I have played the game again (I couldn't forget it) and I have finished the game! I wouldn't think that the end would be so near.
Now I get the importance of lowering the sails. In my first play, I couldn't understand when a storm started. I thought it was night. Maybe there could be more "windy" particle effects when a storm starts.
I would really love to play an endless version of this game with more upgrades. When you have sextant in the early-game and you lower your sails, you can get all the possible upgrades before the finish (I think maybe when there isn't 3 upgrades available, it won't show the upgrade UI anymore). The upgrades and the mechanics of the game is really satisfying to my liking. It could be adapted to a longer gameplay.
If the git repository of this project is public, I would like to have a look at it and contribute to it.