Wandering A/P

Last time out my ComNav 2001 autopilot had a hard time intercepting a course. It would way undershoot after a waypoint, then never quite intercept the new course.


I've had zero issues with it before. Has anyone else had a similar experience and locate the problem?

If nothing else changed and it was working well in similar conditions before, I'd find the fluxgate compass and make sure nothing was inadvertently placed near it that would interfere with the magnetic heading.

Peter

What Peter said. We had a bow thruster installed over the winter. When the power to the bow thruster is on the Auto Pilot is off by 40 degrees. Auto Pilot compass is located right down by the thruster. Oh well. Surly both not be used at the same time.

It’s easy enough to check the compass next time you’re out. The automatic compass adjustment procedure is in the manual, and if there’s an issue it will let you know that you need to move or manually adjust the compass.
I did this yesterday, and it’s telling me I need to do just that. I’ll be looking for a compass adjuster to come in and help with it.
I’m just getting used to the garmin plotter and using waypoints and routes, so I don’t have a ton of feedback, but I did notice that going to a simple waypoint the pilot was spot on till I neared the waypoint, and then it got off course. Didn’t have much time to mess with it unfortunately, but I’m suspecting the compass issue may be at fault.

mvweebles said:

If nothing else changed and it was working well in similar conditions before, I'd find the fluxgate compass and make sure nothing was inadvertently placed near it that would interfere with the magnetic heading.

Peter

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This. It happened to me when we loaded up e tra food for our 4 month trip. I put a milk crate full of canned goods too close to the compass. Took me a few to realize what I did. Hope your solution is that easy.

Bmarler said:

I’m just getting used to the garmin plotter and using waypoints and routes, so I don’t have a ton of feedback, but I did notice that going to a simple waypoint the pilot was spot on till I neared the waypoint, and then it got off course. Didn’t have much time to mess with it unfortunately, but I’m suspecting the compass issue may be at fault.

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Certainly check the compass and possible interference, but if the issue is solely wandering as you near a waypoint, I'd also look at the A/P settings. There are three main settings to all A/Ps

1. Yaw (or XTE - Cross Track Error); or how far from the courseline before corrective action is taken.

2. Rudder - how much rudder to apply

3. Counter-rudder. How much counter-steer to apply to straigten the course after rudder-correction has been made.

From your brief description, guessing the issue is in the XTE/Yaw setting - the boat is allowed to get too far off the rhumbline which is fine until the angle closes-in at the waypoint, then it just takes too much to course-correct (Rudder is likely too low too).

These are just guesses. I can tell you from experience that adjusting an A/P is an exercise in restraint and patience. As the attached diagram from Comnav shows, if the boat is swinging/zig-zagging, reduce settings which is a bit counter-intuitive.

Good luck. Please update when you figure it out.

Peter

EDIT - on the third Comnav diagram - "Not enough rudder," they should also show the boat over-shooting the mark due to too little rudder, then slowly drifting to the trackline to next waypoint. In my experience, this is more common for 'too little rudder' than the scenario they show. But you have to play with it. Best is to have someone at the helm and you bury your head to observe the rudders being actuated. You will learn a lot, at least until the blood runs out of your brain....

15
Is this new issue in your same cruising grounds or are you moving North? We’ve found a few locations in AK create compass havoc so keep AP off Nav mode.

In addition to what Peter states in post #6 another setting than can affect acquiring the next course is arrival distance. This can be set in the plotter as well. Too small an arrival radius and the AP has to work too hard to make the turn then may overcorrect. It may not be able to recover from the overcorrect.

Sent from my SM-T500 using Trawler Forum mobile app

I'll take a look at and around the A/P compass. This thing has worked flawlessly for 3.5 years I've owned it. I did notice the stand-alone wet compass differs from the A/P compass by 20 degrees. I honestly don't know if that's new or not. I've not climbed into the bridge helm and compared them before.



The nav system is a Furuno NavNet 3D. It's been there for the past 2 years. No changes to it. Could it be the source of a ComNav 2001 A/P issue?

So, I examined everything at and around the rudders, the A/P drive components (servo, pump, feedback pot, etc) and find nothing to indicate an issue. I looked at the compass, and from what I can see it's unencumbered and free of any metal masses nearby.

