> Stress concentrations tend to happen where there is a sudden change in
> stiffness. This can happen with something that is stiff in the area of the
> load, but is less stiff elsewhere, or if it is flexible at the load point
> and stiffer elsewhere.

> A friend of mine is very successfully making flexible Kevlar composite
> boats, but he had some failures early on at the deck-hull joint where he
> taped them together. The flex of the boat was concentrating the stresses
> at the stiffer joint and causing eventual failures. By changing his joint
> bonding procedure to make it more flexible (more closely matching the rest
> of the boat) he fixed the problem.

> I think a flexible boat can be built very ruggedly, but the engineering to
> get the whole system correct tends to be more complex. For example flexing
> introduces the possibility of fatigue, which epoxy and fiberglass don't
> tolerate well. The Aleut built extremely flexible boats and we still don't
> why they did everything they did, but they were working with wood which is
> very fatigue resistant.

The wikings did also build very flexibel boats, They did not like stiff joints. Most of the old scandinavian klink boats are rather flexibel designs

The flexibel joints together with thin boards (wedge splited) made the boats very light to