An object floats if it is less dense than water. I'm assuming that an aircraft carrier can float because there are several rooms in it with air. What happens when the door on the upper most floor is opened? Does the air inside that room still contribute to the total average density of the ship? How exactly do you calculate the density of an aircraft carrier. Where do you draw the line when calculating its volume? If a door is open does the room to that door count towards the ship's volume irregardless of whether or not the door is open or not?