Slow Build Eldritch Horror

[aimlessPolymath]

As a motivator for staying on the ship, "the ship seems intact and you might be able to literally have a second ship" might be a fine motivator on its own- ships are pricey.

I'm generally against big overt "this is dangerous" signals- Scripten mentioned gaslighting, and as a player I can't understate how scary it is to have the DM grin at you as they say "That's odd... You thought that door was closed all the way, but it's cracked open. Huh." Mysteries are scary. Having the DM out-and-out tell the players that something spooky is going on, but a) not knowing what it is exactly, and b) not being able to communicate the spookiness to the character is powerful.

Also- a lot of fear goes away when a combat drags on; consider having monsters that retreat when wounded or losing, and also static hazards that players think their way through.