A cargo ship or freighter is any sort of ship that carries goods and materials from one port to another. Thousands of cargo carriers ply the world's seas and oceans each year; they handle the bulk of international trade. Cargo ships are usually specially designed for the task, being equipped with cranes and other mechanisms to load and unload, and come in all sizes. Specialized types of cargo vessels include container ships and bulk carriers. ( Tankers and supertankers are also cargo ships, although they are habitually thought of as a separate category. )