Floating and sinking

Two forces act on every body which is submerged wholly or partially in water: the gravitational force which is directed vertically downwards and the buoyant force which is directed in the opposite direction, namely vertically upwards.

Floating

If a body has a lower density than the liquid it is submerged into, it will float on the liquid's surface. Only a part of the body's volume is submerged in the liquid.

But ships consist of iron and the iron's density is much higher than the density of water. Nevertheless they can float, because they also have a great volume and therefore displace a lot of water.

At floating, the buoyant force is as great as the gravitational force of the floating body and as great as the gravitational force of the displaced water.