Autopilot and self-steering

An autopilot has a heading/motion sensor, control head, course computer, rudder-angle sensor where required and a drive that moves the rudder. A below-decks linear drive is an electric or hydraulic ram connected to a dedicated tiller arm. A rotary drive turns steering chain or gears. A cockpit wheel pilot drives the wheel and is generally a lighter-duty solution. The computer must be matched to drive current and the drive must be sized for the boat's loaded displacement, steering type and rudder load—not length alone.

Windvane self-steering uses apparent wind and boat motion rather than electricity. A servo-pendulum vane pulls the main tiller/wheel; an auxiliary-rudder system such as Hydrovane steers with its own rudder and can provide emergency steering. These are alternatives or redundancy, not components of the electronic pilot.

Two people cannot hand-steer continuously for weeks. The pilot is operationally critical and often one of the largest passage electrical loads. Undersized drives overheat or break in quartering seas; weak mounting structures fail even when electronics work. A balanced sail plan dramatically reduces load. Redundancy may be a spare drive, repair parts, independent windvane or a practiced method of sheet-to-tiller steering.

First balance sails and remove steering friction. Service connectors, calibration, rudder reference and manufacturer-approved drive wear items. A faulty control head does not require a new ram; a worn ram does not always require replacing a compatible computer. Carry the components most likely and feasible to change—drive belt/motor/brushes or a complete spare ram where practical.

Upgrade when the drive is undersized, mounted to weak structure, unsupported by its computer, or demonstrably unable to steer the loaded boat. An independent windvane adds resilience and reduces power use but requires stern geometry, installation, learning and sail balance. It is not automatically justified on every two-handed boat with a robust spare-drive strategy.

• Covered by a standard survey — powers on, engages, turns the helm, basic sea-trial course holding, visible drive/mount/wiring and obvious leaks/noise. Many surveys test only in calm water.
• Not covered — loaded-displacement sizing calculation, sustained rough-water current/temperature, internal drive wear, network diagnostics and structural engineering of hidden mounts. An electronics/steering specialist review ($500–$1,500) is worth doing before purchase when the pilot is a major advertised asset, old/obsolete, noisy, leaking, or the drive type/model is unknown.

• The broker or owner — “Send the model and serial for computer, sensor, control head, rudder sensor and drive—not just the brand.” “Send purchase/service invoices and a photo of the drive-to-tiller-arm mounting.” “Has it ever disengaged, overheated, blown fuses or failed in following seas?” “What is the measured current draw in calm and rough conditions?”
• The surveyor — “Identify every component and drive rating; inspect structure, pins, stops and tiller arm; test compass agreement and rudder feedback; and run course changes under power and sail. State what remains untested rather than calling power-on a pass.”

Find the actual drive. Look for oil, rust, loose pins, elongated holes, flexing plywood and a hose/wire that can snag. Engage the pilot at the dock only when safe and listen through full travel. At sea, command 20–30-degree turns on both tacks and watch whether the mount flexes or clutch slips. Compare pilot heading with a separate compass. Record current draw and feel the drive after sustained work. For a windvane, check bearing play, bracket cracks, spare vanes and whether the auxiliary rudder can be shipped safely from the boat.