by Satire
Your analysis is pretty true: there's no reason to end in uncharted waters most of the game.That said, I think your solution is pretty punishing: if you're blown off-course and can't complete your intended actions that's a punch to the gut equivalent to "lose a turn." In a game with so few turns I think that's too much.
Instead, what about:
While in uncharted waters, taking a sail action longer than three empty hexes necessitates drawing an Uncharted Waters card on the third empty hex you pass.
That would mean that routes between islands would get populated with more interesting features between them, and would give atolls more value as a place to "reset" your empty-hex count.