Question

how does ships float even when metal sinks in water?

Answer 1

The situation can be understood by taking an iron nail sinks while the ships made of iron floats that all depends on density and shape. Ships are designed to displace more water so that the can get more buoyancy force to retain on water surface while and iron nail is not such designed. Further

Whether a body will float or sink depends on the density of the body. Density of a body is the mass divided by the volume of the body.

Density of an iron pin is more than water so it sinks. The density of a ship is mass of the ship divided by the volume of the ship. Although the ship is made of iron, the volume of the ship is so huge that the density becomes less than the density of water. The reason being, ship is not a mass of solid iron. There is lots of empty spaces and other less dense substances within the volume of the ship.