ORIGINAL: Ron Olson
Now that he mentioned it, I'm far from knowing a lot about combat ships but what little that I do know is that the hulls have to be made from balsa, not fiberglass.. They have a test where they drop a rod to see if they can puncture the hull as a test.
Frames can be whatever the builder wants, including fiberglass, plywood - I've seen or heard of them being made of polycarbonate (plastic) or aluminum, even. Fiberglass hulls generally start out complete, with "windows" cut out to simulate a traditional ribbed construction, with balsa as a skin on the outside. Most, if not all clubs have rules regarding how much area or percentage of the length at the waterline must be penetrable. Some clubs use a drop test, others don't.
JM