been a major product in the 20th century and there are many people experienced in it's use and in the last 30 years the tools needed to work with steel have become easy to obtain and use.


How long will it take to build?

Another difficult question to answer as everyone works at their own pace. Different designers quote vastly differing numbers of hours to build yachts of similar sizes. Often this is because of the difference between the designs. A hull with only one chine will be much quicker to construct than a multi chine version. The problem here is the looks of the vessel and the re-sale value. The single chine boat will usually be less pleasing to the eye, sail less well and sell for less.

Talking to home builders I have generally found that it takes three to four thousand working hours to put a 35 to 40ft yacht in the water. This means that a couple working two evenings a week and weekends could have a yacht afloat in about eighteen months. In practice it usually takes a little longer due to holidays etc.

This is a very rough guide. Only you know how hard and fast you will work. Go and talk to other builders and try to envisage how you will tackle the project.


Will it be as good as a yard built yacht?

There is absolutely no reason why the home builder can't produce a yacht that is equally as good as a production vessel. Many people find that by building or managing the building themselves they obtain a yacht that is exactly what they want. Many amateur builders pay more attention to the details than is the case with production yachts, producing high quality boats. A production yacht is usually built to a price, it will be aimed at a certain price bracket, meaning that often the gear aboard is kept to a lower standard than is possible. The home builders can choose for themselves where cost savings should be made and where high quality gear is wanted. A good example in these days of 'Marina hopping' is the anchor winch. Often quite large sheet winches are fitted to the yacht but the anchor winch is woefully inadequate. Fine if the yacht only spends it's life in marinas. Potentially a disaster if the unsuspecting owner is caught in an anchorage with a rising wind and expects the winch break the anchor out. This is just one example of where the owner/builder can fit the correct gear.


Must it be surveyed?

When a yacht is home built in the UK it doesn't have to have a survey. This will have to be checked in the country where you are building.

However, it may well be a good idea to have the yacht surveyed for three basic reasons; The first is your own peace of mind, a surveyor should be able to point out anything you may have missed.

Your insurance company will probably want the vessel to have a survey.

Finally, when you come to sell your yacht a prospective purchaser will be pleased to find that the vessel was surveyed during the building.

To save on the cost of surveys, some builders just have the hull surveyed when the hull  is complete but not fitted out. The surveyor, insurance company and potential purchaser will appreciate this as everything will be easy to examine and a survey at this stage should be inexpensive but well worth it in future dealings.


Where will I find information?

Boat building information is easily available. There are discussion pages on the web where questions can be posted. These will often be answered by some of the worlds leading designers who seem to look at these pages on a regular basis.

There are many books that cover all aspects of yacht construction, in all materials. These are normally available from your library. To find them take a look at one of the on line bookshops such as The Armchair Sailor who are in Newport RI USA.

If you have real problems with information about steel yacht building that are not answered then e-mail me your question. Please be frugal with the questions, I receive many, it may take me a few days to reply.


Can I increase the plate thickness?

I am constantly approached by builders who are thinking of increasing the thickness of the plate, either all over the hull or just below the water-line. The thought is usually to increase the thickness by 1mm from the 3 or 4mm plate specified by the designer, to make the yacht stronger.


This has two adverse affects. The first is that the yacht will be overweight, in some cases by so much that the amount of ballast has to be reduced. This is often coupled with the other effect which is that by thickening the plate the centre of mass of the yacht is raised, reducing the stability.


In an effort to overcome this some builders over ballast their yachts and raise the water-line, while others just accept that the yacht is tender.

On one 40 foot steel yacht, the builder decided to increase the deck thickness from 3 to 4mm as this would help to reduce the welding distortion. Good idea you may think. But hold on, that is an increase in weight of 33%, or in real terms about 500lb. and this weight is acting about 4ft. above the centre of mass. This can be represented as 4 x 500 = 2000ft.lbs or nearly a ton extra acting against the righting moment, which meant that the yacht needed extra ballast.


DON'T INCREASE THE PLATE THICKNESS. Steel yachts are incredibly strong! Most 30 to 40ft yachts could be built from thinner plate. The reasons why thicker metal is used, is the difficulty of welding thin plate, also to resist denting while alongside quay walls etc. and traditionally as an extra margin for corrosion, which has now been overcome with modern paint systems.


When designing the Fay 32 we specified 3mm rather than 1/8 inch plate. Only 3% thinner, but this represents a saving of 160lb overall. Which in real terms means that an extra 180 tins of food can be carried for those long passages.


Should I weld all the frames to the hull Plating?

If you weld the frames to the plating this will give the yacht a hungry horse look showing every rib. The frames usually only need welding to the hull skin where they meet the chine bars. Longitudinal stringers which are always stitch welded along the length of the hull, join the skin to the frames. Any horizontal lines on the hull don't offend the eye the way a vertical line does.


On the subject of frames, an enormous amount of time and effort can be saved, by pre-drilling the inboard edge of the frame pieces, with a 4 or 5mm hole every 6 inches or so. This can easily be done on a pillar drill before assembly. These holes can be used to screw the frame pieces onto plywood, which helps reduce distortion while welding them together. Later on when fitting the timber inside the hull it saves lots of awkward drilling.


How can I form the chines?

There are several methods of forming the chines. Round bar, T bar, butting plates together and flat bar on edge. They are all successful apart from the flat bar on edge which bends, twists and sags between frames and won't take up a nice curve. When fitting the chine bars to the frames, only join them with a tiny spot of weld until the hull is complete. Otherwise they tend to kink around the frame rather than gently curving.


Can I make my own deck fittings?

