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Experience with ultralight displacement boats (ULDBs) of all sizes has shown that the speed potential of these flyers is just too great to be effectively entrusted to windvane steering. Every change in wind speed aboard such responsive boats produces a change in boatspeed which, in turn, changes the apparent wind angle. The acceleration and deceleration of the boat through puffs and lulls causes the apparent wind angle to move forward or aft. A

windvane gear steering to a particular set wind angle would as a result have to head up or bear away every time the wind speed changed in order to maintain the set angle.

Most monohulls, and virtually all cruising boats, are limited in terms of speed as a function of their length along the waterline and do not accelerate fast enough to provoke significant changes in the apparent wind angle. Monohull ULDBs have no such restrictions on speed. Bow, hull shape, keel, displacement and sail area are all conceived to promote surfing even in fairly moderate winds; the design encourages tremendous acceleration, inevitably accompanied by tremendous fluctuations in the apparent wind angle.

This type of sailing is quite simply beyond the capabilities of any windvane gear. The kind of wild course produced by any system relying purely on the apparent wind angle would bring the rig down sooner or later, for example in a sudden crash gybe. Things do not necessarily look any brighter on upwind courses. Even with the sails close-hauled, the smallest deviation to leeward (in a swell or a yawing movement) causes the boat to accelerate rapidly, in turn pushing the apparent wind forward. A windvane has no way of telling whether the boat is travelling slower on a very high course or faster on a deeper course, because the apparent wind angle is identical in both cases. This really does represent the end of the line for windvane steering, since there is no way of educating a windvane to distinguish between different situations which generate the same physical effects. Autopilots offer the only effective solution here.

Off the wind, and to some extent even upwind, planing yachts are beyond the scope of windvane steering. Cruising World agreed in its 9/95 edition regarding the use of windvane steering systems in the BOC that, "... the current boats accelerate and decelerate at such extreme rates that windvane steering gears appear on few and conservative boats only."

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