I have maybe 2 possibilities:

1. I recently coiled up the GPS antenna wire coming from the AIS, and placed that coil right next to the A/P control head (behind the dash). Could that cause the sudden onset of wandering/inability to maintain course?
2. My Furuno AIS is screwed up. Last time out the Transmit light indicated it was working, but the thing wasn't receiving or displaying anything. The AIS antenna cable goes by the compass, maybe 1 foot away. I'd think the woven cable sheath/ground would prevent issues, but maybe not? If the AIS was constantly transmitting (hence no received signals) maybe that was messing with the compass?
Or something else I just thot of - maybe the A/P hydraulic pump is failing?

My ComNav was steering erratically when I bought the boat, went through a complete reset (I think they call it a dock reset) and that fixed it.

Juliet 15 said:

So, I examined everything at and around the rudders, the A/P drive components (servo, pump, feedback pot, etc) and find nothing to indicate an issue. I looked at the compass, and from what I can see it's unencumbered and free of any metal masses nearby.

I have maybe 2 possibilities:

1. I recently coiled up the GPS antenna wire coming from the AIS, and placed that coil right next to the A/P control head (behind the dash). Could that cause the sudden onset of wandering/inability to maintain course?
2. My Furuno AIS is screwed up. Last time out the Transmit light indicated it was working, but the thing wasn't receiving or displaying anything. The AIS antenna cable goes by the compass, maybe 1 foot away. I'd think the woven cable sheath/ground would prevent issues, but maybe not? If the AIS was constantly transmitting (hence no received signals) maybe that was messing with the compass?
Or something else I just thot of - maybe the A/P hydraulic pump is failing?

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Easy enough to move them and find out. That would be number one on my list of things to try.

Comnav offers outstanding tech service.

Call them. They are in BC. They have seen it all & should help you quickly troubleshoot.

Satish used to be the guru - I have not needed help for 10 years, so he might still be there or moved along.

Have you done an update on your software recently? Had all the Raymarine replaced with Simrad when we bought our boat except the drive arm of the AP. Did replace the AP computer. Things ran just fine for months and many miles. Every time we turn it on it tells use available updates. System gets internet from known WiFi and our phones or IPads so stuff updates if it sees updates are available and we give permission. After one such update AP worked poorly. Initially wouldn’t work at all. With a reboot would work but only in one mode (No Drift). Then just had the AP computer do it’s recalibration bit and subsequently it worked just fine in all modes.
Don’t know your system but do see some mix of brands. Perhaps it’s on the software side not hardware. Some updates don’t translate well through mixed systems so require recalibration as well as a new search for devices in the network.

When in doubt look at the things you did last! Coiling the wire, putting a new scuba cylinder in the bow, or even rerouting the windlass cables too near the magnetic compass. When I power up the windlass I sometimes locked up the compass and my autopilot steered in circles, so I put it in standby mode when anchoring up. Anchor down either doesn't do it, or I have never noticed it because I am anchored

Check the check valves in the helms

Rubber Duck, which valves are you referring to?

There are check valves built into the helm pumps. Otherwise, when you turn one helm, path of least resistance would be to turn the other steering wheel vs the rudder. In the early days of hydraulic steering these were fit on the lines, not in the helm pump assembly.

To my knowledge, they are not serviceable without dissambly. I have never known one to fail but I suppose it's possible. Even more unlikely would be for both to fail simultaneously. If the check valve(s) died, the non-use steering wheel would turn instead of the rudder. Pretty sure the boat would be unusable.

Peter

Thx. It's worth checking. It seemed (but I'm not certain) to have a harder time intercepting to starboard vs intercepting courses to port. Additionally, the way this sytem is designed, when the A/P is engaged both helm stations stop working. You can turn the helm but the rudders don't respond; the autopilot has total control. So if there was a valve failure I wouldn't see one wheel inapprpriately turning (path of least resistance).

As for your AIS, if you've got the FA-50 then you'll probably need to do an update on it. The one connected to my four MFD12 units needed updating. You need to use a Windows PC connected into the same network as the FA-50. The issue was the firmware in them needs to be updated to reflect the changes of GPS satellites in the 20 years since it was first programmed. The update it quick to install. If you haven't done an update on it any time in the past two years then you'll likely NEED to do it.

For us the symptom was others couldn't see our AIS data. We could see theirs without issue. The FA-50 requires it's own GPS antenna and if it can't get a proper signal then it will not transmit.

