Plywood and Lumber for Boat-Building

Thoughts on suitable wooden boat construction materials, and where to get them. May 23, 2007

I am a cabinet shop, not a boat builder, but a valued customer has come to me for the rod compartments, battery boxes, seat pedestals and things, and wants them put in an aluminum boat. I know a little about marine grade plywood. I have always heard the only difference is that it has no voids in it, but years ago when plywood boats where common, some manufacturers would cut costs by using marine grade for the long length required for the sides and bottom, then using BC for the transom. The first place to rot was the BC grade transom, but also the sides and bottom where meeting the BC grade transom. I was thinking the BC had voids that held water. Where can I get the longest and widest marine grade plywood? I have tried everywhere in Nashville, TN with no luck.

Forum Responses
(Cabinetmaking Forum)
From contributor R:
Marine grade ply differs in the glue used; the ply grades and defect specs are the same. You can have any veneer you want laid up to marine specs if you're willing to pay.

From contributor J: sells a fair amount of ply for boatbuilding purposes. Might be worth giving them a call. If they don't have it, they should know where to get it.

From contributor P:
A friend of mine ordered some plywood from for his houseboat. He was making some sort of rib or something and wrapped the thing in fiberglass.

From contributor W:
You may want to consider white oak. White oak has been used for centuries by boat builders because it is almost waterproof naturally. Unlike red oak, white oak's cell structure inhibits the absorption of water.

It will look much better than plywood and will last much longer. Almost all of the old sailing ships had major components made from white oak and live oak knees harvested from the North Carolina, South Carolina and Georgia coastline.

Check out a book called "The Elements of Boat Strength" for answers on what to use. That's where I got this information.

From contributor S:
You used to be able to get marine grade plywood in huge sheets (like 7' x 20' and bigger) and you still may be able to. I don't really know a link or name for you, but there was a time and place in northern Indiana (30+ years ago?). I remember as a kid a neighbor rebuilding a boat with huge pieces for the hull and solid stock for the transom. I think the stuff probably came from someplace that builds/repairs boats rather than your typical lumberyard. If you can't find what you need, maybe opt for the epoxy resin coating.

From Professor Gene Wengert:
Marine grade plywood is B and better veneers with no voids of any size, plus an exterior adhesive (just like we use in CD-X plywood). It does not have any natural or man-made decay resistance unless the species used has some. White oak *heartwood* is a good or better choice indeed.

From the original questioner:
So you think white oak would be the way to go? I was thinking of planing it down to 1/2'' thick when gluing up to get wider stock. Titebond3 or a construction adhesive? I know people claim F26 and other construction adhesives are stronger than the materials you use them on, but I have seen them dry out, crack, and turn to nothing. Just exterior latex primer? Then paint and carper over it? I remember seeing that 7x20'' plywood. It was 200 bucks a sheet 30 back, but looked like crazy a few years ago and could not find it. My uncle said treat it with Copertox, but I have found nothing on the web about it.

From contributor I:
Boats are a very different environment. Any unprotected wood is not a long term solution for anything except cabin joinery. Wrap all exterior wood in glass and epoxy with something like West System from West Marine. Also, check out the Gudgeon Brothers (forgive my spelling). They literally wrote the book on marine epoxy. The only other viable option is teak. It requires annual maintenance but looks great when cared for.