Why do iron ships float in water?

[Himal kharel]

If you drop an iron nail into water it sinks. But a ship made up of iron floats in water. Please explain this to me.

 

[jtbell]

Compare the density of an iron nail with the average density of the ship. (Is the inside of the ship, solid iron?)

 

[xts]

Oh, come on!
If you drop an empty can it also floats. The ship is not a piece of iron: it is rather a large volume of air surrounded by just a little bit of iron. If you replace the air with water (which happens if you make a hole in the hull) it floats no longer...