P70 Autopilot veers off course

[Scrabble]

Note: This is a continuation of another thread as I think I have narrowed the issue down. https://www.cruisersforum.com/forums....html#poststop

My Raymarine AP has started veering off course after a software update. After several days of recalibrating I think it may be due to the boat being ‘knocked’ off course. Yesterday, I had a 4hr run (under motor) in calm seas and the autopilot work fine for about 2 hours when it suddenly turn to Stb (always Stb) and I quickly disengaged. Now the rudder indicator shows about 10deg port when sailing straight. I adjusted the offset to compensate and continued on. When nearing my destination an overpowered gin palace blasted past our port side and knocked us around significantly. The AP immediately started to veer to Stb (about 20deg offset). I have become adept and doing a dockside reset at sea so quickly fixed it before entering the port.

To me, it seems to be very coincidental that the AP failed when hit by a ‘rogue wave’. Has anyone ever experienced this. I’m keen to get this sorted as I have a 18hr crossing coming up this week.

Cheers

PS. No problems under standby

[donradcliffe]

The problem could well be loose rudder indicator.

[Scrabble]

Originally Posted by donradcliffe

The problem could well be loose rudder indicator.

I have just checked the rudder indicator and everything seems fine. I did, however, notice that the woodruff key locking the main rudder arm to the rudder shaft had fallen out (although the two channels were still aligned). I also found that a storage box was leaning heavily on the base of the rudder shaft where a large square clamp is fitted.

I am hoping that the combination of random resistance and a missing woodruff key was causing the misalignment. This could also explain the occurrence of the passing boat wash. The sudden pressure on the rudder twisted it in the rudder arm. The fact that it was still aligned when I checked it could be as I run the dockwizard and it straightens everything up again! Wishful thinking maybe?

I have now removed the offending box and reseated the key. I will be sailing again tomorrow and will let you know if it is a success.

Cheers

[more]

Manualy calibrate rudder gain and acceleration limit

[donradcliffe]

I now think the problem isn't the autopilot, it is the rudder shaft shifting under stress. The shifting could be due to the missing key, or it could be due to the rudder body turning on its shaft. I'd tie off the wheel, go over the side and try to push the rudder over.

[Scrabble]

To close this out - it was the quadrant that was slipping on the rudder shaft because the woodruff key had fallen out. Every time I ran the dockside wizard it would push it back into place. Woodruff key is reseated and everything now seems fine. Thanks for the tips.

[donradcliffe]

That key is really mission critical. Hope your fix made sure it would never fall out again.

[Pete7]

And carry a spare