Unless wataru is not on the Ship, starving the crew out is impossible. Remember they can buy food that the ship is selling (Unsure about the buy food thing as i can't remember exactly if he can buy food from the ship) (assuming they are on Wataru's biggest ship) and he has Platinum coins now 313 of them.
Yes, I'm aware he can buy food on the ferry, probably on the cruise ship as well. The keyword is
buy though - eventually he's going to run out of money and if the ship is properly immobilized (like the collapsed cave idea), they're not digging their way out of there for the remainder of their lifespan. Especially since the powers that wanted them gone could post a perpetual "immobilizing force" around them and keep it that way. My point is, it's expensive but one ship can be dealt with, even if it's utterly indestructible.
