A boat sinks at the dock due to heavy rains or a dead battery other times it can be a list of maintenance items that fail like a thru hull fitting or a water supply hose from a bait well. Boat designed with self bailing floors when experience more than normal heavy rains in South Florida and that can spell disaster for a small boat if the bilge pump is to small to keep up with the water coming into the hull in turns weights it down by there stern where the heavy motor is once it reaches that point it will sink.