Self-steering gear

Self-steering gear is equipment used on sail boats to maintain a chosen course or point of sail without constant human action.

Mechanical or "wind vane" self-steering started out as a way to keep model sail boats on course. Before the advent of radio control, model yacht racing (started before WW1) was typically contested on long narrow ponds, and the number of stops along the banks was counted as a penalty in the final result. Initially a system of counterweight on the tillers was devised to compensate for the weather helm when the model boat heeled in a gust. These crude systems evolved in a more sophisticated system called Braine Gear after its inventor, George Braine. The Braine steering gear was a fine-tuned system of quadrant on the rudder stock driven by the tension of the mainsail sheet and damped by a rubber band. A more sophisticated system called the vane gear was later devised, it relied on a small vane or airfoil driving the main rudder via an adjustable system of clockwork gears. It was very similar to the later vane driven autopilots seen on transatlantic yachts such as Blondie Hasler's self steering rudder. Some transatlantic singlehanded sailors used a crude form of self steering devices to cross the Atlantic Ocean in the 1920s and 1930s, the most notable being Frenchman Marin Marie (Paul Marin Durand Couppel de Saint Front) who crossed the Atlantic twice in the 1930s, first on a sailing yacht called Winnibelle II and secondly on a motor pinnace called Arielle.

Self steering aboard Winnibelle II on its Atlantic crossing from Douarnenez, France, to New York in 1933 was somewhat similar to a Braine gear, using twin jibs (Trinquettes jumelles) with their sheets connected to the rudder via an array of blocks and lines. The long keeled Winnibelle II was perfectly stable on course on close-hauled or beam reach points of sailing but the self steering twin jib system could take over in the trickier downwind broad reaches and running points of sailing.

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.

While Marin Marie was fitting out Arielle in New York he was approached by a French inventor named Casel who offered to fit an electrical autopilot of his invention, free of charge. The Casel autopilot was using the then revolutionary photoelectric cells and a system of light and reflecting mirrors on the magnetic compass rose. Its principle is somewhat similar to modern day electronic autohelms, excepting the modern flux-gate sensor for autopilots system. The Casel autopilot, which included an array of green, red and white telltale control lights, used an electric motor to act on the main rudder. Though its basic principle was sound and was useful in some sections of the passage, it proved to be somewhat too lightly built for a wet vibrating little boat and was trouble ridden. Marin Marie, though appreciative in some occasions generally loathed the temperamental device, specially when he discovered that Casel had inadvertently hidden his stores of Bordeaux wine in the autopilot compartment, unwillingly condemning him to a teetotal Atlantic crossing of some 20 days.

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.

There are several possibilities for the interface between the drive mechanism and the conventional steering system. On yachts, the three most common systems are:

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 photovoltiac (PV) solar panels or small wind turbines on the boat. This eliminates extra pollution and cuts costs.