Question

Why does a needle sink but a ship floats?

Answer 1

An iron ship (or any metal ship as is the modern standard) floatsbecause it is shaped such that it will contain air within its hull and therefore the average density of the ship as a whole including cavities and all the air space is less than the water and therefore it floats.

Answer 2

there are two reasons for why does a needle sink but a ship floats:
1) the ship has a streamlined shape whereas a needle has a pointed shape.
2) this is so because of the buoyant force acting on the ship is more than on the nail. the density is less for the ship