You may find out on the last level that when you fire your cannons at the Kraken you run out and there is still some health left on the Kraken. Well, to your right, there are some stairs. Go up the stairs and press O where the skull and cross bones are. It will swing a net of rum above the kraken. Get the kraken to appear up at the boat again and fire your gun at net of rum by presing down. The rum will explode and the kraken will die. Well done! You have completed the game but... as i found it will only say 87% complete (still havent found out why).