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Solved problems · Autopilot · Crew answer

Why does my autopilot wander off course?

An autopilot that weaves or drifts usually has a compass that needs calibrating or moving, slop in the steering, or a boat that is overpowered. Fix the basics before changing pilot settings.

Symptom

On autopilot the boat weaves either side of the course, slowly drifts off heading, or rounds up in gusts, yet it steers fine by hand.

Likely cause

Common causes are a heading sensor mounted near steel, speakers or high-current wiring, or one that was never calibrated; play in the steering cables, quadrant or drive mounting; a misaligned rudder reference; or too much sail, so weather helm overpowers the drive.

Stop now if

The drive or steering grinds, the drive mount moves, or the boat heads toward danger. Know how to disengage the pilot instantly and steer by hand, and keep a proper lookout; an autopilot doesn't watch for traffic or hazards.

The fix, in short

  1. Check the heading sensor location. Make sure the compass or heading sensor is mounted per the manual, aligned fore and aft, and well away from ferrous metal, motors, speakers and high-current cables.

  2. Run the compass calibration again. Repeat the maker's dockside setup and the compass calibration or linearization in calm water, turning slowly as instructed. Check the result against a known heading.

  3. Remove slop from the steering and drive. Look for play at the drive arm, tiller pin, quadrant and steering cables. The drive mount must not flex under load; fix any movement before touching settings.

  4. Check the rudder reference. If one is fitted, confirm it reads center with the rudder centered and moves the right way, and realign it if not.

  5. Balance the boat. Reef or ease the mainsail to cut weather helm. A pilot that holds course in moderate conditions but fails when overpowered needs a balanced boat, not more gain.

Written by Sailor Cruiser crew. General guidance, not an inspection of your boat.

Equipment involved

  • Autopilot: Below-deck, wheel or tiller pilot with heading sensor and optional rudder reference
  • Steering: Cable, chain or hydraulic steering

Related guides

Sources

Background reading we checked while writing this answer. The wording above is our own.

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