While on level Boat, you can use boats to attack the final helecopter. First know that all boat will blow up if you are near the ship when it explodes as the helecopter approaches. Thus you have to cheat and fly back to the boats on the other side of the island where the dock is tied to a boat. Seems that as long as you see the boat it won't self-destroy during the ship sinking. Now you can use the boat to fight the helecopter but lately I saved lots of boats in that area and tried to out run the helecopter but could not unless I already had a good lead on him.