Question

Why ship does not sink in water even it is heavier than water??​

Answer 1

The amount of water it displaces weighs as much as the ship. The weight of the ship pulling down and the upthrust pushing up are equal and opposite forces, so the ship floats.

Answer 2

Although ships are made of materials that are much denser than water, the density of a ship itself is its total weight (including, cargo, bunkers, stores, crew, etc.) divided by the external volume of the hull. This means that the hull must have an external volume that is big enough to give the whole ship a density that is just less than that of the water in which it floats.