Whether it’s a compass course, an angle to the wind or to a waypoint on the GPS, an electric autopilot is an obedient crew member who always tries to respect the instructions given, the ones you transmitted via the control panel. Connected to sensors (compass, GPS, wind instrument), it processes the information and transmits an order in real time to the ram, connected to the steering quadrant. An obedient crewman, if you understand him and know how to talk to him…
Thanks in particular to research in offshore racing, autopilots have made enormous progress in recent years. But to fully benefit from them while cruising, you still need to know how they work, how to access the different modes and set the right parameters… and not forgetting to trim your sails properly either!
In addition to GPS mode, all the autopilots on the market offer a compass mode or a wind mode which is generally split into apparent or true wind mode (see article on true wind in this blog). Which one should you choose depending on your point of sail?
Here are a few guidelines before pressing the “on” button
Which mode for which point of sail?
Close-hauled, the best results are usually obtained using the apparent wind mode.
On a close reach, and as long as you’re sailing with flat sails (main and genoa), the compass mode works quite well, provided you have set the parameters correctly (see below).
With the wind on the beam and in downwind conditions, especially if there’s a big sea, the true wind setting is the most effective. The boat can subject to strong accelerations and the apparent wind variations are significant. If you keep it set on apparent wind mode, the pilot tends to overemphasize the movements. In particular, remember that when the boat accelerates on a wave, the apparent wind increases, its angle becomes closer (it’ll bear away): the pilot then has a tendency to steer the boat down below what is necessary to maintain a straight wake. So, opt for “true wind”!
Tacking and gybing mode
A change of tack is normally triggered by simultaneously pressing two buttons on the autopilot control head. The tacking angle is generally 100° by default, but this can be set. On a catamaran and especially in light airs, it’s in our interest to increase this value to help the boat pick up again on the new tack.
Which parameters to set?
Rudder gain: This is the basic setting. It refers to the response level of the ram.
Above a certain value, the gyro takes precedence over the compass. The pilot then gives priority to countering the yaw movements instantly recorded by the accelerometer (gyro). As a result, the course-keeping is better.
Counter helm: After you’ve moved the helm over one way, you naturally bring it back beyond the midships position to control the boat’s inertia. When the autopilot reproduces this movement, it’s called the counter-helm. Its setting depends directly on the sea state and the gain level. The more of a cross-sea you have, the more you should increase the gain, but you mustn’t forget to increase the counter-helm setting as well.
For the most perfectionist, you can also intervene (depending on your autopilot model) on the helm coefficient (not to be confused with the gain) and wind smoothing. Access to all these parameters can be more or less user-friendly. The best thing is to make a note of configurations that work depending on the conditions and sail combinations.
And don’t ask an autopilot to hold a course that a helmsman couldn’t! To achieve a straight wake – the obvious sign of a well-tuned autopilot – you must first stabilize the boat as much as possible.
Pictures credit: Nicolas Claris / JMF/LAPROD