I had always thought that things float when they displace an amount of water that weighs more than them. Bur obviously this is wrong because I recently read about "Floating a Battleship in a Bathtub" were the author of a physics book said that as long as there's enough water to fit between the boat and the tub, even a millimeter thick, the boat will float. So what determines if it can float or not? He mentioned pressure on the boat. Also, what is hydrostatic pressure and how does it have to do with this? Thanks.