What boat should I build?

Part 2 - choosing the material and the boat plan to fit

In part one we determined my builder profile (I am playing at being the first time builder to illustrate the method):

• A sailor at heart
• Likes speed
• Program is day sailing and fast weekend cruises to the islands (Ile de Yeu, Belle Ile...)

And a likely candidate was found for ply on frame - the fast weekender 8.5 metre cat "Punch" by Philippe Harlé. But lets look at some other options both from that time and now. The size is right for the program so we will stick to boats around 28' or 8.5 metres. Back in the early '80s Sylvestre Langevin had drawn a 26-28' ply or aluminium cat (Catapult) that was either built from plans (ply version) or delivered as two aluminium hulls ready to finish. Not having the experience welding aluminium I would have chosen the second option. A cold molded cedar and mahogany trimaran by Newick also fits the bill. Today in 2006 the Farrier F-82 would also be a choice, even for a first time builder. The method developped by Ian Farrier for foam cored composite construction of his trimarans is about as easy as it gets.

Ply on frame

This used to be the method of choice for the amateur builder. It requires some woodworking experience, but most of the molds used to define the shape stay in the boat as frames. That isn't a problem on a monohull but the dead weight of extra wood is not very good for multicoque performance. The finished boat can be coated in epoxy which will make it last much longer than boats built in the 50's and 60's where water trapped by the frames often led to rot. A protective layer of glass is also used on the outside nowadays to prevent abrasion from wearing through to the first veneer of the ply. Always use marine grade ply when building ply on frame.

Aluminium

This material is no longer used for building small multihulls. It has some qualities: it material supports beaching and does not need paint on the outside above the waterline. Good material for a boat that will be left on a mooring, say on a tidal mud flat and that will be used where contact with the beach or oyster banks are a probability.

Cold molded wood

The first material in the list that permits building hull shapes that are more complex than flat developable cone shaped surfaces. Requires a male mold that will be thrown away after the boat is complete. Requires some woodworking experience and a helper. Two people can mold a hull in a very short period of time when they have aquired the experience. Two types of wood are used today: solid wood veneers or thin marine ply (3 or 4 mm for a boat our size). Strips of veneer or ply are attached to the mold with temporary staples. In the case of solid wood a layer of hard wood, usually mahogany, followed by several layers of lighter wood such as red cedar, then finished by a layer of hard wood and glass cloth on the outside are applied. Each layer of wood is epoxy glued to the preceding layer at a different angle. The usual means of attaching the veneers while the epoxy sets is with stainles steel staples. These are removed before sanding and applying the next layer (often the staples are shot through plastic shipping case straps which make pulling them out easier). If a staple breaks or is forgotten there is no real issue because it will not rust and rot the wood around it. In transatlantic racers of the 70's a layer of carbon fibre was often applied before the last layer of wood. This made very light and incredibly rigid boats, Walter Green being one of the most respected designers/builders at that time using this technique. Once you get the hang of it easy method for a first time builder. Gougeon Brothers on Boat Construction: Wood and West System Materials is an excellent book describing this technique, other books can be found here. Plans for this type of trimaran can be found in Dick Newicks catalogue.

Foam core epoxy glass composite

As above, complex hull shapes are possible using this technique. Requires a female mold (or male mold depending on designer) that will be thrown away when the boat is complete. Vertical strips of foam core are attached to the mold then covered with directional glass, aramide or carbon fibre set in epoxy resin. Alternative method: horizontal bead and cove foam strips are applied to a mold to achieve the same result - two structural skins separated by a foam core. See the articles published in the building section to get an idea of this method in action. Plan using this method - Farrier F-82.

Other methods

For the Punch catamaran we could use stitch and glue ply/epoxy/glass composite. The frames are the mold and all of the deadwood stringers are eliminated. Result - a lighter, stronger hull that gets its strength from directional glass fibre. A layer of aramide on the bottom (there are two types of aramide - trade name Kevlar - one is structurel and the other anti-abrasion) will make it practically bullet proof and carbon fibre can be used to reinforce stratigic places like beam seatings and chainplates. The best place to learn about this method is here. Strip planked red cedar covered with glass is also used in multihull constriction as are various other light weight core materiels. Some techniques and materiels are quite adapted for amateur construction but there are no stock plans available for them...

Most amateur built multihulls are lighter and stronger than a factory built polyester/fibreglass equivalent. This is the one category of boat where it is possible to build something that will outperform the cookie cutter variety! If you are careful you can also attain showboat hull beauty.

Choices, choices...

And the winner is... The Punch 8.50 but built in stitch and glue ply/epoxy/glass composite. I am familiar with wood and ply so it is logical for this hypothetical first build that I stick to materials that I know best. But by converting the plans (with help from a designer) to stich and glue the result will go together faster, be lighter, stronger and cheaper. I am updating a 1980's design to 2000 materials and techniques. The design has proven itself as a fast comfortable boat and the size is just right for a quick easy build and to fit the program we set in part one.

Runner up: the Farrier F82 trimaran carbon fibre variety. This second choice is a what the heck(!), I'm building a boat, lets learn something new! And try for a light, high performance weekend cruiser that we can also put on the starting line of local regattas. Foam core fibre epoxy composite is the high-tech choice for amateur construction.

Next time we will go into a deeper analysis of the first time build.

Tony Grant [kiwi]