Further to the flotation query -

At the first UK 'Nationals' I was unfortunate enough to hit a submerged object hard enough to literally rip the port dagger and case out of the bottom of my Stealth. It is a tribute to JohnPs' building/design and the F16 rules on flotation that I was able to sail the (submerged) boat back to the beach - from about a mile out - in lumpy conditions and 12-17 knot winds.

It's just commonsense to have a minimum buoyancy requirement for a boat design.