Windpilot ... strictly for Cruising
Experience with ultralight displacement boats (ULDBs) of all sizes has taught us that their acceleration and deceleration potential is just too great to entrust to a windvane steering system. ULDBs can plane at up to 25 knots. Every puff translates almost immediately into boatspeed, which makes for a very erratic apparent wind angle. Displacement yachts, in contrast, respond only slowly to changes in windspeed and most are reluctant or unable to plane.
The speed potential of almost all bluewater yachts is directly proportional to waterline length. Monohull ULDBs, on the other hand, have no such restrictions. Bow, underwater profile, keel, displacement and sail area are all designed to promote fast surfing in even moderate wind strengths. Sailing becomes a different game altogether in this territory and windvane steering has no place here!
The ability suddenly to break away and plane leads to rapid changes in speed and, in consequence, equally rapid and pronounced changes in the apparent wind angle. Windvane steering systems steer to the apparent wind angle. A windvane on a ULDB on a windy day might be good for riggers and sailmakers, but not for your nerves or your pocket! The situation is not necessarily any better upwind. The outright speed potential of a UDLB may be lower close hauled, but the sudden jumps in speed remain. Every time a wave or other influence causes the boat to bear away - even just a couple of degrees - the speed increases markedly and the apparent wind moves forward. The poor windvane gear has no way of knowing whether it is steering high and slow or low and fast, as both scenarios yield the same apparent wind angle. Teaching a windvane to distinguish between two different situations that produce the same physical effect is beyond us, so it would appear that for now at least ULDBs must remain out of reach.
An autopilot remains the only sensible choice for other fast planing designs too, at least off the wind. US sailing magazine Cruising World looked at the use of windvane steering systems on BOC yachts in its Issue 9/1999 edition, concluding that "The current boats accelerate and decelerate at such extreme rates that windvane steering appears on few and conservative boats only."