[Bungleau]

AFAIR, the west gate doesn't open until you buy the ship. Once you've bought it, though, you don't have to use it.

I've found swimming to be faster, primarily because the boat has that annoying habit of speeding up and slowing down, like wave action might do. When swimming, that doesn't happen.

Also, it's much easier to stop and check the bottom when some scout senses a crab or shark nearby if you're swimming. If you're in the boat, you have to stop, get out, look around, slay sea beastie, search for shell, and get back in. Quite the pain, IMHO...