Ship In A Storm

Special-purpose vessels are not used for transport but for other tasks. Examples include tugboats, pilot boats, rescue boats, cable ships, research vessels, survey vessels, and icebreakers.
Most commercial vessels have full hull-forms to maximize cargo capacity. Hulls are usually made of steel, although aluminum can be used on faster craft, and fiberglass on the smallest service vessels. Commercial vessels generally have a crew headed by a captain, with deck officers and marine engineers on larger vessels. Special-purpose vessels often have specialized crew if necessary, for example scientists aboard research vessels.
Commercial vessels are typically powered by a single propeller driven by a diesel or, less usually, gas turbine engine. The fastest vessels may use pump-jet engines.