Autopilot woes

[mike]

Our autopilot (ST4000mkII) works fairly well under sail, and while motoring slowly with the rudders down. But motoring at moderate to fast speeds (with rudders up, of course), it's a different story. I'll get myself settled in on the desired course, and engage the AP. After a few moments, the boat might start to drift off course, and the AP begins to apply a little bit of correction. But it gets impatient... when that corrective helm doesn't move the boat back on course, it applies even more, unaware that it is overcorrecting and that it just needs to be a little patient for small helm adjustments to show an effect. More and more steering is applied as the boat then begins to veer back towards the desired course. Because it steered so hard to get back on course, it overshoots and goes off course to the other direction, then tries to get back to the correct course, overshooting again.

This continues indefinitely, veering off course 15-20 port, 15-20 stbd, 15-20 port, etc. (even after giving it plenty of time to "settle in" to the right course).

I've tried changing virtually every setting on the AP (response, rudder gain, autotrim, etc.). Some of these settings help, but none eliminate the problem. If the coast guard or sheriff sees me, I'm likely to get stopped for boating under the influence! And I don't even drink.

Anyway, after reading through the manual, I think I might need a rudder position sensor. It is supposed to help this kind of situation. But I thought I'd ask here first to see how other peoples' autopilots work.

--Mike

[Frank C]

Our autopilot (ST4000mkII) . . . This continues indefinitely, veering off course 15-20 port, 15-20 stbd, 15-20 port, etc. . . . If the coast guard or sheriff sees me, I'm likely to get stopped for boating under the influence! And I don't even drink.

Mike, just tell the Coasties that yer Pilot has been sniffin' gasoline fumes!

[Dimitri-2000X-Tampa]

Mike, before you invest in one of those gadgets, you should go through the electronic compass calibration procedure. In involves taking the boat to a nice calm and fairly open area, punching in a few select codes, then making very slow 360's with the boat until the machine says its better. These electronic compasses get out of whack and then it won't steer worth a damn anymore. Even the one on my watch went out of whack a couple months ago and I had to recalibrate that. Look it up in your manual.

[Eric Lowe]

Have you tried dropping the centerboard just a couple of inches? This may help to keep it tracking straighter. Also, I thought these newer autopilots were supposed to "learn" the steering characteristics of the boat over time depending on the sea state, etc. Have you given it ample time in open water to settle itself down?

One other point, somewhat related to the fluxgate compass calibration: Are you only using the autopilot for a given direction?...say NW for example....perhaps there is more compass deviation on a particular course? Maybe changing the location of the compass would help. I usually mount them way down in the bottom of the hull next to the ice chest compartment (just under the little fiberglass "step" aft of the ice chest) which seems to have worked out quite well....typically away from any large magnetic objects unless you have a fire extinguisher there with iron in the jacket?

Eric Lowe

[mike]

Mike, before you invest in one of those gadgets, you should go through the electronic compass calibration procedure. In involves taking the boat to a nice calm and fairly open area, punching in a few select codes, then making very slow 360's with the boat until the machine says its better.

Yes, I had done that when I originally installed it, and I did it again yesterday... didn't seem to help.

--Mike

[mike]

Have you tried dropping the centerboard just a couple of inches? This may help to keep it tracking straighter. Also, I thought these newer autopilots were supposed to "learn" the steering characteristics of the boat over time depending on the sea state, etc. Have you given it ample time in open water to settle itself down?

That's what I thought too... I let it swerve back and forth for about 15 - 20 minutes, and it never seemed to catch on to the fact that it was repeatedly over-correction.

One other point, somewhat related to the fluxgate compass calibration: Are you only using the autopilot for a given direction?...say NW for example....perhaps there is more compass deviation on a particular course?

Yesterday, I used it going to my destination (SW) and back home (NE)... it could have been my imagination, but it did seem like perhaps it was behaving worse on the NE heading. I'll take it out again soon and check how it performs on various headings.

--Mike

[Rolf]

Mike,
That is incredibly disappointing but timely info. I was about to spring for the st4000, but now not so sure. I motor regularly to Catalina, no ballast, fully loaded, wife and kid, 14-15 knots. Please keep us updated as you continue to experiment with c/b, speeds, etc.

There is no doubt that the 50hp most of us have is probably underpowered for such a large vessel at speed. God knows I've had to wrestle her a bit in moderate seas to keep a straight line. The st4000 is specifically made for small, slower than power sailboats. Perhaps raymarine could answer the "speed" issue?

One more thing-- Do you and others here use the auto to raise sails when soloing? That would be reason enough for me to invest.

Rolf
2002x-Albatross

[Tony D-26X_SusieQ]

I don't have any experience with the ST4000 but I have a sportpilot ap. There is a sensitivity setting when you turn the sportpilot on. Two or three clicks and you are fine more than that and the boat starts the dance. It also goes crazy if you get around someone using radar. That however would be a sometime thing. If it is doing it every time I would check for the sensitivity thing then the fluxgate compas.
Rolff
I use mine a lot when I have to tend the sails. It is worth every penny of the cost there.

[Jack O'Brien]

When my refurbed SportPilot went bad RayMarine upgraded the motor to the "Plus" and recommended the rudder position sensing transducer- which I got. Their Tech guy said the transducer is helpful if one has excessive "slop" in the steering system and the boat "S"s. I have about 1/8 wheel turn of slop in my system mostly due to the rudder/steering bar holes and pins. (Teleflex rack & pinion) Don't know if this is "excessive" or not.

Just installed the transducer before recent 70-mile trip Key West - The Dry Tortugas. Haven't calibrated my compass nor done any comparitive testing. Did notice on trip at one point (motor sailing ?) that the boat was holding GPS course over ground at + or - one degree. The lowest or second lowest level of sensitivity seemed to work best. Haven't tried the SportPilot at speed but know the boat is really squirly at speed.

The autopilot was a Godsend for my single-handed trip. Lets one set sails into the wind, get beer from below, release used beer, etc. I even managed a couple naps under way.