SuperTigre --

another thing to know is that the rules define what it means to sink... and although the rules say that you may not prevent your boat from being able to sink, they also say that a is considered to have sunk if, for instance, it's decks are completely awash. So according to the rules, the boat can sink without you having to search for a completely submerged hulk.

also, people do sometimes build floating buoys into their ships (for instance you could have the suerstructure highly boyant and attach it to the hull with heavy chord) to make recovery easier if the hull is entirely submerged -- in addition to waterproofing the equipment compartment as Umi said.