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Canting keel

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A canting keel is a form of sailing ballast, suspended from a rigid canting strut beneath the boat, which can be swung to windward of a boat under sail, in order to counteract the heeling force of the sail. The canting keel must be able to pivot to either port or starboard, depending on the current tack.

Purpose and history

The traditional keel serves two functions: lateral resistance, and keeping the boat upright by counteracting the heeling force of the wind. The traditional fin keel, pointing straight down from the boat, provides no righting moment when the boat is level. The heeling force of the wind on the sails is therefore not counteracted until the boat has heeled over by a certain amount, moving the fixed keel to windward of the centerline. The purpose of the canting keel is to allow the boat to develop righting moment when level, by swinging the keel to windward independent of the boat's angle of heel.

With the canting keel handling the ballast functions, lateral resistance and steering can be managed separately with a foil (or pair of foils fore and aft). This allows for much quicker maneuverability than traditional keelboats, with about half the weight usually required for ballast.

A version of the technology was invented and patented by CBTF Technology in the 1990s, and saw its first use in major competition in September 2004, when five boats using the canting keel in the Maxi Yacht Rolex Cup placed ahead of the previously unbeaten world champion Alfa Romeo.

A variation of the canting keel is the 3d keel invented by François Lucas in 1998, which allows movement in three directions (side to side, forward and aft, and rotation).

Current use

Originally used in large maxi yachts such as the maxZ86, canting keels are now beginning to appear in smaller boats such as the Open 60, and the VO70 ocean racing classes, and the even smaller Schock 40 and Mini 650. The Schock 40 owned by Tom Schock famously lost its keel and capsized, illustrating the fundamental problem with complicated keel design: without a keel, most boats cannot float upright.

The VO70 (Volvo Open 70) class boats in the 2006 around-the-world Volvo Ocean Race are perhaps the most well known boats to use canting keels for ballast. While previous years' boats showed a few percent improvement in speed each race (the race is held every four years) the VO70 class are showing a 30% improvement in speed. The 6.5 ton ballast bulb, hanging over 16 feet (5 meters) below the water and capable of canting up to 40 degrees, produces a tremendous amount of righting moment (over 130,000 ft·lbf, or 176,000 N·m with the hull level), allowing the boat to reach speeds of over 40 knots. However, the technology is far from perfect. At least three of the seven boats in competition have had problems with the keels, particularly in the area of sealing the opening through which the keel passes. Unlike a centerboard or daggerboard trunk, the opening for a canting keel must allow significant lateral motion, which requires sliding seals. The boat movistar had problems 200 miles off Cape Horn, when it sprung a significant leak as the sliding plates that cover the keel opening fell off in the middle of the night.

During the night on 20 May 2006, on Leg 7 of the Volvo Ocean Race, movistar's aft keel pivot broke loose and began flooding the boat. The decision was made to abandon ship, and the crew transferred to ABN AMRO TWO, which had lost crewmember Hans Horrevoets two nights earlier. movistar continued to broadcast its position for several days, but an aerial search failed to find the vessel.

References

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