Question

A nail sinks in waterwhereas a ship does not. Why?

Answer 1

hloo dear...!!

It is defined by the weight of displaced water. If a nail is dipped, the volume of water it displaces weighs less than that of steel due to lower density thus the nail sinks.However ship works differently. ... So the amount of water it displaces, weighs more than that of hull, which makes it float.

Answer 2

Nail displaces very little quantity of water and by Archimedes' principle when the weight of the object is more than the water or any other fluid it displaces,it sinks while when the weight of object is less than the water it displaces then it floats as in the case of ship as ship displaces a very large quantity of water so as to move even more than its weight. That's the reason behind it. 
Hope it helps.......