> I am very close to buying the materials to build 2 CLC Patuxent 17.5s. I
> am still toying with the idea of using 3mm plywood all around to save some
> weight. We plan to use these kayaks for flat water racing and day
> tripping. Using 3mm plywood, will these kayaks be too fragile and
> flexiable for my intended uses? Oh...I do plan to fiberglass the hull and
> probably the cockpit.

> Thanks again,

> Steve

George Roberts builds with 1/8th inch thick strips, which is awful close to 3mm in thickness. He uses multiple layers of lightweight (approx. 2 ounce, I believe) glass cloth to build up strength while keeping down the weight. For example, instead of a single layer of 4 ounce cloth, substitute two layers of 2 ounce cloth. And for 6 ounce cloth, use 3 layers of 2 ounce cloth. The amount of resin is the same either way: figure it by weight For each yard you cover you use either 4 or 6 ounces of mixed epoxy, depending on the weight of the fabric. George has posted the order he does his layups a few times. You might want to take a look at them. If you can't find that info in the archives you might e-mail him and ask his advice, or maybe prevail on him to post it once again.

The shape of the deck is also going to affect how flexible the boat is. If the boat seems too flexible when you use 3 mm ply there are a lot of ways you can make it stiffer. Basically you just need to add some stiffeners. These would be pieces of wood, something like a furring strip laid down the centerline of the interior of the boat. Bond that to the hull with some epoxy and the hull will be much stiffer. If you don't want a piec of lumber in the center area, a similar effect can be obtained by using wood strips in the chine areas to left and right. Cut them to fit over the resin fillet and glue them in. The bigger the wood the stiffer the boat. Even a thin piece of wood can add to the stiffness. If you glass over the wood you get even greater stiffness. If you want you can make a tube from newspaper, wrap that with a couple layers of glass and apply resin to make a (mostly) fiberglass tube that you can use for adding stiffness. For cross bracing you can cut, and glue in, deck braces, frames or bulkheads.

Don't rush to make the boat stiffer, though. Even if it is a flexible as an inflatable with a slow leak, you may find that this is a desirable attribute. Baidarkas and many skin/frame kayaks are designed to flex so they move easily with the waves, so you don't fight them. A 3mm boat may emulate that characteristic better than one built from 4mm. Try paddling it for a while. If you like the effect, pat your self on the back. If you don't, glue in some stiffeners.

Best of luck with your project.

Paul Jacobson