Ships float in water,although they are made from iron and steel which are materials denser than water. This is due to the fact that the ship is an 'open' object,not a solid object.It resembles a large hollow object whose outer surfaces are coated with iron and steel.
The volume enclosed by the bottom and sides of the ship is large.Thus the weight of water displaced is large.
The ship sinks to s level such that the upthrust is equal to the total weight of the ship.
The size of the ship is often listed as '10,000 tonnes displacement', for example,since it's weight is equal to the weight of the water displaced.Upthrust is the upward acting force while weight is the downward acting force.