> If we laid all of our epoxy/glass on the outside of the form the boat
> would be just as strong! But it wouldn't be waterproof. If we laid up all
> of the epoxy/glass on the inside and then removed the strips the boat
> would be just as strong! But it wouldn't be pretty. So we put half inside
> and half outside we get everything we need from this method. However,
> George using 1/8 strips and claiming is boat is just as strong is
> "TRUE". The fact that George claims his boats are actually
> stronger means that he has figured out another property of composites that
> the rest of us overlooked or felt wasn't important.

> The cedar strips are not a component of this composite. The composite is
> the glass/epoxy only, just as in a commercial fiberglass boat. Fiberglass
> boats are heavier for many reasons; gel coat, hardware (most homebuilders
> talk weight before rudders, foot pegs, rigging , etc., are installed.)and
> liability considerations.

Ian, you would be pretty much correct that the cedar strips add almost nothing -- if you're talking about a tensile load only. In other words, if you built a lay-up of only fiberglass and epoxy and submitted it to a tensile test (a tug-of-war with the panel) against a typical cedar-strip/glass/epoxy layup, the wood version would only be slightly stronger.

But a kayak never sees pure tensile loads. The loads we are most concerned with are bending loads. Let's say you had 2 different panels; one has 2 layers of cloth seperated them by 1/8" of air (let's assume we had a weightless spacer) and the other is 2 layers of cloth seperated by 1/4" of air. Now we subject them to a bending test where 2 ends of the panels are supported and we put a weight in the middle. Not to get cocky, but I'll bet you my engineering sheepskin that the 1/4" panel will be 4 times stronger than the 1/8" panel, even though both panels contain the exact same amount of fiberglass. It has to do with the moment of inertia of the panel.

The heavy stuff: The stress in the panel is inversely proportional to the moment of inertia. Max stress=(bending moment)*(1/2 panel thickness)/(moment of inertia) The moment of inertia is proportional to the square of the distance from the neutral axis of the body, which is the center of the lay-up. Moment of inertia=(area)*(distance from axis)^2. What this means is that if you double the distance between layers, the force quadruples. If you quadrupled the distance between panels (say we went from 1/8" spacing to 1/2"), the panel would actually be 16(four squared) times stronger. In bending.

George's 1/8" panels will see higher stresses than the typical 1/4" panel sees, under similar loads. This is just basic engineering. George's claim is that he can apply a stronger fiberglass and epoxy lay-up that will withstand these increased forces. And give a substantially lighter boat, to boot.

Dean