SVN solovelanet

38 SVN Solovelanet Global The L-shaped, and even more the trapezoidal keel, will be less affected by chopping seas, although their performance will continue to be limited by their lower righting moment and a reduced bowline angle. In terms of overall performance, obviously much will depend on the general design of the boat. The twin keel Boats with a twin keel, such as the increasingly wide- spread RMs, are no longer a strange sight. They are common with some French shipyards and the rea- sons behind them are mostly practical. In areas with a very strong tidal excursion, as is often the case in France, a twin keel allows the boat to maintain a low draft without losing lift, the lateral force that genera - ted by the flow of water on the keel, which counters leeway. Also, in an emergency it can serve as a cradle, allowing the boat to sit on the two appenda- ges at low tide, while remaining perfectly balanced. With strong winds, and particularly when sailing clo- se-hauled, a twin keel with low draft is more effective than a single shallow keel, while its lift remains close to that of a deep fin. With light wind, however, the twin keel is rather penalizing because of its higher volume, which causes significant resistance to water. The canting keel A canting keel is a keel with a mechanism that allows it to be inclined right or left. Nowadays it is quite normal to find canting keels on racing boats, espe- cially oceanic ones. But experiments with movable keels have a long and complex history. A patent for a canting keel of sorts was granted to one Douglas Beardsley as early as 1900. In modern times, a mo - veable keel was used for the first time in a long race in the 1991 Mini Transat, by Michel Desjoyeaux, who won the second stage of the regatta hands down. It was not, however, a canting keel as we intend it today, but a swing keel, i. e. a longitudinally-moving keel that could be pulled up under the hull when sai - ling downwind, reducing drag. The first canting keel to be used in an off-shore race was that adopted by Englishman Pete Goss in the 1996-7 Vendee Globe. The main function of a canting keel is to regulate the righting moment. It is moved windward when sailing either close-hauled or downwind under strong win - ds, helping keep the boat more upright and increa- sing performance. Under light breeze the opposite effect is sought by moving it leeward: the boat is slightly heeled over, reducing the wet surface and therefore the resistance to water. From a structural point of view, designing a boat with a canting keel is no easy task. Keel design Trapezoidal keel This shape, that was widely used in the 80s and part of the 90s, has a large area, but little depth. The weight is heavier at the top, where the area is larger. Its efficiency is not comparable to the other two types, but the strain imposed on the boat is also lighter A boot keel has a much narrower profile than a trapezoidal keel, and most of its weight is concentrated in the boot. It is the most widely used keel for cruise boats, because the boot does not risk to get entan- gled in suspended ropes in harbours, as instead might happen to T-shaped bulbs T keel The T-shaped keel is the preferred shape for regattas. It concentrates its weight at the bottom, and is very efficient in develo- ping a strong straightening torque. The fin is often made of a different mate- rial than that of the bulb, such as steel or carbonOn the other hand, it makes it harder and more un- comfortable to sail under rough sea Boot keel

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