Multihull

A multihull is a ship, vessel, craft or boat with more than one hull. Multihull ships (vessels, craft, boats) include multiple types, sizes and applications. Hulls range from two to five, of uniform or diverse types and arrangements

Catamarans are the most common type, with two symmetric hulls. They are used as racing, sailing, tourist and fishing boats. About 70% of fast passenger and car-passenger ferries are catamarans. About 300 semi-submersible drilling and auxiliary platforms operate at sea.

Some ships with outriggers are built, including the experimental ship Tritone (UK) and the first and second sister-ships of the series of Littoral Combat Ships (US). About 70 small waterplan area ships whose hulls have a smaller cross section at the waterplane than below the surface exist.

Multihull ships can be classified by the number of hulls, by their arrangement and by their shapes and sizes.

The first multihull vessels were Austronesian canoes. They hollowed out logs to make canoes and stabilized them by attaching outriggers to prevent them from capsizing. This led to the proa, catamaran, and trimaran plus various outriggers throughout the Pacific.

Individual hulls are connected by an above-water structure called the platform or above-water bridge. The structure can be watertight partially or fully, or can consist of separate connections.

The distance between hulls is called the transverse clearance and can be measured between center planes or between the inner boards.

The distance between the design waterplane and the bottom of the above-water platform (wet deck) is called the vertical clearance.

The longitudinal distance between a triple-hull ship is called the longitudinal clearance and can be measured between the middle of the hulls or between their fore perpendiculars.

An outrigger is a small side hull attached to the main load-carrying hull by two or more struts.

Proas have one hull and one outrigger. Engines are commonly placed on the main hull.

A ship with one hull of conventional shape and two small side hulls (outriggers) is called an outrigger ship. This type is identified as trimaran in English language publications.

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