We've found that if you tune the AP for, say, motoring in calm conditions at hull speed, she's too insensitive to handle the heading under sail in some chop or waves, esp close hauled.
For a long sail, off the wind, I might bother to retune it, but mostly we use it for setting and dousing sail, long windless days, and for short term departures from the wheel..
After all, as coastal cruisers if we're sailing, we prefer to steer anyhow.
Ditto here. I've had a lot of experience with PID controls in manufacturing processes, and the concepts are exactly identical. The "proportional" part of PID is your gain setting, the "integral" part is referred to as "AutoTrim" by Raymarine, and sums up the cumulative error in your bearing or track, gradually increasing the amount of correction to bring the boat to the setpoint. You can basically tune these parameters for motoring or
for sailing, but not both. And even when tuned for sailing, it may be unreliable unless you're REALLY GOOD at balancing the sails, because conditions can push the boat off its course in ways that your own senses will detect, but the AP will not. (For instance, you will immediately notice a change in heel and subconsciously adjust - but most APs will not detect this at all.)
To summarize, most modern APs have three modes:
- "Standard" bearing mode, where you press a button the AP locks onto the bearing (from its integrated compass) and keeps the boat pointing in the same direction. Actual COG can/will vary as current and/or wind push you in a different direction that you're pointing. This is the most commonly used mode, because it requires no interfacing - though to really use it you need to tune the controller parameters.
- Track mode when interfaced with a chartplotter, where you set a waypoint and activate a course to the waypoint. When you press a "track" button (or similar) to activate, the AP starts out pointing your boat toward the waypoint, but as current or wind push you off course (increasing XTE - cross-track error), the AP will change your bearing to eliminate the XTE and keep you on course. IMO this is best used when motoring - under sail, this could cause you to point higher into the wind than your boat is capable of, or worse, to broach. But apparently many people do use it for long-distance cruising.
- Wind Vane mode when interfaced with an electronic wind sensor. When activated the AP calculates your bearing relative to wind, and keeps you there. Supposed to work like a real wind vane.
How many of you have an actual wind vane? I have a friend who bought one a couple years ago, and has mixed results.