Autopilot: S shaped course

[ichorniy]

I have older ST 30 autopilot which I seldom use because if you motor or go downwind autopilot tend to steer S shaped course and swings up to 10 degrees of original course. The only time I can use auto pilot is on beam reach or close-hauled if sails are well balanced but even then I get up to 5 degree variation from original course.

It seems that with no wind or downwind autopilot over corrects from side to side.

Is this normal behavior for autopilot or my unit is old or undersized?

[sailingdog]

Can't really say whether the autopilot is undersized, since you don't say what boat you have...

There may be some adjustment you can make to the autopilot in terms to help compensate for the problem you're having.

However, I'd point out that the newer models will have better electronics and better software than the model you have, and may give significantly better performance.

[ichorniy]

Thanks for reply Sailingdog.

I have Hunter 29.5 and ST30 autopilot which is probably as old as boat: 15 years.

[sailingdog]

It appears that your pilot is not documented at Raymarine's website. I'm guessing it is a model that was discontinued by Autohelm before Raymarine bought them out. However, I'd point out that the calibration and adjustment routines are probably very similar to that of the Autohelm units that were in production when Raymarine bought them, so looking at a manual from one of them may give you some idea of what to do.

[TimJedda22]

I have the ST1000 on my 22ft, you can adjust it to react to 1 deg or 10 deg depending upon what you want - obviously the 10 deg uses less power...it also "memorises" the sea state to stop reacting to minor movements.

[bljones]

do you have a "gain" knob? If so, try to adjust it to even out the course corrections.

[RhythmDoctor]

All controllers need to be tuned to work properly. A poorly tuned controller will not track well, no matter how new it is. And the proper tuning parameters may have changed if you tend to sail in different conditions than a prior owner who tuned the controller to his sailing preferences.

The "S" shape you describe sounds like the controller is overcorrecting, and its gain may actually be too high. So you should experiment by trying lower gain (and also higher, for comparison).

Many controllers are based on the traditional "PID" control logic (proportional, integral, differential), and have three adjustments that correspond to each (though they may adopt different terminology). The gain corresponds with the "P" part. If your controller follows this design, you may also reduce the "S" tendency by increasing the "D" component.

Take this advice with a grain of salt - I have not actually tuned my autopilot yet. It's on the list (because it has some issues under certain sail conditions), but I have other more important things to work on first.

[ichorniy]

Thanks for all replies. I guess i will get manual and will try to tweak it if I can.

[whroeder]

Other possibilities is no signal from rudder position sensor
or wind sensor in wind mode.

[Omatako]

I'd be suprised if a unit that old would have a wind mode but it may. That however is probably not the problem. I agree with other posts - it's probably in the settings of sensitivity and rudder gain both of which are adjustable and will help the AP steer a better course.

Then again, you don't happen to have a big steel buckle on your belt and are walking around the cockpit wondering what's going on with the AP??