Iron needle is compact and its density is 7.6 g/cm3 Thus, as the density of iron needle is more than 1 g/cm3 therefore, it sinks in water. However, the iron ship is constructed in such a way that it is mostly hollow from within, thus, the volume of iron ship becomes very large as compared to its mass and hence its density is less than 1g/cm3 . As the density of iron ship is less than 1g/cm3 , therefore it floats in water.
