Plans Methods Materials Skills


"Doing it right the first time is far quicker and less expensive than having to do it again"

Many different building systems have been investigated, tried, and used for Farrier designs over the past 30 years, from basic hard chine ply construction to female molded production methods. There has also been a huge amount of feedback from hundreds of builders, both amateur and professional, on what really works, and what doesn't. It is important to take advantage of this huge knowledge and experience base, so as to avoid hundreds of hours of wasted time. The main methods include:

Once the most common way of building your own boat. The materials are readily available, well proven, and most builders are familiar with it. The disadvantage is the room taken by the stringers and frames inside, the additional labor required, the additional weight, the potential for rot problems, and lower resale value. Many who have not actually built a ply boat still believe that there is less or no fairing involved, but this is incorrect - the moment the exterior is fiberglass taped or sheaved, then one has a major fairing job. Early Trailertri designs used this method, but it has now been discarded by superior strip planking methods.

The old way - traditional ply construction with frames, stringers, and glass taped seams as used for the original Trailertri series - this 720 was being built in Brazil. A very successful construction system and one familiar to just about everyone, but it is slower, more complex and more expensive when compared to the latest building systems. Trailertri plans were taken off the market many years ago as plans for plywood construction no longer offered good value.

Cedar or foam stripping is simpler, faster, and gives more room inside, as the space hogging stringers and frames with all their crevices are left in the workshop where they belong. Vertical foam stripping is even faster, while foam is rot proof, provides more insulation, and a higher resale value.

Note how the folding strut mounting brackets were built in place at this stage. These needed an accurate frame setup, with permanent double beam bulkhead frames as shown, and restricted hull material to plywood. However, the development of the modular and patented Central Mounting Module System as first used for the F-9A made it easier to incorporate the folding system while allowing the use of other hull materials such as cedar or foam.

CYLINDER MOLDING: Similar to tortured ply, which was tried but discarded for the Trailertri 18 back in 1974. It is difficult to achieve consistent shapes, the process being unreliable, and the many additional stringers and bulkheads required to be fitted later take too long, more than eliminating any initial time savings, while reducing interior space.

CONSTANT CAMBER: This can be a very useful and quick method of building for boats with basic or limited hull shapes. However, more advanced hull shapes such as used in the F-Series® designs cannot be built this way. Modern strip planking systems have now overtaken this method, while offering many advantages, and are thus now generally favored and used by most professional boat builders.

ALUMINUM: Not practical for small multihulls, the minimum skin thickness being too heavy compared to other materials, while welds can be troublesome and fatigue prone. Only for very large multihulls, and even then it is not much in favor.

COLD MOLDED: An older labor intensive method, with literally thousands of veneer or ply strips to be cut. Now very much out of favor.

FOAM SANDWICH - Male mold method - A way of building and achieving light durable boats, and giving a superior end result to all of the above. However, the common method of laying the foam over a male mold can be awkward and much too labor intensive. This system was used for the prototype F-27, and achieved an excellent result, but the labor required discouraged its use for a number of years, wood strip planking being preferred. However, the latest vertical strip foam core method, as developed for Farrier designs in 1996 has now outdated all other methods of foam construction, and is the favored system.

HARD CHINE WITH COMPOSITE PANELS: Pre-made and pre-cut composite panels are now available for hard chine construction, and these are being used by some designers, while low cost and quick building are commonly claimed. However, only limited hull shapes are possible, and once experienced, it soon becomes obvious that such panels not a fast or a cheap way to build a boat. One range of such kit panel boats in Australia was even withdrawn from sale after many complaints that construction was taking much longer than the claims.

The problems include panels that are very expensive, plus many panels have pinholes requiring resin coating or filling. The extensive taping required uses up enormous amounts of time and resin, adding considerable weight compared to a clean round bilge hull. The tape also sits proud and is a lot of work to fair, particularly for inexperienced builders. The frequent claims that such hulls do not require fairing is simply untrue. If any exterior taping is required over the many join seams then one will have a lot of fairing to do - I've been there - done that. Kit panel hard chine hulls are also less attractive, with a reduced load carrying capacity, and a much lower resale value.

Building the hulls can actually be the easiest and quickest part of a boat, most time actually going into fitting internal bulkheads/panels, and then assembly and fitout. Most of the internal bulkheads are already fitted in vertical stripped hulls when removed from the form frames, whereas they have to be done later with many pre-made panel systems. This can be very awkward, and further increases building time.


The methods that years of practical experience have now shown to be the best choice are:

WOOD STRIP PLANKING: Actually a very old way of building a boat, but modern epoxy resins have now made it perhaps one of the quickest and easiest ways. Many fore and aft wood strips are laid side by side on temporary form frames/molds, edge glued, and these provide the fore and aft strength. A suitable unidirectional reinforcing fabric such as fiberglass, combined with epoxy resin, is then laminated vertically, across the strips, to provide the athwartships strength.

