> ... I'd also like to
> use some kevlar inside the boat for impact resistance (per George Roberts'
> construction methods) and I should be able to use less kevlar (2-3 layers)
> rather than the 4-5 layers I'd probably put in a composite boat.

Remember the Kevlar is not good in compression and although the most concentrated forces on the inside of the boat are in tension, any bending in one direction must be balanced by some bending in the other. There will be a ring around any impact where the inside skin of cloth will be in compression. This stress will concentrate at the chine or sheerline. The Kevlar will not do much good at these concentrations. Make sure you have enough compression strength where you need it. This can be provided by carbon, glass or wood.