: I'm looking for opinions concerning the structural strength of different
: thickness of strips...ie...3/16 versus 1/4 versus 5/16. I am not
: disregarding weight here, but I really don't see a big weight penalty
: using thicker strips. It certainly is easier to build with thinner strips.
: In the same grain what is the opinion of using multiple layers of
: epoxy/fiberglass for strength versus thicker strips. I would think there
: is a greater weight penalty using multiple layers of epoxy/fiberglass
: versus thicker strips. Possibly there is a happy compromise. At this point
: I'm more concerned with structural strength. I'll consider aspects of
: durability, toughness, puncture and scratch resistance
: later....UNLESS...it all turns out to be a melded combination. Just
: kicking a few things around. I figured some people would have their own
: opinions based on experience.

The reason the strip system works so well is because the finished hull is a composite of fiberglass and wood. Primarily a composite of this type doesn't derive its strength from its core material. It's all about what happens when the composite is put in a situation that causes bending. That is when the hull bends at the point of an impact. This may be hard to visualize but during this bending action the fibers on the outside of the hull are in compression and the fibers on the inside are in tension while the fibers in the middle of the wood are neutral. The way the composite achieves structural strength is because the fiberglass/epoxy is very strong in tension. So the glass on the inside of the boat actually gives it the most impact protection and strength. The farther apart the layers of glass are the more you take advantage of the strength of the fiberglass layer. By saying that, it makes sense that the thicker the core the stronger the boat because that gets the composites layers farther apart. The core can actually be made from foam and still achieve the desired overall strength if it is thick enough. That is most of the story for structural integrity but that's not to say you can't damage the outside of the hull by hitting something sharp so you still need a fairly thick lay-up on the outside too.

So you have it right. The thicker the wood the less glass you need on the inside. You still need the same amount on the outside to fight abrasion and keep the small hits from denting into the core. You can't really achieve the same type of resistance to bending when you get the core very thin even at the expense of more fiberglass. The thicker the core the heavier the boat but the thinner the core the heavier the boat too. I suppose knowing the tensional strength of the different fiberglass/epoxy lay-ups one could calculate the optimal thickness for the wood core. I haven't seen those calculations anywhere but I can see that there have been enough boats built to find out that if you build the core between 3/16 and a 1/4 you will not have any problems. Why take a risk.

--KT--