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Old 23-05-2016, 14:56   #1
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Garmin GHP 12 Autopilot - Rudder calibration is drifting

I've got a GHP12 autopilot with a GHC10 display and a Garmin Class A drive unit (model A1-0739). While sailing the rudder position loses calibration. Sometimes it thinks that the rudder is hard over when in reality it is dead center. Result is that it won't steer because "Rudder Near Limit". I can quickly enter the dealer autopilot configuration and recalibrate the center position, but it will still give "Near Limit" warning. Then a couple hours later I'll try engaging it again and it will work fine for a while. Go figure.

The Class A drive unit has a built in rudder feedback sensor. It's not an external sensor system that I understand most autopilots have. My guess is that this sensor is going bad, though the unit is only a few years old.

Garmin didn't have a clue and told me to add an external GRF10 position indicator or send the Drive Unit in for repair. Since we are cruising and currently in the Dominican Republic, that does me no good.

Has anyone else encountered this?


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Old 23-05-2016, 19:40   #2
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Re: Garmin GHP 12 Autopilot - Rudder calibration is drifting

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Originally Posted by MondayNever View Post
I've got a GHP12 autopilot with a GHC10 display and a Garmin Class A drive unit (model A1-0739). While sailing the rudder position loses calibration. Sometimes it thinks that the rudder is hard over when in reality it is dead center. Result is that it won't steer because "Rudder Near Limit". I can quickly enter the dealer autopilot configuration and recalibrate the center position, but it will still give "Near Limit" warning. Then a couple hours later I'll try engaging it again and it will work fine for a while. Go figure.

The Class A drive unit has a built in rudder feedback sensor. It's not an external sensor system that I understand most autopilots have. My guess is that this sensor is going bad, though the unit is only a few years old.

Garmin didn't have a clue and told me to add an external GRF10 position indicator or send the Drive Unit in for repair. Since we are cruising and currently in the Dominican Republic, that does me no good.

Has anyone else encountered this?


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Love your vids!

If the cost is an issue and you have insurance, they might cover overnighting the autopilot in for repair... its a safety issue. Talk to them and see if you can overnight it and overnight it back. At worse, you get stuck drinking $2 beers for two weeks!
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Old 23-05-2016, 19:59   #3
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Garmin GHP 12 Autopilot - Rudder calibration is drifting

It's not so much a cost thing as a time thing. As much as I love gigantic $2 Presidentes, we're planning to cross to Mayaguana in the next few days and from there we won't be in the same anchorage for more than a couple days until...ohhhh... August? Our aversion to slowing down is way greater than our dislike of hand steering.


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Old 24-05-2016, 01:11   #4
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Re: Garmin GHP 12 Autopilot - Rudder calibration is drifting

try bleeding the system? the rudder feedback would be based on fluid movent within the pump I would guess. maybe air in it.
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Old 24-05-2016, 06:57   #5
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Re: Garmin GHP 12 Autopilot - Rudder calibration is drifting

As far as I can tell it's a totally closed system that is not designed to be disassembled. But I'll admit that your idea hadn't even occurred to me as a possibility. Thanks.


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Old 24-05-2016, 07:40   #6
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Re: Garmin GHP 12 Autopilot - Rudder calibration is drifting

The Garmin Class A liner drive unit is built by Jefa. Maybe ask them rather than Garmin?

http://www.jefa.com/
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Old 24-05-2016, 08:34   #7
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Re: Garmin GHP 12 Autopilot - Rudder calibration is drifting

Love your videos too. I was hoping you guys make it up to Tampa Bay and we can show you a good time.. Good luck on the autopilot. I would suggest to see what is happening as you are sitting at the dock an engage the autopilot and have someone (your lovely wife) rock the boat while you are down below to see what the power unit is doing. Or if you are on the hook just let the boat swing. Good luck
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Old 24-05-2016, 09:33   #8
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Re: Garmin GHP 12 Autopilot - Rudder calibration is drifting

I have a similar Garmin system that I installed last month, although I connected it to a B&G class A drive from my previous autopilot with its associated B&G rudder reference unit. After calibrating the Garmin autopilot using the dockside and sea trial wizards, it worked fine for a few hours, but then I encountered the same problem you did: "Rudder near limit." The rudder was actually near its center position. I found that if I simply clicked on "ok," the autopilot continued on course.

