What exactly is a ship?

A ship is a large watercraft that travels the world's oceans and other sufficiently deep waterways, carrying goods or passengers, or in support of specialized missions, such as defense, research, and fishing.

Why are ships painted red below the waterline?

The main reason behind the use of the copper sheet was to stop marine organisms, particularly worms, from making their way to the wooden hull. ... Copper oxide has a reddish tinge, thus giving the paint it's much famous red colour. That is why ships are painted red below the hull.