Windvanes 101—Crash Course in Selfsteering Systems


In an autopilot a compass sensor governs an electric steering motor connected to the yacht's rudder. The operating characteristics of the pilot can be more or less sophisticated. In a simple, vintage, so-called hunting pilot the motor turns the rudder every time the sensor compass registers a different heading from the preset course.

Today even small and inexpensive autopilots are more sophisticated than this, providing some kind of feedback control, which prevents the pilot from constantly steering the boat back and forth across the course line. A deadband refers to an area around the set course within which deviations are tolerated and do not produce any steering response. Often the deadband can be varied for different conditions. The function of the deadband is to allow the boat to come back to course by itself and so to conserve power and prevent over steering.

The term "gain" refers to the amount and speed of the rudder movements induced by the pilot and can also be adjusted to fit the existing conditions.

Development in autopilots is making them more and more like computers, where the feedback will no longer be static, but will use a memory to register the boat's course performance and continuously adjust deadband and gain for optimum steering.

The ultra-sophisticated autopilot can be interfaced with GPS, sat nav, loran and log to steer between waypoints, readjusting itself according to the input from the other instruments.

Autopilots can be divided into two major categories:

1. Cockpit Mounted Pilots

The small cockpit mounted pilots which are inexpensive and use little electricity but are not intended or recommended to be the sole self-steering aid for the oceangoing cruising boat. On most boats they have real difficulty steering in rough weather. They are ideal for occasional use, preferably in light to moderate conditions and for powering.

2. Under Deck Pilots

The under deck pilots which are much more heavy duty but also require a lot more electricity. Their price is often three to four times that of the smaller cockpit-mounted pilots, and these below deck auto pilots often need professional installation.

Mechanical Windvane Selfsteering