Sapele, Okoume, and Bruynzeel

Mosquito B.XVIs

We return to Paris and the grindstone. I've ordered a set of study plans, and all my spare time is spent thinking about the boat. There are many decisions to be made, and I don't want to hold things up by not having decided something, or needing to order something that we don't have and might be difficult to get. The first thing Tiernan will do is order the wood, so I start with that. 

The Cape Henry is built in epoxy coated plywood. When I asked Con what he thought about plywood boats, he shook his head disapprovingly and recommended GRP instead. Something like a Jeanneau Sun 2000. It's true that putting the words "wood" and "boat" together in the same sentence makes most boat owners wince. Lovely to look at from a distance, but the thought of actually owning one and being saddled with the continuous varnishing, painting, and otherwise battling against the inevitable decline into rot turns most people towards GRP. But when people think of wooden boats, they mean sawn planks of wood. This is the traditional boat building material that's been used since the dawn of time. And the one that scares people with images of rot. 

Plywood has been around for a long time. According to Wikipedia, an English engineer and naval architect named Samuel Bentham applied for several patents for machines used to produce wood veneers in 1797. In the applications he describes a process of glueing veneers together to produce the laminate now known as plywood. Constructing a wood laminate with the grain of subsequent layers in different directions results in a board that is more dimensionally stable, more resistant to cracking and less likely to warp than a sawn board. It can be thinner and lighter for the same strength. Aircraft engineers were among the first to exploit these advantages in extreme applications, culminating in the WWII de Havilland Mosquito. But airplanes don't spend their life submerged in water.

Corsaire n° 5 (collection Florence Herbulot)

In France there is a long history of plywood boats, and it is synonymous with the democratisation of sailing as a sport. Simple, affordable boats like the Corsaire, designed by J-J Herbulot for the Glenans in 1956, and the Muscadet and Armagnac (P Harlé, 1963 and 1966) led to the explosive growth of sailing as a hobby for the ordinary man. Many French navigators learned to sail on these boats. Many Muscadets have crossed oceans, and even taken part in Mini Transat races, and they still have loyal and passionate enthusiasts. But they were built before epoxy was used as an adhesive and coating, so they too have problems with rot.

The plywood-epoxy method of building boats was pioneered in the late 1960's by the Gougeon brothers in Michigan. They were the first to solve two historical problems in wooden boat construction. Firstly, using mechanical fasteners to join wood results in a weak point that must be compensated by using thicker, heavier pieces. And secondly, unprotected wood absorbs moisture and swells. Epoxy resins were beginning to be used as adhesives by pattern makers in the automotive industry at that time, and their moisture resistance was well known but they were difficult to work with and apply as a coating. In conjunction with chemists at the nearby Dow Chemical epoxy lab they were able to develop an epoxy that was suitable for boat construction. In 1970 they launched the first large wooden boat that was built without the use of fasteners and sealed from moisture. They soon started selling their resins to other boat builders, and the West System was born. Their book "The Gougeon Brothers on Boat Construction" is probably the most comprehensive book on the subject and is available as a free download here.

By the late 1970's, the new "lighter and faster" designs were proving their seaworthiness by challenging, and beating, the "heavier and slower" boats in ocean racing circles. In 1978 Mike Birch won the first Route du Rhum transatlantic race in a 37 foot composite trimaran, beating the 70 foot monohull Kriter V by 98 seconds after 23 days and 3,500 miles of racing. These days carbon fibre has replaced plywood-epoxy as the "composite" of choice in race boats.

RM 1060

The only modern-day boat yard that I'm aware of that builds a range of big cruising boats from plywood-epoxy is Fora Marine in La Rochelle. And their RM 1060 is my "lottery win" boat. There are many similarities between the RM 1060 and the Cape Henry. Light displacement, beamy, long waterline length, slippery underwater profile, shallow draught, twin head-sails, and plywood-epoxy construction. The RMs are very highly regarded in France, and that also reassures me.

Sapele and okoume seem to be the most commonly available types of marine plywood. They are both reasonably strong hardwoods, but sapele is heavier and stiffer whereas okoume is lighter and more flexible. Neither wood is very rot-resistant, but that's where the epoxy comes in.

I find the grain pattern of sapele to be more attractive, and the "stripeyness" could be used to good effect in the cabin. I'm thinking of leaving the galley units varnished, and the vertical orientation of the grain could add a feeling of height similar to the "short people should wear vertical stripes" thing. Tiernan considers this for a while but then reminds me that the grain in the bulkheads will be horizontal. We decide that we could veneer the galley units later if we want to. He goes ahead and orders 36 sheets of okoume. Building is about to start in earnest.

As for the longevity of our boat, only time will tell...