Most people building their own yacht are doing it because of finance, they want to save money. On a trip around almost any marina you can see otherwise perfect steel yachts that are spoilt because the builder tried to save too much on the deck fittings.


Making your own cleats, stanchion bases and guard-rails from mild steel will save lots of money. The problem is that many builders weld them onto the deck and then paint them. It is almost impossible to stop them getting chipped, rusting and looking nasty and then making rust streaks across the paintwork. Much better is to make all the parts from stainless steel which has fallen in price in recent years and is now very cost effective.


If you must use mild steel then weld the fittings onto separate bases of 6mm plate. The whole lot can then be sent for galvanizing, which is very inexpensive. When you come to weld them on, the galvanizing is ground off the edge of the plate, which is then welded onto the deck and the weld painted over. This produces long lasting, rust free deck fittings at minimal cost.


What is the best method to cut the steel?

There are lots of ways to cut steel. Nibblers, Angle grinders, Plasma cutting, and either oxy-propane or oxy-acetylene have all been used by home builders.

Nibblers are noisy, difficult to handle, and often won't handle cutting the thicker plate. Angle grinders are noisy, dusty, slow, and curves are difficult to cut with them.


Plasma cutting is very clean, but difficult to use and not very versatile.


Oxy-propane is very similar to oxy-acetylene, but you can't use an A.S.M.N. nozzle, ( described next ).

The finest all round method that I have found is Oxy-acetylene. It is very versatile. During your project you will use it to cut plate of all thicknesses, making both straight and curved cuts easily. It is quiet and fairly clean, only needing a small amount of cleaning after with an angle grinder. It will also be used to heat and bend bars etc. and for heating areas of plate if the hull needs 'fairing'.


The oxy-acetylene bottles can normally be hired from a local supplier. Have the largest you can as this saves time waiting when you run out and is usually cheaper in the long run. Buy a pair of gauges, some long hoses, (30 foot hoses saves moving the bottles around) and a cutting torch. Three or four 'pepper pot' type burners spanning the range will be adequate, and an A.S.M.N. ( acetylene sheet metal nozzle ) type burner will be needed.


It is stated that an A.S.M.N. nozzle is only for plate up to 3mm thick, in fact they will cut 6mm easily, 9mm reasonably, and I have cut 12mm with difficulty by turning the gas pressures up high.

These 'step' nozzles work by actually sitting on the plate, which makes using them easy. The edge of the plate is heated red hot, then the oxygen trigger is pressed which starts the burning process and the torch is pulled slowly towards you making the cut. I always use a guide made from a piece of flat bar, 6mm by 50mm by 300mm long, with an old screwdriver welded on as a handle. This is held next to the line to be cut and the nozzle ran along it.


Can I gas weld the steel?

Often people enquire if a yacht can be gas welded, to which the answer is no. This puts too much heat into the steel and would cause massive distortion and so can not be considered.


How should I weld it?

There are two methods which are Mig or Stick welding. Mig has the advantage of causing slightly less distortion and being easier to use. But is more expensive, carrying the wire feed unit around is difficult, and it can not be used in a draught as the gas is blown away. This means that it can not really be used outside.


Stick welding takes slightly more skill, but is less expensive. It is not so critical of conditions so it can be used outside, and with a long cable it is easy to reach all around and inside the yacht. A 180amp welder will be fine for all the welding except the heavy plate around the keel. The high amperage needed in this area will cause the welder to overheat and cut out after only a few inches of weld. It may be cost effective to hire a larger welding plant to tackle these areas.


Can the hull be used as the negative conductor, like a car?

Absolutely not!! Keeping the electrics out of the hull is a must, don't use the hull as the negative, the way it is done on a car. This causes massive electrolytic problems.

Also while talking of electrolysis you may want to use the modern plastic ball type sea-cocks, rather than the traditional bronze. This also helps keep galvanic corrosion down.

A tip from an electronic engineer friend is, if you have a 240 volt supply, fit electronic circuit breakers, but don't earth the hull. This is because if there is a fault in the marina your hull may provide an earth for a large part of the marina, with the resulting electrolysis.


Can I build a round bilge yacht?

Amateur construction of steel hulls is generally limited to either a hull with chines, or the radius chine method.

The simplest, and quickest is a design with one hard chine, although these tend to be less ascetically pleasing than any other type. The difficulty of construction increases with the number of chines, the only exception is around the bow, where a greater number of chines spreads the heavy compound curvature often found in this area.


Radius chine is a reasonable proposition for home construction. With this method enough plates to form the chine on both sides are all rolled to the required radius. Differing widths are cut from this pre-rolled plate and used along the length of the yacht to form the chine. This sometimes needs a little cutting and fairing amidships to make it lie correctly. The rest of the hull is built from flat plate, but due to the rounded chine has the appearance of being round bilge.

The only method that I have seen of producing a true round bilge yacht without rolling the plate, is to diagonally plate from keel to toe rail with narrow plates. This is a rather difficult method of construction, which usually needs much work to achieve a fair hull. One professional constructor in the UK produced very expensive high class yachts using this method but to achieve a fair hull a team of plasterers would cover the hull with filler prior to fairing it by sanding. Currently there are some designs being promoted for this type of construction and plans are being sold to amateur constructors. To date I have no knowledge of how successful these have been and time will tell how people fare with them.




Paul Fay and Fay Marine are dedicated to helping to further ease the passage with which sailors can achieve the goal of crossing oceans. I here freely offer, for individual or club use, this information. This may be printed and used free, for personal or club use. Permission to re-print in magazines other than club magazines or on other internet sites must be obtained from the author.


 İPaul Fay 1999