Merchant ship

They come in a myriad of sizes and shapes, from six-metre (20 ft) inflatable dive boats in Hawaii, to 5,000-passenger casino vessels on the Mississippi River, to tugboats plying New York Harbor, to 300-metre (1,000 ft) oil tankers and container ships at major ports, to passenger-carrying submarines in the Caribbean.

[2] During wars, merchant ships may be used as auxiliaries to the navies of their respective countries, and are called upon to deliver military personnel and materiel.

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, often being equipped with cranes and other mechanisms to load and unload, and come in all sizes.

Bulk carriers can be recognized by large box-like hatches on deck, designed to slide outboard or fold fore-and-aft to enable access for loading or discharging cargo.

The dimensions of bulk carriers are often determined by the ports and sea routes that they need to serve, and by the maximum width of the Panama Canal.

The use of such large ships is in fact very unprofitable, due to the inability to operate them at full cargo capacity; hence, the production of supertankers has currently ceased.

See Braer, Erika, Exxon Valdez, Prestige and Torrey Canyon for examples of tankers that have been involved in oil spills.