As single-handed racers of substantial length, these boats do indeed have voids filled with foam for added buoyancy. Being sail boats their keels can way as much as the boat itself. Hence the self-righting ability. Most skippers when they do go below do close the hatches during bad weather. This would prevent some water from coming in and swamping the boat. Evidently, as part of the training on the boat he did have it capsized with a crane to experience what happens. Never been that kind of situation but similar ones at the hands of others.