Several years ago, a friend and I tried to sink a 25' sailboat hull. Dang thing would not go down. Friend then climbed aboard the now sticking up straight bow, reached in the blown out bow, (we blew it open with a shotgun), (no need to ask but, yes, alcohol was involved), and pulled a bunch of foam and a couple of pfds out. Not a whole bunch but enough to cause it to not sink. Doesn't take much closed cell foam to float a boat.