An autopilot will be a welcome crew member on any boat In most conditions an autopilot will steer more precisely than the best helmsman, never ask for food, drink or time off to go to the head and won't complain even in a cold, driving rain. The helmsman, relieved of the task of constantly correcting rudder position to remain on heading can devote full time to doing what he can do best, observing the total scene and managing the boat.

There are three main types of powered autopilots. Tiller pilots that couple directly to the tiller on a sailboat. Wheel pilots, which work by mechanically turning the vessel's steering wheel or by applying pressure to hydraulic steering systems and pilots using electro-hydraulic or electric motor drives that apply force directly to the rudder quadrant or rudder post. With the exception of pilots on very large yachts, all of these autopilots steer by reference to a magnetic heading sensor. Some can also accept bearing to waypoint information from Loran C or GPS. Some sailboat autopilots can steer with reference to a relative wind sensor.

The most common autopilot magnetic heading sensor is a flux gate, a type of electronic compass. It may be built into the pilot, located in the system control box or a separate module intended for remote mounting. Regardless of where the sensor is located it must be protected from local magnetic fields such as those emanating from wires carrying DC current. Pilots using built-in flux gates may be have to be quite close to the loud speakers for the boat's entertainment system or the speaker in the VHF radio. Loudspeakers contain strong permanent magnets and are common sources of strong magnetic interference. Microphones and cellphones may also contain permanent magnets and can interfere with the heading sensor. If you install an autopilot and find that it steers the boat in small circles it may be because it has fallen in love with the starboard hi-fi speaker. Magnetically shielded marine grade loud speakers should be used if the speaker and the autopilot's sensor must be less than about three feet apart. Remote mounted flux gates are best installed near the center of the boat, at the place of least vessel motion in a seaway. Check the area to be sure there are no magnetic materials stored nearby and that crew or visitors don't decide to put their portable radio or a pile of canned food next to the flux gate.

The flux gate systems in many autopilots include an automatic means for correcting for deviation, the errors created by local magnetic effects. The precise procedure will vary but generally involves nothing more complicated than making a 540° or 720° circle in smooth water. Precise compensation for deviation may not be an issue where the vessel's main steering compass is used as the heading reference.

Sailboat systems offer steer to wind options, using information from an apparent wind direction sensor to maintain the desired relative wind angle. Many autopilots provide a pre programmed 100 degree course change mode for tacking a sailboat.

The power consumption of small boat autopilots is usually quite modest. Tillerpilots on small sailboats can be powered for many hours from a modest size deep cycle battery. The power required to steer even a fairly large boat, 40-50 feet in length, usually averages less than 60 watts, 5 amperes on a 12 volt system.

One of the distinguishing points in autopilot design is the use of a rudder position sensor. A human helmsman makes constant use of his knowledge of the position of the vessel's rudder while holding a heading. Many autopilots are equipped with a rudder position sensor, connected directly to the boat's rudder post. The autopilot is programmed to use this information to ensure that the rudder is deflected only as far as necessary to make a timely correction from an off heading condition. Use of rudder position information greatly improves overall autopilot performance, especially in a seaway. Autopilots that function without knowledge of rudder position will generally steer less efficiently and with less precision than those supplied with rudder position feedback. Some autopilots compensate for lack of a rudder heading sensor by using internal logic to simulate for the heading sensor information, however performance is usually inferior to the real thing.

Although autopilot performance is generally superior to the human helmsman there are some sea conditions where the autopilot is best turned off and steering done the old way, by hand. Following seas can rapidly slew the stern of the boat, often at a rate beyond the steering correction ability of the autopilot. A competent human helmsman has the advantage of being able to sense acceleration, the beginning of boat movement that precedes a readily measured change in heading. Experienced helmsmen will constantly and usually unconsciously correct for the impending heading change. The boat maintains a more constant heading and is less likely to roll excessively. Some autopilots may be equipped an additional sensor, a heading gyro, that can sense the acceleration force that is about to cause a change in heading. With this information, the autopilot, like the expert helmsman, can make small, rapid and effective rudder position corrections.

Many autopilots "learn" the behavior of the boat during a period of time after being set on a particular course. They use adaptive logic, noting amount of rudder offset needed to hold a particular heading. The learning process takes some minutes, therefore it is best to allow the unit to operate for a while before trying to make sea state or other adjustments.

Owner installation of an autopilot need not be difficult and provides the advantage that the boat owner will learn how to make the adjustments required to match the system to the boat. Installation of autopilots that connect directly to the boat's existing hydraulic steering system may benefit from professional help with the plumbing and initial set up of the hydraulic portion of the system. A mistake or a poor installation could deprive the boat of all steering command. Installation of autopilots that are interfaced with other on board equipment may require the assistance of an electronics technician to ensure that all systems are "talking" the same electronic language.

If at any time a steering system problem arises on an autopilot equipped boat immediately turn the pilot off and try hand steering. If the problem persists, open the circuit breaker that serves the autopilot or remove the fuse. On occasion, a defect in an autopilot that is supposedly off but actually partially operating can disable a boat's steering system.