The Helmsman's Friend -
A Sailboat Autopilot

A sailboat autopilot is a thirsty beast, drinking your battery juice as if its life depended on it - which of course it does. So is it best to forego one of these and hand steer all day, for mile after mile, hour after hour? I don't think so...

So, providing your boat's batteries can keep up with its electrical appetite, an autopilot deserves a place on any sailboat, large or small.

Whilst larger boats will need a powerful inboard type working directly on the primary steering mechanism, one of the cockpit models will suit the smaller boats.

There are two cockpit versions of autopilots - one for wheel-steered boats and another for tillers.

All types rely on fluxgate compasses keep them on the straight and narrow.

Cockpit Versions of Sailboat Autopilots

For Tiller-Steered Sailboats

Autopilots for tiller steered vessels - or 'tillerpilots' as they are widely known - are the simplest form of sailboat autopilot, in which an electric motor is connected via a transmission mechanism directly to a push rod. The push rod extends or retracts to move the tiller.

Small tiller-pilots, suitable for boats up to around 4,500kg displacement, consist of a single module which includes the compass, the control unit, the motor and push rod.

In larger models, suitable for boats up to around 7,500kg displacement, the control unit and compass are separate modules. All tiller autopilots tend to be a little noisy - rather like the distant yapping of a small dog.

For Wheel-Steered Sailboats

Autopilots for wheel steered vessels are very similar to the tiller version, except that course corrections are applied to the wheel by a belt, rather than a pushrod.

Many offshore sailors choose to equip their sailboats with both windvane self-steering gear and an electronic autopilot - the former to steer the boat when sailing and the latter for use under power, when the electrical supply will be plentiful. 

A Fully Integrated Sailboat Autopilot System

In recent years the trend towards instrument system integration has extended to include those cockpit autopilots that have a separate control/display unit.

A Fully Integrated Sailboat Autopilot SystemA typical, fully integrated system

To get the most out of such units you need to integrate them with a compatible GPS or chartplotter, and a wind instrument either mounted at the masthead or at the stern of the boat. This gives three main operating modes:~

  • Auto - the autopilot is locked onto a heading;

  • Track - the autopilot is locked onto a track between two waypoints;
  • Wind Vane - the autopilot maintains a course relative to the apparent wind. However, in practice if there's much of a swell running, neither a masthead instrument nor a stern-mounted one will give a particularly satisfactory result. The masthead unit will suffer from the motion of the boat, and a stern-mounted unit will be operating in a disturbed airflow. The resulting impulses have to be damped and processed to obtain a useful signal.

All sorts of data display and functionality is now available on the display unit - cross-track error, off-course alarm, waypoint proximity alarm, windshift alarm and so on.

One very useful function is 'Autotack', initiated by some judicious button pressing. Great news for a short-handed crew, who can now deal with the sails while the autopilot is putting the boat about.

Inboard Sailboat Autopilots

This type of autopilot can do all of the clever stuff mentioned above and lots more, being usually fully integrated with the boats navigational system.

They're much more powerful than the cockpit versions, suitable for large sailing boats and power boats, and a deal more expensive as a result.

Instead of connection to a tiller or wheel, they use push rods or hydraulic systems connected to the rudder post (or quadrant) to turn the main rudder directly.

Feeding the Beast

Power consumption of an electronic sailboat autopilot can be significant, the key factors affecting it being:~

  • Sail trim - poorly trimmed sails and excessive weather helm;

  • Sea state - bigger seas and increased yawing require more frequent steering adjustments;
  • Autopilot setting - the more precise the course setting, the greater the work to be done by the autopilot;
  • Boat displacement and waterline length - the more boat there is to move, the greater the greater the work to be done by the autopilot;
  • Underwater shape - notwithstanding the tracking properties of a long-keeler, a keel-mounted rudder will require more force because it's impossible to balance, whereas a fully balanced spade rudder will be lightest on the helm.

It has to be said though, that if your battery charging regime has a weakness, an electronic sailboat autopilot will find it.

Linking a Tiller Pilot and a Vane Gear.

By removing the windvane from a vane-gear and connecting a small tiller autopilot in its place you can now use a vane-gear when under power. The pendulum or trim-tab now works with the autopilot, greatly reducing power consumption.

Some windvane gears, like the Auto-Helm and the Windpilot Pacifics for example, are constructed with this in mind and have the connection fitting built in. Other vane gear manufacturers don't recommend this approach, believing that the turbulence of the prop-wash can damage the pendulum blade bearings.

Next: Comparing a Sailboat Autopilot with Self-Steering Gears...

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