General Knowledge
Why can a small boat float when the steel it is made of sinks?
- The hull shape displaces far more water than the steel
- Air is trapped in the metal
- Boats are made of light steel
The answer is The hull shape displaces far more water than the steel. Shape, not material - it displaces its own weight in water.
Because floating is about the whole object, not what it is made of. An object sinks until it has pushed aside a weight of water equal to its own weight, and a hull encloses a large volume of air - so the boat as a whole is less dense than water even though every part of its skin is denser. Crush the same steel into a solid block and it sinks immediately.
That is why a ship's size is quoted in displacement, which is literally the weight of water it shoves out of the way. It also explains the load line painted on a hull: add cargo and the ship settles deeper until it has displaced enough extra water to match, and the marks show how deep is safe in different waters, since warm and fresh water are less dense and give less lift.
Losing the enclosed volume is how ships sink. A hole lets water replace air, the average density rises past that of water, and there is no partial floating - which is why watertight compartments exist and why the Titanic's failing was that its bulkheads did not reach high enough, so water spilled from one into the next.