I found a bug where if you time a harpoon throw precisely you can trick the game and get outside the ship, but for some reason you still follow it.
Had same bug happen to me, the player still follows the boat because it is attached to it as a child object, basically what it means is that player has it's own coordinates and boat is zero in them, so player copies movements of boat and can add it's own movements (basically boat speed is x and it is constant for player, and player speed is y, and they add up). Hope this clears it up.