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Old 07-24-2007
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No catamarans that I know of plane.

The general formula of 1.34 x SQRT (LWL) doesn't generally apply to most multihulls, including the "non-performance" cruising multihulls.

Most cruising catamarans have a waterline-to-beam ratio of 6:1 or so. Most trimarans have amas with a hull ratio of around 12:1, and main hulls of around 8:1 or so. While they are technically displacement hulls, the high waterline-to-beam ratio often means that they are not subject to the 1.34 * SQRT (LWL) limit, as keelboats generally are. In many cases, they have a hull speed formula of 2.0 * SQRT (LWL) or higher, depending on their exact hull design.

On my 28' trimaran, I've seen speeds of over 15 knots under sail, and generally we can run down most of the monohull sailboats that sail in the area around us.

Monohull keel boats can often exceed the calculated hull speed due to several reason. First, when they are sailing down the face of a wave, or surfing, they can exceed hull speed. Second, when they are being pushed by a following current, they can exceed hull speed as their Speed Over Ground, but may not be exceeding their calculated hull speed relative to the water. Finally, some of the smaller keelboats can plane...but not too many of the larger keelboats can or will.
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