Maybe faintember had it right,
I've seen it at Myrtle Beach on more than a few occasions where a child will get too far out (riptide, whatever), and her uncle went out to save her, he ends up needing help, his brother jumps in to save them both, and someone else goes in to try and save them, and no one survived 🙁
Three person yacht, so Possibly two of them were out swimming while the third one was setting up dinner, they start to struggle and the third tries to save them and falls over board.
It would be more than creepy to get on a boat and find everything as if there was someone living on it (eg, computers running, dinner set out and waiting, lights on, nobody home)
Maybe they can figure out how long the boat had been empty using the food that was set out for dinner? 😕