...Let's try and break this down. [ Says the guy who didn't just put himself in a position where he had to WIN! But hey, they were both stumped. ] To be honest, I don't think this has to do with the boat part, since we don't get any more details apart from there are passengers on it.

[ He assumes the thinking position: finger under the chin. ]

So the answer has something to do with the people it mentioned, and how there's not a single person even though nothing happened. Hm.

[ WOW HONESTLY GHOSTS WAS A GOOD GUESS. And if Della would like to win, the answer is, appropriately for the running gag, Because they're all married. ]