I'm not sure about boats, but in RC airplane wings, laminating a vertical web of glass or carbon fiber between the foam strips develops the shear web, and allows sustained high-G, high speed turns. This would be a PAIN in a boat, but it's possible.

To accomplish the same thing, consider running stringers lengthwise of 1/4" spruce sticks (assuming you use 1/4" foam)or something, every inch or two. This would connect the two sides of the layup, and give you your torsional strength.

One more thing to consider is most foam's total lack of impact-resistance... your boat would dent badly on the bottom of the hull. Full size craft use vertical-grain balsa wood to combat this, but it soaks up a ton of epoxy, so you'd be losing the weight you gained on the foam... something to consider.

Nathan

> Structural members being bent develop tension stresses in one face and
> compression in the other face (tension in the face becoming mone convex);
> the material in between developes shear stresses (sliding forces between
> the faces). The styrofoam would not be capable of developing the shear
> stresses. The result would be two epoxy/glass layers in stead of one
> structural sandwich with a major reduction in strength..