> The wood in a strip built boat does add significantly to the stength. It
> serves to keep the inner and outer layers of cloth seperated. By keeping
> the layers apart the load on the cloth is distributed over a larger area
> and the stress on the cloth is reduced. The core increases the mechanical
> advantage of the cloth for absorbing the load.

> In order to do this, the core does not need much strength parallel to the
> plane of the layers, it just needs good compression strength perpendicular
> to layers. This is why end-grain balsa makes a good core material even
> though it is very weak by itself.

Sorry Nick,

Re-read my post and realized it missed the point I was driving at.

From what I have read on kayak hull failures, most caused by rough surf landings and some by subsurface rocks, what seems to have failed is the cedar strips. These failures were caused by a force perpendicular to the layers. Several of the kayaks involved had no visible damage to the epoxy, some weren't even scuffed. In most cases the cedar strips actually broke, sometimes the epoxy simply delaminated from the strips. (I am betting that the strip actually broke parallel to the surface of the strip just below the area of resin saturation.)

What I was trying to get at was that this weakness in the strip is actually greater in a thicker strip because of the mechanical leaverage. (Much like trying to break a pencil with your thumbs close together as opposed to having them on further apart.) The fact that our epoxy layup can flex farther than the cedar strip makes the strip the weak component in the composite.

By using a 1/8 strip we would, in effect, be allowing the strip to flex more to the epoxy and we would be eliminating a large area that is suseptable to breaking parallel to the layup. I don't think this would be a problem with a hardwood because the hardwoods would be as rigid as the epoxy, but because the properties of epoxy and cedar are so different it is.

I think the lose of strength from the 1/4 strip to the 1/8 strip would be minimal and would be far out weighed by the increase in toughness. (The hull would not fail until closer to the structural limit of the epoxy.)

Hope this makes sense! Ian