Multihull boats are vessels intended for navigating waters that feature more than one hull, or watertight body. Catamarans are perhaps the most recognizable multihull boats, though other styles do exist for specific purposes. A boater may choose such a design to improve stability, especially in rough waters and at high speeds, and to maximize effective deck space. Ferries are commonly designed with more than one hull to improve speed and stability, and to allow for more passenger transport space on deck; many ferries also transport cars, so the extra deck space is especially important.
Catamarans are multihull boats that feature two distinct hulls oriented in a parallel fashion. A deck or frame runs between the two hulls, and this is where passengers and cargo will be placed while the vessel is in motion. This design is stable and fast; the amount of drag through the water is reduced because the hulls do not sink as far into the water as a larger single hull boat is prone to do. These multihull boats may be motorized, or they may be sail-powered; smaller multihull boats are more likely to be sail-powered, though not exclusively so.
A trimaran is similar in design to a catamaran, but instead of featuring two hulls, the trimaran has three. The function of these multihull boats is somewhat different than that of a catamaran; the trimaran features a main hull in the center of the vessel and two smaller outrigger hulls extending from either side of the main hull. The outriggers are connected to the main hull with long struts. A trimaran is much faster and more stable than a single hull boat, though it is somewhat more difficult to maneuver this boat because of its exceptional width. While the trimaran is able to navigate shallower waterways than a single hull boat, it will be unable to navigate narrow waterways where a single hull design might work just fine.
Smaller vessels such as canoes can also feature a multihull design. Some canoes designed for sailing will feature one or more small outriggers extending from the main hull of the boat. This is done to aid in stability on rough waters or high winds. Kayaks may also feature small outriggers designed for the same purposes. These outriggers are usually removable so the boater can paddle freely when the extra stability is not needed. These accessories are therefore usually lightweight and compact.