First, recognize what you have. Are there stairs on the ship? Do you have some exercise equipment? Is there a track around the outside of the ship? Take a look around to see what's available. Even if it's just you in a room, you can still use your bodyweight to perform challenging circuits, including skipping, marching in place and jumping rope.
Think of this as an opportunity to change your routine and focus on the basics. Ask yourself which exercises you can modify to do in place, such as lunges. List all the moves you can think of and create a bodyweight circuit. After your circuit, hit the stairs for at least five minutes.