An F-9A float being strip planked - a much better system than sheet ply, but there are many strips to carefully fit and join

Strip planking gives a light and stiff hull with no need for complex internal stringers or framing. It is easy to fair, and strips can be from a number of different materials, western red cedar the most common, it being very light and durable.

A further more advanced stripping method was also developed very early on for Farrier designs, with the hull and deck being built as one, in two vertical halves, in female form frames. This offers many advantages, including the use of half frames for the temporary forms, which then merely need to be turned around to make the other side, halving the amount of form frames required.

The hull, cabin sides, roof, and most of the deck can then all be made at the same time, as fully integrated vertical halves, avoiding considerable additional framing later. Interior bulkheads and panels are then easily and accurately added before the hull halves are removed from the frames and the halves then joined down the center. This is exactly where any extra reinforcement should be, for stiffness, and abrasion resistance.

A wood stripped F-25 main hull, still in the female form frames, with interior glassed and the bulkheads
and interior panels fitted.
Fitting bulkheads is easy to do at this stage, and the supplied full size patterns for
many interior parts eliminates the need to clamber inside the hull later to measure and fit, a very awkward
and time consuming process.
The hull is also quite rigid when removed from form frames and thus does
not need an extensive support structure to hold in shape.

FORE AND AFT FOAM STRIP PLANKING: The weight of wood stripped boats however can be disappointing, and to improve this, fore and aft foam stripping was tried in the early nineties. The lighter and more durable foam is not stiff enough to lay fair on its own so the strips were preglassed on one side with a fore and aft unidirectional. A vertical unidirectional was then laid across the strips, to complete the laminate. However, it was time consuming to pre-glass and cut up the strips, while the finished stripped hull was difficult to fair, and it took a lot of fairing putty or extensive sanding to blend in all the little flats and any raised 'hard' fiberglass edges. Laminating vertical unidirectional on a multi-curved hull, particularly inside, also tends to be slow and tiresome.

Fore and aft foam stripping - lighter, and a good advance over wood stripping, but there are still all those
numerous strips to fit and glue. Number of form frames required is also higher, the F-36 shown here
actually having four more Form Frames than the larger F-41 which uses vertical foam strips

To improve matters, frame spacing was reduced, so that the foam strips did not need to be pre-glassed. This was better, and the F-36 was designed to be built this way with unglassed fore and aft foam strips. But the basic problem of all those long narrow strips that had to be made/joined, handled and fitted, whether foam or wood, remained, plus there were many more form frames to make.

There had to be a better way.......!

and there is.........

FOAM VERTICAL STRIP PLANKING.... the very latest procedure, and the next major step.

It came about from using foam fore and aft strips, which gets very tiresome, there being so many strips to cut, edge glue and fit. It was suddenly realized that much wider and shorter strips could be used simply by turning them around and running them vertically. The more ductile foam core makes such a vertical orientation possible, and the strips can be held in place and very fair by temporary fore and aft battens. The vertical foam strips (or panels in some areas) are considerably easier to handle and fit, and the female form frame mold system also makes it very simple to hold them in place, as access is easy from both sides. Not only were the hulls lighter, but they were fairer, with significantly fewer joins, easier to laminate, and much quicker to build.

Fore and aft planking requires multiple glue joins,
meaning much more work, weight, and expense
Far fewer joins with vertical strips,Multiple flats have to be sanded
while tight curves are easily heat formed - - - - - - - - - - - - -- - - - - - - - - -- - - out with fore and aft strips - -

But better still, one also does not have to buy thicker foam in order to allow for the extensive fairing required with fore and aft strips to take out all the little flats, as is recommended by some promoters of fore and aft stripping methods.

Henny van Oortmarssen's F-39 float being vertically foam stripped. The small pieces of wood are
used to screw/hold strips against battens, until screws can be fitted from behind - makes it easy to
plank hulls single-handed

The battens do take a little longer to setup, but no longer than say the first 10 to 15% of the numerous strips required for the more traditional fore and aft wood stripping. Fewer more widely spaced form frames can also be used. The relatively few battens are then just quickly laid in wherever they want to go, or as needed, and from then on the much fewer/wider vertical strips are considerably quicker and easier to apply.

An F-9A hull half having the vertical foam strips applied. In this case the foam is being held in
place by screws through the stringers from the outside. This eliminates the need to crawl inside
a hull framework and working blind as with the male molds traditionally used for 'one off' foam
core construction.

Hull strips can vary in width from around 8 to 12" (200 - 300mm) by around 6 - 7' (1.8 - 2.2m) long. Fore and aft strips will be 32' (10m) long by around 1 1/2 - 2" (40 - 50mm ) wide and will require over 800' of join line! Over four times as much edge fitting and gluing required in fact.

