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Self-steering gear

Self-steering gear is equipment used on ships and boats to maintain a chosen course without constant human action. It is also known by several other terms, such as autopilot (borrowed from aircraft and considered incorrect by some) and autohelm (technically a Raymarine trademark, but often used generically). Several forms of self-steering gear exist, divided into two categories: electronic and mechanical.
Electronic self-steering is controlled by electronics operating according to one or more input sensors, invariably at least a magnetic compass and sometimes wind direction or GPS position versus a chosen waypoint. The electronics module calculates the required steering movement and a drive mechanism (usually electrical, though possibly hydraulic in larger systems) causes the rudder to move accordingly.
Depending on the sophistication of the control unit (e.g. tiller pilot, steering wheel attached Chartplotter, ...), electronic self-steering gear can be programmed to hold a certain compass course, to maintain a certain angle to the wind (so that sailing boats need not change their sail trim), to steer towards a certain position, or any other function which can reasonably be defined. However, the amount of power required by electrical actuators, especially if constantly in action because of sea and weather conditions, is a serious consideration. Long-distance cruisers, which have no external source of electricity and often do not run their engines for propulsion, typically have relatively strict power budgets and do not use electrical steering for any length of time. As the electronic autopilot systems require electricity to operate, many vessels also make use of PV solar panels or small wind turbines on the boat. This eliminates extra pollution and cuts costs.
The main goal of a mechanical self-steering gear is to keep a sailboat on a given course towards the apparent wind and to free the helmsman from the steering job. An advantageous side effect is that the sails are kept in optimal angle towards the apparent wind and deliver optimal propulsion force by that. Even in sailboats running under engine, the self steering gear can be used to keep the boat heading into the wind to easily set or change sails (exception: sheet-to-tiller principle).
On the small motor pinnace Arielle, a 13-metre boat propelled by a 65HP French made Baudouin diesel engine which sailed from New York to Le Havre in 1936, the task of steering a motor boat in the Atlantic swells was more daunting. Arielle had two rudders; the main one under the hull, in the propeller race, was for manual steering and the smaller auxiliary rudder was transom mounted. This auxiliary rudder could be mechanically driven by a special wind vane mounted atop of the coachroof consisting of two rectangular airfoils set at an angle on a vertical axle and balanced by a counterweight. It was simple and worked quite well, but could not steer the boat in very light breezes or flat calm.
Modern servo pendulum self-steering devices with optimized transmission and low friction mechanics are more and more used for day sailing and cruising; formerly being used mainly for long distance ocean passages. The increased low wind capabilities of optimized, modern devices enable downwind steering down to 1.3 m/s apparent wind and 1.5 kn of boat speed properties that make an electronic steering device nearly redundant and enable crossing the doldrums under wind vane self-steering. An increasing number of long distance regatta sailors are using wind vane self-steering because of the fact, that the sails are always kept in optimal angle towards the wind, and hence the speed of the boat is kept at the possible maximum.
For quite a long time there was little development in the self steering systems that were available commercially. Most new developments came in the form of self-build systems. Crucial roles were played by Walt Murray, an American who published his designs on his website. and Dutchman Jan Alkema who developed a new windvane, the so-called Up Side Down windvane (USD for short, commercially available from only two brands) and a new kind of servo pendulum system that could be fitted to boats with a transom hung rudder. For this last invention Jan Alkema was rewarded the John Hogg-Price from the AYRS ( Amateur Yacht Research Society) in 2005. Jan Alkema published a lot of his inventions on Walt Murray's website.

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