How does a steel ship float on water if metal is heavier than water?

The easiest way to understand the science involved is to float a metal bowl.

While the metal itself is heavier than water and would normally sink like a stone, the shape spreads the weight over a large area.

So, while the metal’s weight causes the bowl to sink somewhat, the bowl’s rim is high enough that the bowl will not be totally engulfed by the water. A ship is not unlike a large bowl.

The surface area is much larger than you’d expect if you only see the top portion sitting above the water.