I recently replaced two of the four MFD12 plotters with two TZT16F plotters. The TZT16F requires a slightly hole but otherwise fits perfectly in the same spot.

mvweebles said:

Certainly check the compass and possible interference, but if the issue is solely wandering as you near a waypoint, I'd also look at the A/P settings. There are three main settings to all A/Ps

1. Yaw (or XTE - Cross Track Error); or how far from the courseline before corrective action is taken.

2. Rudder - how much rudder to apply

3. Counter-rudder. How much counter-steer to apply to straigten the course after rudder-correction has been made.

From your brief description, guessing the issue is in the XTE/Yaw setting - the boat is allowed to get too far off the rhumbline which is fine until the angle closes-in at the waypoint, then it just takes too much to course-correct (Rudder is likely too low too).

These are just guesses. I can tell you from experience that adjusting an A/P is an exercise in restraint and patience. As the attached diagram from Comnav shows, if the boat is swinging/zig-zagging, reduce settings which is a bit counter-intuitive.

Good luck. Please update when you figure it out.

Peter

EDIT - on the third Comnav diagram - "Not enough rudder," they should also show the boat over-shooting the mark due to too little rudder, then slowly drifting to the trackline to next waypoint. In my experience, this is more common for 'too little rudder' than the scenario they show. But you have to play with it. Best is to have someone at the helm and you bury your head to observe the rudders being actuated. You will learn a lot, at least until the blood runs out of your brain....
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I’ve had a little time to try to resolve some of the problems I was having, maybe there’s something the OP can gain from my experience as well.
The main reason mine was wandering as I neared the waypoint was due to a cross track error setting. You can have regular or reverse depending on how the plotter calculates it. Mine was backwards. I thought I had it set right but I didn’t have enough distance on the first waypoint’s I tried to really see how it was acting. It really easy to change this setting, I can see it getting changed while poking around at the buttons if you’re not careful. Comnav is great about making these changes easy to do, but there’s no “are you sure” prompt. Changes happen immediately.
From there it was playing with rudder and counter rudder. I put the fast and slow settings to be the same as my boat is never really fast enough to have different settings for those. Yaw is as low as it goes without setting at zero. It wanders a tiny bit, but not bad.
To the OP, it might be worth checking to see if changing from fast to slow, or vice versa helps. Again, that choice is super easy to change, maybe without realizing it.
My third issue is compass related, I don’t have a solution for that one yet. The compass obviously needs moved. It’s about an inch and a half away from the main wiring chase to the pilothouse. Every time a load is turned off or on I get compass deviation. Not sure yet where i might move it to that will be clear enough as there’s stuff everywhere that will interfere.
But at least the autopilot is stable if nobody uses any power. Obviously it can’t stay like this, but at least I understand why it does the things it does.

Bmarler said:

My third issue is compass related, I don’t have a solution for that one yet. The compass obviously needs moved. It’s about an inch and a half away from the main wiring chase to the pilothouse. Every time a load is turned off or on I get compass deviation. Not sure yet where i might move it to that will be clear enough as there’s stuff everywhere that will interfere.

But at least the autopilot is stable if nobody uses any power. Obviously it can’t stay like this, but at least I understand why it does the things it does.

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I switched to using an SCX-20 satellite compass up on the mast of our EB47 and have been very pleased with the performance. The placement of it up there eliminated the problems of inconsistent readings I was getting from a PG700 mounted down at the waterline in a forward cabin.

If moving yours around doesn't work out, using a different sensor like the SCX is worth considering (just not cheap).

wkearney99 said:

I switched to using an SCX-20 satellite compass up on the mast of our EB47 and have been very pleased with the performance. The placement of it up there eliminated the problems of inconsistent readings I was getting from a PG700 mounted down at the waterline in a forward cabin.

If moving yours around doesn't work out, using a different sensor like the SCX is worth considering (just not cheap).

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That’s interesting. I will look into that. The comnav pilots will accept a few different compasses, I’ll check to see if there’s something compatible. I was thinking of going lower/more forward, but maybe higher with sat compass is better.

To the OP, I also forgot to mention, I adjusted the transition distance to 250 feet. My comnav responds perfectly to that.

I should point out that the SCX-20 is an NMEA-2000 device and I'm not sure your setup would take the values from it. Sorry, I didn't check on that first, and reading their online materials indicates it only supports NMEA-0183 and even then rudder is not mentioned. I gather it's designed to use only it's own compass input.

If it did there are "ways" to get N2K data back out to 0183 but you're jumping through hoops and introducing more complications. By the time you did that you'd probably be well on your way toward what the cost of a whole different autopilot setup would cost.