what is a three hulled boat called

A three-hulled boat is called a trimaran. A trimaran is a multihull boat that consists of a main hull and two smaller outrigger hulls, which are attached to the main hull with lateral beams. Trimarans are often used for both passenger ferries and warships, and they have been found to have an optimum location for the outer hulls in terms of minimizing wave generation and consequent power requirements for operating at high speeds with a payload of 1,000 tonnes. Tri-hulls, also called cathedral hulls, are another type of boat with three hulls, but they have a combination M-shaped bottom and are popular with fishermen and sport boat enthusiasts.