NAVpilot 500 failed rudder test

[Brad Allan]

I recently bought a 2004 boat with dual helm stations and a NAVpilot 500. The previous owner said the autopilot worked until he replaced the head unit at the upper helm due to illegible LED readout. Now both head units look and read normally. Both heading readouts show proper heading, both units show proper rudder position. When put into auto mode from either station the unit doesn't show anything abnormal, it indicates auto mode, but the autopilot is not controlling the rudder at all. When in standby mode, if I read the manual correctly, I should be able to control the rudder with the left & right arrows, but nothing happens. Going into system setup, everything seems to progress properly until the "rudder test". When activating that it will turn the rudder all the way starboard, then only about 10 degrees back to the port, then display "rudder test failed". If I do a google search on this condition, it says most likely is air in the system. The boat turns fine in both directions from both helm stations. Can I bleed the autopilot pump separately from the helm stations? There is a junction block in the system after the point where the helm stations and the pump are plumbed together, and just before the rudder actuating cylinder. Do I bleed the pump there? See picture of the junction block.

 

[Johnny Electron]

The second station is connected in parallel so the entire system is bled as a system. Normally the best way to do that is have someone with a "power purge" come out and run all the air out of the system. If you are not having any serious issues steering the boat by hand, then I am not sure I buy the air theory. I think it is something else. While the NP500 is about 20 years old, it is a very good pilot.

1) Check the back of your control heads. There are two connections. They should either have two cables connected or a cable and a terminator. There should be no open connection or dust cap.
2) When you run the rudder test and it fails it will say why it fails. Exactly what does it say when it fails?

 

[Brad Allan]

Thanks for your reply Johnny. Next time I'm at the boat I'll run the test again and give you that info. I don't know if this is of any help in diagnosing: I tried to do a sea calibration (manual mode because it wouldn't steer the boat to port in automatic), and part way through the process, the message "rudder drive error" came up.

 

[Johnny Electron]

My guess is the rudder reference unit has worn out and it can't sense the rudder is moving properly. Try checking the RRU using this document.

 

[Brad Allan]

Thanks, I'll do that. However, it appears that the RRU is working properly because the rudder position indication on both autopilot head units looks to be accurate and consistent in both directions.

 

[Johnny Electron]

Need the rudder test results to move further. It should include the rudder speed, deadband and other infomation.

 

[Brad Allan]

Ok, thanks

 

[Brad Allan]

Hi. I'm back at this boat now and the first thing I see that isn't consistent with your description is that the head unit at the upper helm has one open connector, no terminator, no dust cap. The unit at the lower helm has two cables connected, I suppose one to the processor and one to the upper unit.

 

[Brad Allan]

Hi. I'm back at this boat now and the first thing I see that isn't consistent with your description is that the head unit at the upper helm has one open connector, no terminator, no dust cap. The unit at the lower helm has two cables connected, I suppose one to the processor and one to the upper unit.​

And here is the screen that comes up after the rudder test has failed - in addition to saying rudder test failed, it says "rudder drive error"

 

[Johnny Electron]

The head unit at the upper helm requires a termination on the open connector so that it has a valid bus. Right now that is open and can cause all sorts of problems.

 

[Brad Allan]

Thanks. I ordered one, should have it in a couple days. I'll let you know how it goes

 

[Brad Allan]

Hi. Success! I installed the terminator, ran through the dockside setup from the start, did an automatic compass calibration at sea trial and it's all working. There is one part of the dockside setup that is puzzling me though, the Adjust Rudder Reference Unit. When the helm is at center, and the AP shows center when in Standby I get into the Adjust Rudder Reference function and it indicates that the rudder is 14 deg to starboard. When I turn the helm to starboard lock it indicates 64 deg starboard. Turning to port lock it shows 27 deg port. When I try to set both locks at 31 deg it doesn't change these values. Any help here is appreciated.

 

[Johnny Electron]

The center of the RRU in the dockside setup is just a rough center. Once the pilot has been fully configured and passes the rudder test, one must take the pilot on the SeaTrial. During the Seatrial there is a "Set Center" that must be done to establish what I call the "Fine Center" that makes the boat go straight when the transducers and other drag is accounted for.

 

[Brad Allan]

Thanks. Did a successful rudder test, successful compass calibration during sea trial and set rudder center under way during sea trial. On the main screen in standby mode the rudder position shows 0 degrees when in fact the rudder is at 0 degrees. Then I go into the Dockside Setup / Adjust Rudder Reference Unit screen. As shown in the last photo, even though the rudder is centered, and it indicates centered on the main screen, it shows a rudder position of 14 degrees starboard in this screen. Then, as instructed I turn the helm to hardover starboard and it shows 64 degrees starboard. When I select the adjustable value for hardover starboard and change the value to 31 degrees and confirm, it does not change the indicated value in the line above where it shows 64 degrees

 

[Johnny Electron]

To be clear, once dockside and sea trial is done; one doesn't go back and start fiddling with the dockside settings again unless you wish to start completely over and do it all again. The RRU centering is based on resistance. The RRU can be tested using that troubleshooting document provided previously but you can also loosen the center lug/arm of the RRU and center it physically via resistance with a meter whenever your steering is in complete alignment. This would ensure that the RRU is center when your steering is at rough center. I personally don't recommend dialing in numbers greater than 30 for your port and starboard hard-over, regardless of the angle. Then I put the "Auto rudder limit" at 20 and the "Manual rudder limit" at 25 for every outboard RRU I ever install. It works great every time. one must ensure the helm is turned correct when doing Port/Starboard/center in the dockside.

 

[Brad Allan]

I did just that, removed the RRU arm and physically adjusted the potentiometer to match zero for a straight course. What I didn't understand before is that the angle value in that Adjust Rudder Reference Unit screen was not adjustable on the control unit.

Thank you very much for your expert advice with this, it's a very valuable service. I had two marine electronics professionals on my boat to figure out the autopilot issue. After spending nearly $1,000 between the two of them, the second one said I need a whole new system.

 

[Johnny Electron]

500 pilot is a good one. It sounds like you did a great job.