The Trimaran reference article from the English Wikipedia on 24-Apr-2004
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Trimaran

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A trimaran is a multihull boat consisting of a main hull and two smaller outrigger hulls (amas), attached to the main hull with lateral struts (akas).

The first trimarans were built by indiginous Polynesians almost 4,000 years ago, and much of the current terminology is inherited from them.

Multihull sailboats (catamarans and trimarans) gained favor during the 1960s and 1970s. Modern recreational trimarans are rooted in the same homebuilt tradition as other multihulls, though there are a number of production models now on the market, such as the folding, trailerable designs of Ian Farrier.

Trimarans have a number of advantages over comparable monohulls (conventional, single-hulled sailboats). Given two boats of the same length, the trimaran has a shallower draft, a wider beam, less hull area, and is able to fly more sail area. In addition, because of the wide beam, trimarans do not need the weighted keel required in monohulls. As a result, the trimaran offers much better straight-line performance than a monohull, is able to sail in shallower water, and maintains its stability in stronger winds. However, its wider beam makes it a little more cumbersome to maneuver, so tacking and jibing can be trickier.