What makes the ship float?
it is overall less dense than water, and so as a whole it displaces a volume of water whose weight is equal to the weight of the ship. when the weight of the displaced water and the ship are equal, the ship floats. note while the walls of the ship are metal (and much denser than water), most of the interior of the ship is air, so the average density of the ship is a lot less than that of the metal walls alone.. http://en.wikipedia.