Wandering autopilot

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   Our AP has not been holding course lately. It seemed to work well but every now and them it would just go 30 degrees off course and when I brought it back it would go the other way by a similar amount. It seemed worse if we were heading into current our motoring into a headwind or both.  I went through the commissioning process in port and underway but no great improvement. Last option was to check the AP drive chain for tightness. I found the drive chain between the AP drive and the steering gearbox was indeed loose. On our boat it is a PIA to tension this drive chain. There is a tensioning bolt to push the drive sideways but it is almost mission impossible to get tools onto this tensioning device. It also take two people to loosen and re-tension the AP drive securing bolts. After a lot of swearing - common on Australian boats- the job was done and today the AP performed perfectly during a 15nmile run motoring against a 1kn current and into a headwind. So if your AP is wandering check the chain drive tension. Loving it here in Fiji but the charting is reasonably poor with lots of scattered unchartered chunks of reef. 

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Wayne's World Members Profile Send Private Message Find Members Posts Add to Buddy List Admiral Joined: 18 July 2012 Location: Cruising Status: Offline Points: 1434	Post Options Post Reply Quote Wayne's World Report Post Thanks(0) Quote Reply Topic: Wandering autopilot Posted: 07 September 2025 at 06:28
	Our AP has not been holding course lately. It seemed to work well but every now and them it would just go 30 degrees off course and when I brought it back it would go the other way by a similar amount. It seemed worse if we were heading into current our motoring into a headwind or both. I went through the commissioning process in port and underway but no great improvement. Last option was to check the AP drive chain for tightness. I found the drive chain between the AP drive and the steering gearbox was indeed loose. On our boat it is a PIA to tension this drive chain. There is a tensioning bolt to push the drive sideways but it is almost mission impossible to get tools onto this tensioning device. It also take two people to loosen and re-tension the AP drive securing bolts. After a lot of swearing - common on Australian boats- the job was done and today the AP performed perfectly during a 15nmile run motoring against a 1kn current and into a headwind. So if your AP is wandering check the chain drive tension. Loving it here in Fiji but the charting is reasonably poor with lots of scattered unchartered chunks of reef.
	Wayne W Cruising, currently in the Pacific until the end of 2026.

Black Diamond Members Profile Send Private Message Find Members Posts Add to Buddy List Admiral Joined: 24 October 2015 Location: Newport, RI, US Status: Offline Points: 1275	Post Options Post Reply Quote Black Diamond Report Post Thanks(0) Quote Reply Posted: 07 September 2025 at 11:17
	Is this different from the typical XTE problem with following a track? In other words, its common for both Raymarine and B&G autohelms to try to get back to a line in "dramatic" fashion if not on course. The solution has always been to hit "restart XTE" and create a new line to target. I see this more in "track" mode than in "auto".
	Rick S/V Black Diamond Hanse 575 Build #192, Hull# 161 Newport, RI

Wayne's World Members Profile Send Private Message Find Members Posts Add to Buddy List Admiral Joined: 18 July 2012 Location: Cruising Status: Offline Points: 1434	Post Options Post Reply Quote Wayne's World Report Post Thanks(0) Quote Reply Posted: 07 September 2025 at 23:41
	Hey Rick, We normally run the AP in the Auto mode which means it travels on a set compass bearing. The MFD shows the XTE but the AP is not actively navigating to a WP. In Nav (tracking) mode the AP navigates to a WP and it should alter the course to take into account current etc which is taking the boat off this course. You are right in Nav mode if you "dodge" and then the AP will set a sometime dramatic course change to get back on the original course. We don't use the AP in Nav (tracking) mode only in Auto mode. My wandering problem was (I think) caused by the loose drive chain. Time will tell. I had to tighten this chain back in 2020 when about 500nm west of Cape Verde Islands with about 1000nm to run to Barbados. It was a lot more challenging to make the chain adjustment when underway. Had a good LED torch get completely crushed when it slid into the chains/gears when the boat rolled in a swell. Not sure how I didn't loose the odd finger. The chain was so loose at that stage that it was occasionally jumping a cog which I could feel at the helm.
	Wayne W Cruising, currently in the Pacific until the end of 2026.

