Hasler pioneered Sevo Pendulum self steering
systems. His design worked identically to all the newer S/P systems like Aires, Monitor
, WindPilot, etc except they had a vertical wind
sensing vane to control the servo rudder/heading. Later designs went to the horizontal pivoting wind
sensing vane because it was more sensitive, accurate and more powerful at putting input into the servo rudder
especially in lighter air. A horizontal pivoting wind vane
should actually steer a boat and maintain a course relative to wind better than a vertical hinged wind vane
vanes are somewhat limited to the steering
input they can make by the size of their steering
rudder and the force needed to be applied to turn it. WPP and others have used an auxiliary Servo Pendulum to turn the vanes steering rudder. From my experience it has worked very well. The vane will steer the boat if it has any way on in conjunction with a larger wind sensing blade. My boat is 35'/13,000# but the vane originally steered a 44'/30,000# boat all over the Caribbean
and up to SF. The PO said the vane had no problem steering his much larger boat. FWIW, my boat has a terrible weather helm
that is really really fierce as boat nears hull speed
only uses wind force on the wind sensing vane to turn their rudder. Seems like it would have problems in light and heavy air situations but owners say it works just fine. Believe they have a 'gear change' function to handle different wind conditions. Any how, a larger boat will need a larger auxiliary rudder to steer it. Believe the Self Steering
Manufacturers make different sized systems for different sized boats. Variations in helm
force required can be handled by using the boats rudder as a trim tab thereby reducing the force needed to be generated by the vanes auxiliary rudder. Have seen boats larger than 50' that have performed well with wind driven self steering.
Pendulum Servo systems input force to the boats rudder increases with boat speed. At hull speed
, a P/S self steerer will put more force into the steering than you can probably generate. Otherwise, the faster you go, the better they work, except DDW.
DDW issue is common to all wind driven self steering systems. If the boat's speed exceeds the relative wind such as in surfing conditions on a ultra light, the wind vane sees little to no wind or even reverse relative wind and goes clueless on how to steer the boat. Have only had the problem once with our old Westsail under spinnaker
. Yep, those downwind flyer W32s can exceed relative wind in the right conditions. Took the spinnaker
down, winged out the jib
, cut the boat's average speed from 7+ knots to slightly less than 7 knots and the vane worked just fine. Boats with less directional stability and higher acceleration potential may not behave as well.