NavPilot 511 heading and rudder angle off by ~25 degrees

[spindrifter]

After a day of fishing with the NavPilot 511 autopilot working normally, it stopped working apparently due to a heading issue.

I first noticed a deviation alarm (autopilot not able to keep commanded course) and that the rudder angle indicator on the autopilot controller was stuck around 21 deg to starboard. (Normal range is 30-34 deg each side). The autopilot was apparently not able to turn to starboard sufficiently to keep course and the rudder angle indicator stayed around 21-24 deg to starboard.

Then there was a different alarm, something like “Heading (or rudder) sensor drift” but I can’t remember exactly or find it in the manual. I checked the rudder angle sensor arm that connects the sensor to the rudder and it was still in place (I replaced it about a month ago).

While driving manually to an anchorage, I ran through the test menu, but nothing worked. The autopilot read about 21 degrees to starboard when the rudder was centered while driving. This is when I noticed that the NavPilot’s heading readout was consistently about 20-25 deg to starboard of both the GPS and the chart plotter’s internal GPS. All are in degrees magnetic. (When the standalone GPS and my chart plotter read a course/heading of ~ 000 deg M, the autopilot read about 025 deg M.

This seems to be the issue but I can’t figure how to reset or recalibrate the autopilot.

After anchoring and shutting down the autopilot and restarting it this morning, the rudder angle sensor seems to be back in order (the port/starboard rudder angles are about 31 deg either side). I’m about to head to town and I’ll report what I experience otw back.

 

[Johnny Electron]

It would be good to know your history with this older pilot. Did you pick this up used or has it been working on the boat for many years etc?
It almosts sounds like the termination plug behind the control head is missing. I have see these pilots work for many years and suddenly lose their mind because the original installer forgot to put it on. Open communication buses are very unpredictable. The back of the control head should have two cables (one going to a second display) or a cable and a termination plug. No open port. No dust cap.

 

[spindrifter]

Both ports are filled, one cable to the CPU or whatever it’s called and one to the other control unit in the stern. It came with the boat, I’ve had it for four years and it has mostly worked well but I think it’s showing it’s age and probably needs to be replaced.

When I ran the heading sensor test again I did notice one of the test prompts said “NG” which I assume is no good? Not sure if the heading sensor or however this thing gets heading info can be replaced or recalibrated or fixed…

After “resting” for a while, the autopilot works for maybe half an hour before slowly drifting out of whack again. Once it does this, a simple power reset doesn’t fix the problem; it has to “rest” again.

 

[Johnny Electron]

The Navpilot 500 series stopped selling around 2009 most are definitely showing their age. You might check your control at the stern for the termination. Seriously, I had a customer run for 5 years without one until he ran into problems and we found it missing. The fix was to put the correct termination in place. You are correct that NG = No Good. After checking for the termination, I would find out the details of exactly what it is calling out as NG because that is very important.