Black Diamond Members Profile Send Private Message Find Members Posts Add to Buddy List Admiral Joined: 24 October 2015 Location: Newport, RI, US Status: Offline Points: 1275	Post Options Post Reply Quote Black Diamond Report Post Thanks(0) Quote Reply Posted: 07 September 2025 at 23:47
	Ouch Watch your fingers. Not sure I’d have tried that. I also never use tracking mode, just auto. How is it that the chain caused this?
	Rick S/V Black Diamond Hanse 575 Build #192, Hull# 161 Newport, RI

Wayne's World Members Profile Send Private Message Find Members Posts Add to Buddy List Admiral Joined: 18 July 2012 Location: Cruising Status: Offline Points: 1434	Post Options Post Reply Quote Wayne's World Report Post Thanks(0) Quote Reply Posted: 08 September 2025 at 00:06
	Rick, The problem in 2020 appeared to be caused by the fact that the AP drive motor was mounted with rubber grommets around the mounting bolts, to I gather reduce vibration. These grommets over time fell apart and allowed the drive motor to move towards the gear box sprocket making the chain loose - very loose in this case. This time it seems the torque of the drive motor, over time, had pulled the drive motor closer to the sprocket although the bolts were still fairly tight. When I checked the chain there was a noticeable droop in the chain of maybe 10-15mm. In 2020 with a 1,000nm still to go it was a case of had to do something. We ended up locking the steering and turned the AP off to stop any chain/sprocket movement whilst the work was done. Hope you got some summer cruising this season.
	Wayne W Cruising, currently in the Pacific until the end of 2026.

Black Diamond Members Profile Send Private Message Find Members Posts Add to Buddy List Admiral Joined: 24 October 2015 Location: Newport, RI, US Status: Offline Points: 1275	Post Options Post Reply Quote Black Diamond Report Post Thanks(0) Quote Reply Posted: 08 September 2025 at 01:02
	Nice detective work.. Beyond my diagnostic skills...
	Rick S/V Black Diamond Hanse 575 Build #192, Hull# 161 Newport, RI

Mainer Members Profile Send Private Message Find Members Posts Add to Buddy List Lieutenant Commander Joined: 05 January 2023 Location: Maine Status: Offline Points: 59	Post Options Post Reply Quote Mainer Report Post Thanks(0) Quote Reply Posted: 08 September 2025 at 12:20
	Hi Wayne, We had similar problems while sailing off the coast of Nova Scotia last year -- noticed a clunking/clicking noise while underway and was able to fix it but crawling into the bowels of the boat and tightening the bolts that hold the autopilot motor in place. Looking again last week I noticed that at least one of the rubber grommets has cracked. When you fixed your system did you keep the grommets or dispense with them? -Mainer

Pzucchel Members Profile Send Private Message Find Members Posts Add to Buddy List Rear Admiral Joined: 13 March 2020 Location: floating Status: Offline Points: 659	Post Options Post Reply Quote Pzucchel Report Post Thanks(0) Quote Reply Posted: 08 September 2025 at 20:48
	I have a long-standing love affair with my autopilot, jeffy. I have destroyed three lewmar, too, so I have some experience on the way it works . A lose chain of 10mm cannot be the origin of the problem, because the AP computer uses the information on the actual rudder angle and the (kalman) filtering is capable of dealing with large gaps in the actuation of the rudder. Are you sure your don't have any connectivity problem with the angular rudder sensor ? or maybe the sensor is noisy? some cabling issues ?I bet that the problem is there. As a side comment , since I am using the Jefa driver there is no evidence of the chain getting loose in years. I am surprised of hearing about rubber grommets: we are talking of extreme forces here , you can't move the rudder if the autopilot is not perfectly rigid with the boat ...am I missing something ? additional comment: I wouldn't trust a chain that is 10mm loose and an autopilot on rubber fixations. it can happen that the teeth of the pinion don't exactly match the links of the chain , and the chain would skip out of the pinion. it happened to me in an Atlantic crossing , and to prevent losing the AP I invented while sailing a rubber tube guide around the pinion that prevented the chain to jump out . not only it worked up to the arrival , but it's still there! said this , it happened only because the lewmar autopilot flange had started to fail ...Jefa is a as solid as a rock. Edited by Pzucchel - 08 September 2025 at 20:58
	Hanse588#55

Wayne's World Members Profile Send Private Message Find Members Posts Add to Buddy List Admiral Joined: 18 July 2012 Location: Cruising Status: Offline Points: 1434	Post Options Post Reply Quote Wayne's World Report Post Thanks(0) Quote Reply Posted: 08 September 2025 at 21:54
	Mainer, I left what was left of the grommets but there is not much left. Pzucchel, I tried everything I could with the AP settings before diving into the bowels of the steering flat but tightening the drive chain was the only thing that fixed the issue. We will soon see when we do some longer crossings. Destroying 3 AP - that must be a record!
	Wayne W Cruising, currently in the Pacific until the end of 2026.

Pzucchel Members Profile Send Private Message Find Members Posts Add to Buddy List Rear Admiral Joined: 13 March 2020 Location: floating Status: Offline Points: 659	Post Options Post Reply Quote Pzucchel Report Post Thanks(0) Quote Reply Posted: 08 September 2025 at 23:34
	I have a 588...they supplied them for years with an autopilot designed for a 40ft! finally they went back to the original Jefa , the one of the 575....i still can't understand how a 10mm slack can introduce à 30 degrees steering. Do you have an angular sensor on the rudder ?
	Hanse588#55



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