The Setting: Imagine that cruise to Hawaii from "Cruise Ship," except gone horribly wrong. What happens if that boat goes down? There are many terrifying possibilities built in, including the sinking of the ship. But think about the depths of the ocean, and what happens once the cast reaches a seemingly uninhabited island.
The Premise: If the boat went down in the very first episode, they'd have to worry about sharks, other sea monsters, and whatever awaited them once they found land. It could be packed with creatures, or a savage tribe of native dwellers. We're having trouble imagining any survivors.