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Auto-pilot clutch slips under load to portside

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Category: Hints and Tips
Forum Name: 461 / 470
Forum Description: 461 / 470 Hints and Tips
Printed Date: 16 August 2022 at 04:56
Software Version: Web Wiz Forums 12.01 -

Topic: Auto-pilot clutch slips under load to portside
Posted By: psousa
Subject: Auto-pilot clutch slips under load to portside
Date Posted: 31 January 2022 at 17:24
Hi there!
My Jefa autopilot clutch fails when I pull the rudder wheel to port with my hands while the autopilot is engaged. It slips. Before this manual test, I realise this failure few times already when sailing close haul with 15/16 knots winds. The pressure over the rudder increase and the clutch starts failing. The system keeps trying to lock the rudder and eventually do it again when the boat gets into the wind, obviously reducing the pressure over the rudder.
This happens only to one side. To the other one the clutch holds pretty well.

Contacted Jefa and they ask me to do a test: to connect the clutch directly to the battery and try to pull the wheel by hand. Obviously they are trying to exclude the simrad autopilot computer from the equation, but before doing it I would like to ask you guys if you ever had such a problem and what are your thoughts about it. Is it possible to be an autopilot computer issue? Isn't the clutch a on/off only feature?

Posted By: JonB
Date Posted: 01 February 2022 at 22:08

My old Raymarine auto pilot had Alzheimer's in that it would suddenly let go with 'no drive' warning, I took the motor off to test the clutch, all good and yes its either engaged with pins or its not, so it can't slip. Thinking that it may be an issue between the fluxgate and the compass within the unit I tested the fluxgate. Deciding I didn't really know whether my findings would tell me anything I could understand and having upgraded the E series plotters to Axioms I opted to replace the auto too.  The ACU 200 was fitted and off I went only for it to fishtail the boat until we nearly gybed. I undertook several tests and once again it opted to, under engine (little wind), follow a search pattern without being asked to.

It was a struggle to get Raymarine to accept anything other than a limpware (user) issue, but eventually they sent over an Engineer who came and inspected with the Engineer who fitted it. When the auto pilot was asked to steer +10degrees and the helm was held to simulate weather helm, they were surprised that 15amps was called for by the Jeffa motor, bearing in mind it is protected with a 40amp fuse. They've since changed the unit for an ACU 400 which I assume handles the amperage better and once installed and the boats back in the water we'll be testing again.

Check the rudder sensor, probably by disconnecting it and see if it's the same both sides or cures the problem. You could have a similar issue in that the amperage being asked by the motor exceeds that of the unit fitted.

Jon B

Posted By: psousa
Date Posted: 03 February 2022 at 11:14
Regarding the amp demand for Jefa 12v sprocket drive unit (I guess the one you have), there is a graph which clearly shows it can demand up to 16amps when under weather conditions:" rel="nofollow -

My boat is equipped with a simrad ac42 autopilot computer. According to the manual, it can supply:
AC42: ....................30 A continuous, 50 A for 1 sec. peak

More, the issue is happening when pushing the wheel to portside only (doesn't happen when pushing the wheel to SB), so I guess it's not a power delivery issue.

I'll give a closer look ate compass and the rudder feedback when back to the boat.

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