Autopilot Disengages Without Warning

[dawntreader]

I use an A9 series MFD and S2 Controller for my autopilot/navigation. I converted from the C80 series MFD setup over 2 years ago and have sailed more than 2,000 miles since the changeover. All works fine EXCEPT on maybe 6 occasions, at random intervals and times, the autopilot disengages to 'Standby'. No-one is near the controls to cause this problem and the last time it did it was whilst I was standing next to the wheel wondering why the land was on the 'wrong' side of the boat 

Anyone else experience this problem?

[Lyra]

I would check electrical connections and condition of wires - on many boats  the wiring is non-tinned and corrodes with time.
A momentary voltage drop (due to corroded wires and momentary high current consumption) or momentary voltage loss (due to a loose contact) may cause a reset to the system.

[JEN-et-ROSS]

I would agree with Lyra as I would assume all auto-pilot systems are designed to be 'fail-safe', so in the event of a power interruption, however brief, it would logically default to 'standby'.

[dawntreader]

Thanks for your replies. The installation of the new equipment was done by me and, where bespoke cabling was required, this was implemented with new cables. As this is a 'recent' installation and within the cabin I don't believe corrosion to be an issue. The cables were either 'out of the box' or new, tinned wires. I will go back through my logs and look at the times of the failures against hours used on autopilot to gather some statistical evidence. It should also be said that the failures have happened both when under motor and under sail so it is not necessarily a 'surge' from the alternator. The batteries are both only 2 years old too (a matched pair).

If there was a 'momentary' loss of voltage should I have seen other indicators - for example loss of settings on the chartplotter etc.?

Can I rule out a software glitch if the occurrence incidence is very low against hours used?

[JEN-et-ROSS]

Since you mentioned software, it's worth considering that more complex 3-axis/Autothrottle AP installations are constantly monitored for system errors.
Should an error occur a visual/audible warning is triggered and the system disengages.
The fault/error can be easily accessed, a bit like the simple 'fault code reader' you plug into your car, though in this case it's in-built.

Our AP system is truly ancient but yours is modern, I was wondering, since we pay so much for these pieces of technology, can a modern Marine AP store current and past faults and system errors in a similar fashion to be interrogated later? If so, the cause of these 'drop-outs' may be stored in the system..........Just a thought?

[dawntreader]

Since you mentioned software, it's worth considering that more complex 3-axis/Autothrottle AP installations are constantly monitored for system errors.
Should an error occur a visual/audible warning is triggered and the system disengages.
The fault/error can be easily accessed, a bit like the simple 'fault code reader' you plug into your car, though in this case it's in-built.

Our AP system is truly ancient but yours is modern, I was wondering, since we pay so much for these pieces of technology, can a modern Marine AP store current and past faults and system errors in a similar fashion to be interrogated later? If so, the cause of these 'drop-outs' may be stored in the system..........Just a thought?

I'm off the boat for a few weeks but I do know that the C80 I had previously did do a 'self diagnosis' so would expect similar (at the very least) for the updated MFD's . Something to play with over winter when I get back

Something else to ponder too: If the autopilot motor had a minor/intermittent fault would that then cause the software in the MFD to switch to 'Standby'? A bit too clever for it I think 

[Yngmar]

If there was a fault (i.e. a command sent to the motor doesn't result in the desired rudder movement being sensed), it would beep and show an error message. Disengaging silently is unusual, but could happen, e.g. if the standby button somehow got short-circuited or it receives a command to disengage from the network (modern units can be remotely engaged/disengaged, e.g. from the plotter).

[canuck]

My 2017 Bav 37C with Garmin autopilot had a similar problem and was always disengaging - usually I got an error message about "rudder out of calibration" or similar. Always happened at the most inopportune time!  The dealer replaced about everything, until in the end it was just the rudder position sensor that is bolted to the back of the Jeffe drive motor.  Put new sensor on (potentiometer) and all is now well.
Good luck with yours.