: Ok I am thinking of how to build a new yak. Here is one of my probblems, a
: flat piece of 1/8 inch ply is to flexible. I am hoping that by making a
: tri-planed hull it will help make the hull a bit stiffer. Now how would
: you go about making this hull even stiffer? Add a second layer of ply or
: lay in carbon fiber, or is there a method that I am not seeing right away?

The quickest/easiest way for stiffness is thickness. Using a thick plywood on the bottom would probably lighter and stiffer than adding more fabric of any kind. You could try laminating a strip of wood down the inside centerline of the bottom as a keelson, or some cross ribs. Again, creating some 3 dimensionality adds a lot of stiffness so just getting some curvature into the bottom should help.