If you drop a steel bolt in a bucket of water, the bolt quickly sinks to the bottom. Then how can a steel ship float?

Azabu Explorers learned that it has to do with the density, or the mass per volume, of the ship (and its cargo) -the boat should be big enough for its weight to spread on the water. Also the gravity is pulling the boat down but the water is pushing the boat up.
And they built sturdy boats by tinfoil then challenged to fill the boat with many small blocks as they can without it sinking!