Hi Tim,

Depends I think very much on the shape of the boat. If it's mostly rounded sections then a single skin hull will probably be fine with ribs or stringers, if though the shape has large flattish areas then a foam core will likely be better.

You very likely don't need both stringers and frames, one or the other will likely work fine. Usually ribs since you'll at least have gunwales to attach the deck to add longitudinal stiffness and also likely a keel.

Truthfully sounds like a fun project.

Btw, with decent fabric and epoxy and no gelcoat, even if the skin does flex some it really won't matter structurally much (though it can add drag), my SOF's which are basically single skin glass/epoxy flex a lot, matters little. The average person thinks of fiberglass as a thick rigid material, doesn't have to be.

Bill H.