Here is my video playthrough of the final part of the game, with all the achievements, including this one.
1. This is after you resurface between the ice, make your way across a lot of surface, and melt your way through a cave section.
2. You'll arrive at your boat. Fix it up.
3. Get the engine hot.
4. Raise the sails, and the boat will come off the land.
5. My boat pushed an iceberg for a while, eventually it went away, and the achievement was mine.