Basically if you wanted a round bottom boat you'd have to either cover the stringers and frames with foam then glass that or start with a molded skin from a female mold and add the stringers and frames to that. If you cover the stringers and frames with foam and glass both sides then you don't need the stringers and frames, the cored glass is plenty strong enough without them. To make a suitable female mold to get a single skin is a huge amount of work and can be quite expensive. If you were making a race boat where every once counts it might be worth it, otherwise it's a heck of a lot of work for very little gain, you might save 2 or 3 lbs. total in the weight of the boat.

Bill H.