Tyro
Steampunker
As it is I've had ocean chests spawn in places which are visible on the map, but impossible (AFAICT anyway) to get to. It's also a potential problem if you've dug a quarantine tunnel just above the Cavern layer (since altar smashing makes evil in the Cavern layer specifically) to prevent corruption of the Underground and Surface - you can't bring the tunnel to the true edge of the map, which makes protecting oceans a pain 