and to add to truthinbeer:
Even the biggest ship needs no reason to go down ..
IT can go down, if it just wants to. .. after all, Uncle Davy Jones Locker is waiting to snatch anything that floats !!
Seriously, having worked with a company doing salvage, I believe truthinbeer's reply is more accurate .. add to it an engine failure .. there is only one way the boat can go - DOWN !