I have since redone the calibration wizards and the problem has not recurred, but I have tested it for only one afternoon of sailing. Because I often sail single-handed, a reliable autopilot is essential for me. Please keep me posted on what you discover about the problem.
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Old 24-05-2016, 18:52   #9
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Re: Garmin GHP 12 Autopilot - Rudder calibration is drifting

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As far as I can tell it's a totally closed system that is not designed to be disassembled. But I'll admit that your idea hadn't even occurred to me as a possibility. Thanks.


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yah never mind, was assuming a hydraulic steering system. that's the only garmin systems I have put in.
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Old 24-05-2016, 20:20   #10
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Re: Garmin GHP 12 Autopilot - Rudder calibration is drifting

I have found that the latest garmin update seems to not behave as well when your drive unit is not perfectly aligned to your steering system.

On our boat, we have a jefa direct drive unit coupled to the GHP12. Because of the way we needed to physically install the drive to fit in the space allotted we needed to offset the drive unit a few degrees. So, hard over in one direction allows the rudder to travel just a little bit further than hard over on the other direction. With the old software version we did not have a problem programming the rudder center position but in the new version we needed to go through the dock and sea wizard and afterward manually set the center position of the rudder in one of the menu's.

I think its a software defect.
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Old 25-05-2016, 04:52   #11
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Re: Garmin GHP 12 Autopilot - Rudder calibration is drifting

Hi Crew,

While I must confess I have no ideas to help you out I did want to take a moment and say I love your videos as well.. One of your subscribers here!

We too are in Tampa Bay and if you ever hit the Gulf (unlikely I know) we would love to treat you two, and whatever guests you may have on board, to dinner and drinks!
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Old 25-05-2016, 08:38   #12
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Re: Garmin GHP 12 Autopilot - Rudder calibration is drifting

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Originally Posted by fallingeggs View Post
The Garmin Class A liner drive unit is built by Jefa. Maybe ask them rather than Garmin?

http://www.jefa.com/

Thanks for this. Unfortunately it looks like their drive unit is adapted for the Garmin system by the addition of a Garmin-made rudder feedback sensor - the very component that's giving me problems.

Thanks to everyone else as well. It's looking like I'm stuffed until we get back to the States. Good thing we picked up another crew member last night! The two ons,two offs were getting tiring.

And if we're ever in Tampa, we'll let you guys know!




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Old 25-05-2016, 08:40   #13
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Re: Garmin GHP 12 Autopilot - Rudder calibration is drifting

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Originally Posted by zboss View Post
I have found that the latest garmin update seems to not behave as well when your drive unit is not perfectly aligned to your steering system.

On our boat, we have a jefa direct drive unit coupled to the GHP12. Because of the way we needed to physically install the drive to fit in the space allotted we needed to offset the drive unit a few degrees. So, hard over in one direction allows the rudder to travel just a little bit further than hard over on the other direction. With the old software version we did not have a problem programming the rudder center position but in the new version we needed to go through the dock and sea wizard and afterward manually set the center position of the rudder in one of the menu's.

I think its a software defect.

We actually have the same problem with the slightly different range of travel and the need to set center manually. Unfortunately I don't think that's related to the drifting calibration problem.


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Old 02-06-2016, 04:16   #14
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Re: Garmin GHP 12 Autopilot - Rudder calibration is drifting

I have pulled mine apart a few times, it got wet in an offshore race after we took on some water. They are not very happy about getting wet but to it's credit the unit is still going strong 3 years and many miles later.
I replaced the rudder reference unit last year it is pretty much the same as one of these 534B1103JC8872 - VISHAY - Rotary Potentiometer, Wirewound, 534 Series, 10 kohm, Linear, 10 Turns, 2 W, Panel | element14 New Zealand
Just un-solder the existing one and replace.
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Old 12-06-2016, 10:08   #15
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Re: Garmin GHP 12 Autopilot - Rudder calibration is drifting

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I have pulled mine apart a few times, it got wet in an offshore race after we took on some water. They are not very happy about getting wet but to it's credit the unit is still going strong 3 years and many miles later.

I replaced the rudder reference unit last year it is pretty much the same as one of these 534B1103JC8872 - VISHAY - Rotary Potentiometer, Wirewound, 534 Series, 10 kohm, Linear, 10 Turns, 2 W, Panel | element14 New Zealand

Just un-solder the existing one and replace.

Great info, thank you!

I'm guessing it's tucked inside that cylindrical housing on the drive unit?


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