Windvanes 101Crash Course in Selfsteering Systems
Combining Autopilot and Vane Gear
The idea of using a small autopilot connected to the vane gear rather than to the boat's own steering is sometimes brought up. The advantage of this would lie in using the servo power of the vane gear's trim-tab or servo-oar to turn the boat's rudder. By doing that the autopilot would only need a very small motor, which would reduce strain and power consumption. In light air, especially downwind, when the air vane of the vane gear had trouble producing a true and adequate signal the compass of the autopilot would be a better sensor.
During the years we have been involved in several experiments of this kind, especially in connection with solving the self-steering problem on light-weight, planing racing boats in singlehanded transoceanic racing. The objective then is to allow the boat to plane under the spinnaker downwind when the air vane does not have enough apparent wind to function properly. Due to weight and charging restrictions on boats of this type a large autopilot cannot be used. Hence the efforts to combine the vane gear and a small autopilot.
The results of these experiments have been very positive. However, in our opinion the average cruising boat is better off separating the two systems. The vane gear will steer perfectly well any time there is a decent breeze. The autopilot will be used mostly for powering and in very light air when nothing much is asked of it. With this use it is always capable of steering through the boat's own steering, even if it is small and power efficient.
If there are conditions when a combination hook-up of autopilot and windvane make a better solution we certainly recommend it. In our opinion steering by hand should be more or less limited to docking the boat and sailing in and out of harbor.
USING A WINDVANE AND AUTOPILOT AT THE SAME TIME
Some competitors advocate using an electric autopilot and their windvane at the same time in heavy weather, claiming it would provide increased steering stability. This, to us, is nothing more than a tacit admission that their airvane cannot handle the task of steering in heavy weather. A servopendulum system develops more steering power the harder the wind is blowing and the faster the boat is moving. A small auxiliary rudder trying to steer a course according to the source of apparent wind can be overpowered, and attempting to lend assistance by using an electric autopilot that tries to steer a compass course can have the two systems trying to steer different courses as the wind varies. This can lead to strain on both steering systems and possiby even a severe accident at worst - it just does not make sense.