What happened to that Typhoon? They should have multiple failsafes. I can only think that there was a massive ( Engel subs have a pressure switch that will detect a drop in pressure inside the hull from a leak and automatically bring the sub to the surface) leak into the dry hull. Can't think how though if some basic tests were done first. I hate to think what a flooded Typhoon would weigh, but I suspect your going to have to use steel cable rather than string to haul it out!