Howdy hey there.
Sorry for the late reply.
In order to pass the pirate ship, you need to save a maid in the fort area who is being assaulted. Save her, go up and find a demon in the fort. He will tell you about a special storage area. Steal the key to said storage area from the fort commander's room, go out and around the fort to the center back and the head down. Interact with what you find there and then continue with the pirate invasion as normal.