Okay everybody, This might sound a little heretical, I have a theory that questions the very basis of our faith in wood/composite small boat construction but here goes:

Is wood sandwiched between two layers of glass really the optimal method of construction for a mostly convex craft?

Before you answer this, ponder these points:

-Most tests of this type of construction are done with flat panels (usually 12" x 12"). There are very few places on the average woodstrip kayak that are that flat, except maybe the bottom and some areas near the bow and stern.

-These panels work because the fiberglass on the back face is put in tension when a point load is directed at the front face.

-On a convex surface, there has to be a great deal of compressive failure (and buckling) in the core and outer face before the inner surface sees much tensile stress.

-Think about an egg. An eggshell's shape provides it with one of the greatest compressive strength-to-weight ratios of any object known. An egg is not made with sandwich construction; it has one structural layer.

-Think of an egg with three layers: its original shell; inside that, a lightweight sandwich layer; and inside that, a layer that is very strong in tension (same tensile strength as the outside shell's compressive strength).

If you put a big point load on the egg, the outer shell and sandwich layer will fail long before the inner layer. Now, wouldn't the inner layer have been more useful as an extra layer on the outside?

Here's a marine surveyor, David Pascoe, and what he has to say about cored hulls on larger boats: http://www.yachtsurvey.com/HiTech.htm Obviously, we get a bit better adhesion between epoxied fiberglass and our softwood cores than the foam cores shown in the "horror photos", but... Look at the diagram showing the effects of stress and bending on cored panels.

Here's another article by Pascoe: http://www.yachtsurvey.com/core_materials.htm In it, he says, "The other problem with coring a bottom has to do with the inability to calculate and estimate stress on complex shapes. It's easy enough to calculate stress on a flat panel, but change the contours of that panel, introduce the factors imposed by human error, and any benefit that might have been obtained by coring the bottom is long lost."

I'm not trying to knock the accepted method of construction. Heck, I love wooden boats; I just got to thinking last night and wondering....

I won't mind if anyone disproves my theory; I'll then be able to sleep better at night! :)

Shawn

P.S. I know what Nick's book says, and I know what Moore's book says. I just can't reconcile that information with my mind's eye view of a convex curved surface.