I only have experience with my own autopilot, an old(ish) Raymarine
ST4000+ wheel pilot. Different models may work differently, but there also may be some universal similarities. So I'll offer my own experience here.
I have used OpenCPN to run my autopilot in "Track" mode. (I hope to try "Wind" mode next season when my transducer comes in.) As others have said, O
sends various bits of information to the autopilot. It's more than just XTE, though. It's also BTW (bearing to waypoint), DTW (distance to waypoint), and speed (SOW from paddlewheel or SOG from GPS). All these things are used to optimize the AP's response. From what I can tell, BTW is the first thing it uses to set an approximate course, then it monitors change in XTE to tweak the steering over time to compensate for current
and other drift factors. Speed and DTW are used to adjust the gain so that the AP does not over- or under- correct. For example, faster speed causes the AP to make smaller adjustments because the boat will respond more sensitively at higher speed. This is probably similar for other autopilots because it is based on generic PID control theory.
When you arrive at a waypoint (check documentation
for LOTS of info on this), O
sends the next waypoint to the AP. My AP responds to this with a prompt at the control head
which you MUST respond to before it will turn. If you don't respond, the boat will maintain its heading forever. I believe that this is an important safety
feature that is probably similar in other autopilots. Believe me, you really don't want any machine taking over to such an extent that it could steer you onto a different course without permission. For AP manufacturers, that would seem to be inviting lawsuits, which is why I suspect other APs may be the same. (Others can correct me, though, since I'm speculating here.)
Like others here, I can initiate a manual dodge maneuver while the AP is still in pilot, track, or wind mode. Just press +10 or -10, and it turns. Once the dodge is over, I press the opposite button to turn back. It is possible that if you did not do this, the boat would gradually correct back to head
for the original waypoint - I have not tested this, since I consider it more prudent to just "undo" your dodge maneuver.
If you want to control the AP from another part of the boat, try to find a remote control. That's what I bought for my boat, and it is very useful for advancing to the next waypoint or dodging crab pots from the bow. My remote also beeps along with the control head when it's time to go to the next waypoint, so I can respond to it from wherever I am on the boat.
I really think that an automated response to an AIS alarm
is a bad idea. Some things are dangerous enough that an alarm with manual operator override is the only prudent response. So many things could go wrong with an automated steering correction that I doubt any chartplotter
developer would be willing to accept that liability. Technology is a wonderful thing, but every once in awhile you need to look up from the screen
and take control yourself. Even if this were built into O
, my AP would still require manual acknowledgement of any change in BTW.