Making the floats absolutely bullet proof would require you make them too heavy to be practical. What you really want is the tradeoff that will give you the most possible strength above some threshold with the weight as low as possible. You will be supporting much more weight than a white water kayak and it will be traveling much faster. Hitting a rock with a 500# plane moving at 20 mph is a much different senario than 250# hitting at 10 mph. The kinetic energy is 8 times greater. Therefore the strength requirements are at least 8 times greater. And the consequences of a failure aregreater with the ultralight. There must be data tables for the strength requirements of airplane floats somewhere. You should get some advice from the airplane world, I wouldn't trust us kayak builders.

For what it is worth, a typical glass composite sea kayak has about 4 layers of glass. A heavy-duty expedition boat may have more.

: I have a question regarding the number of layers used in an all composite sea
: kayak designed for rough service. First off let me say that Im not
: building a kayak, but rather a set of 12' floats for my ultralight
: airplane. I have the plug built and Im almost done with the last half of
: the mold. Ill be using E Glass for the outer layers and Kevlar for the
: inner layers. The last inner layer will also encapulate either honeycomb
: or foam core material to act as a stiffener. One the layup is done Ill be
: vacuum bagging the whole thing. Question is...If you were to build a
: bullet proof white water kayak using these methods, how many layers of
: glass would you use and what weight...and how many layers of kevlar would
: you use and what weight. Weight is very critical here. The structure needs
: to be as light and as strong as possible. I would like each finished 12'
: float to weigh no more than 20 lbs. I think this is possible by using a
: glass/kevlar hybrid method. Thanks for you input....Ross