Added 11 hours 42 minutes later
I think this is how it works. The hero picks up the track from the last texture he walked on. The hero doesn't walk on water; he gets on a ship. That's why the track doesn't change. You could apply a water sound to any texture and add a few squares of that texture in front of the boarding point, and it would switch to water music. But you could also cover the entire map with that texture, not just in front of the ship. I looked at the ship file, but I couldn't add a water track to it.