Why a coin sinks while a ship floats?

Ultraoversimplifying it, the coin is solid metal all the way through and weighs more than its volume of water, the ship has a large space filled with air inside it resulting in the weight of the ship and cargo being less than the weight of the volume of water it occupies.

This is called buoyancy: the coin has negative buoyancy and sinks, the ship has positive buoyancy and floats.