Auto Helm auto pilot zigzag

[JWJBigfish]

I have a 26' Glacier Bay with auto pilot. The problem I have only occurs when I am on a northerly course. Generally when I go offshore my heading is a southerly track. It tracks nice and straight as long as I'm headed in a southerly direction. On return, on a northerly course it zig zags all the way back. Any ideas?

[Gil Morgan]

I presume that you have an Auto Helm autopilot that is now the equivalent of the Raymarine ST5000. Are the prevailing seas following when you are heading North??

[JWJBigfish]

Gil, Yes it is an ST5000 and usually the seas are following me in. Does a following sea affect the auto pilot that much?

[Gil Morgan]

Following seas are always tougher to handle even when steering manually, and with a Cat hull, probably tougher than a mono hull.

I did have a Cetrek autopilot that I replaced almost a year ago with a Simrad AP11. The Cetrek is similar to your ST5000 and at trolling speeds with following seas, you could look back at the wake and see a beautiful zig-zag pattern. You could also hear the helm pump working like hell to keep the boat straight. I would not trust the Cetrek in anything but trolling speeds with following seas. I had a couple of unexpected hard-overs that are not fun.

My Simrad has not really been tested, but it seems to do a better job, at least at trolling speeds.

[yachtjim]

Have you screwed with the Gain or Sea State settings? Most autopilots are tunable. If the gain is too low the will make a big zig zag pattern and the boat will not stay on course that well. If it is too high the boat will make quick zig zags that that oscillate back and forth uncomfortable. You need to find a nice place in the middle. I have ne experience with cats, but following seas are definitaly tougher to tame with an autopilot on monohulls.


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[Gil Morgan]

I agree with you on the gain-setting scenario, but you have to be careful with the older autopilots. The higher gain settings will be better at the low speed, following seas conditions and improve the zig-zag problem. However, those settings could be killer if you inadvertently leave the high gain settings in place and go into a high speed mode. That is when you may start throwing people out of the boat.

I don't know about the newer ST5000's but the Simrad AP11 has a dual mode: high-speed lower gain and low-speed higher gain. You can set the transition speed switch from Low to High into the AP11 and it uses the SOG NMEA input to make the change. You can also manually switch modes by pressing a button.

[bej]

I have the autohelm installed on my 22' Glacier Bay. I think the problem is the following sea as described. I work a lot harder when manually steering going with the seas than heading into them. The autopilot is no different. I don't mind the zig zag when trolling as it might help lure presentation. I also don't trust it on the way in (going north or even west) but this is the hull impact not really the autopilot. My bet is that you could put a really high dollar autopilot on and get no better results...

Lefty