An F-41 outer hull half being built with vertical foam strips. The large foam deck and cabin side panels are also being initially held in place by temporary screws and ply pieces from inner side until join glue sets. Quick and easy. Screws are then added from back for laminating, the original screws being removed. There are more screws this way but overall it can work out faster and easier than just using screws from behind

There is actually around 3000 less lineal feet (915m) of glue join line required with a foam vertical stripped 41 footer, and every foot of these joins has to be carefully fitted and glued. It doesn't take much math to work out the considerable extra work and weight with over 1/2 mile (1 km) more of glue line to be done.

F-9A foamed hull, with the screws on the outside to hold foam in place being visible

An F-33 main hull, fully foamed, laminated, and with bulkheads starting to be fitted.

Once all foam is in place, the inside of the hull is laminated, using either epoxy or polyester/vinylester resins as desired (epoxy only with wood). Bulkheads are then made from full size patterns and fitted, which is very easy to do at this stage, eliminating difficult fitting later. Hull is then removed for exterior glassing once resin has cured. Form frames are then simply reversed, and battens re-positioned to build the other hull half.

Completed float half, with bulkheads being fitted. Black material is peel ply - color makes
it obvious, and impossible to forget and leave in place which could ruin one's day later.

F-33 main hull with all bulkheads now fitted and just prior to removing hull from form frames.

Advantages over the old male mold method of foam core construction include all the holding screws being on the outside for access (no awkward crawling inside a mold) and stiffening bulkheads are already there when hull is removed from the form frames. This makes the partly finished hull rigid and easier to handle, a major problem with the traditional foam system being the hard to handle ‘floppy’ hulls that are produced.

A completed F-39 float hull being lifted out of form frames

The vertical foam stripping system has now been used on many F-Series designs with excellent results, and has become the recommended, and designer's preferred method.

Dean Snow's F-9R ready for final laminate and finishing. Note how wide the vertical foam strips are

The final word has to be from a builder, and probably the best qualified is Australia's Dean Snow, from Geelong, Victoria, who has built three Farrier designs (F-9A, F-82R and F-9R), and is one of the few to have practical experience with both types of stripping. He used fore and aft wood stripping for the F-9A and then vertical foam stripping for the F-82R and F-9R. Dean considers vertical foam stripping to be much faster and says "A float half in wood stripping used to take days with all the fiddly strips, lots of messy glue, and edge pins. With foam it's a fast moving, no mess, low stress job (on both form frames and builder) - a foam float half ready to glass takes less than a day."

A fore and aft cedar strip planked F-25A - still a good way to build a boat,
particularly if you like wood, but it is slower and heavier


Vacuum bagging is a process of using a vacuum under a plastic film to apply pressure to the laminate while curing, to give a very high quality part. It is highly recommended for bulkheads, and interior panels, and is the lightest and best method of making such items. It can also give a finished, and fair surface to both sides of any particular part, and experienced builders can use it for the complete boat.

The plans give full details on how to do the double layer bagging system as used on the F-24, F-28 and F-31 where both laminates on each side of the foam core are bagged simultaneously. This is an aerospace technique, but is relatively simple to do once the principles are understood. Try it and you will be delighted with the results.

F-41 hull halves having been joined, with outer laminate of port hull inner side being vacuum bagged.


Infusion is now becoming more popular in general and I first used this back in 1991, with a view to replace the vacuum bagging system we were using at Corsair Marine. However the infusion process proved to be slower, compared to our bagging system, and the finished product was actually heavier, so we did not persevere with it. The heaviest F-31 ever built was resin infused in fact.

The main reason for the weight increase was the relatively open cell foams in use at that time, which is now being rectified by the foam manufacturers. There is still a weight increase, but much less significant.

The infusion time was also slower than the vacuum bagging techniques we had developed for the F-27, but the cleanliness, lower fume level, and fewer hands required to setup (can even be done single-handed) has definite advantages, particularly with items that have very little core (such as the beams) and the F-32 beams are currently being resin infused.

F-32 beam being infused

However, I still do not recommend infusion for 'one off' boats, as the learning curve is long, and one could lose a whole hull if not done right. Setting infusion up will also take much longer than just getting in there and laminating 'one off' hulls manually. Plus hulls that have been hand laminated well are likely to end up lighter.

But in series production, there can be significant time and emission advantages for a boat manufacturer, once set up. If more interested in the process, rather than getting the boat built in the quickest possible time, or the higher level of cleanliness appeals, then by all means give infusion a try - but be warned that it will take considerably longer, and there are some risks.

The only area where I would consider using infusion with a 'one off' boat would be flat panels bagged on a table, as it is a cleaner process, but this again will take longer to setup due to the learning curve.

Many however do not share by my caution on resin infusing, and some good arguments for infusing are on Henny van Oortmarssen's web site:

Building an F-39

Plans Methods Materials Skills

Return to Main Study Site