Originally posted by GunsForBucks:

From what I understand the boat will totally and suddenly stop when you get off it.

So maybe to be sure just jump in the water and swim to the ladder and log out then. That way when you log back in you should still be right by the ladder.

Exactly.

If you log out, the boat lowers its sails, but doesn't lose momentum.
So when you get disconnect and spawn somewhere in the ocean, try to recall the general direction you were sailing in and you should find your boat again a few clips outside of your render range

When you want to log out on a boat, always bring it to a full stop first, by jumping off and climbing back in.