A catamaran (From Tamil 'kattumaram') is a type of multihulled boat or ship consisting of two hulls, or vakas, joined by some structure, the most basic being a frame, formed of akas. Catamarans can be sail- or engine-powered. The catamaran was first discovered being used by the paravas, a fishing community in the southern coast of Tamil Nadu, India. Catamarans were used by the ancient Tamil Chola dynasty as early as the 5th century AD for moving their fleets to invade such Southeast Asian regions as Burma, Indonesia and Malaysia.

Catamarans are a relatively recent introduction to the design of boats for both leisure and sport sailing, although they have been used for millennia in Oceania, where Polynesian catamarans and outrigger canoes allowed seafaring Polynesians to settle the world's most far-flung islands.

In recreational sailing, catamarans, and multihulls in general, have been met by a degree of skepticism from Western sailors accustomed to more "traditional" monohull designs , mainly because multihulls were based on, to them, completely alien and strange concepts, with balance based on geometry rather than weight distribution. However, the catamaran has arguably become the best hullform for fast ferries, because their powering characteristics and spacious arrangements are valuable.

Multihull component terms

There are three terms that describe the components of modern multihulls. The term vaka, like the related terms aka and ama, come from the Malay and Micronesian language group terms for parts of the outrigger canoe, and vaka can be roughly translated as canoe or main hull.

• Aka - The aka of a multihull sailboat is a member of the framework that connects the hull to the ama(s) (outrigger). The term aka originated with the proa, but is also applied to modern trimarans.
• Ama - The term ama comes from the proa. The vaka is the main hull, the ama is the outrigger, and the aka or iako (Hawaiian) is the support connecting the two (not three) hulls. The term ama and aka have been widely applied to modern trimarans.
• Vaka - A proa consists of a vaka, the main canoe-like hull; an ama, the outrigger; and akas, the poles connecting the ama to the vaka.

Catamarans and trimarans share the same terminology, with a vaka, ama, and aka.

Semantically, the catamaran is a pair of Vaka held together by Aka, whereas the trimaran is a central Vaka, with Ama on each side, attached by Aka.