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Old 20-11-2010, 11:26   #1
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Weird Heading Data

Chapter 2.

I have now replaced the fluxgate compass on my nav system -- RL80CRC+, RL70CR+, S3 course computer, ST7000 pilot controller, etc.

I have checked what connections I can.

But I'm still getting the same intermittent fault with the heading. Sometimes the heading is 20 or 30 degrees off; sometimes 180 degrees off.

The autopilot functions normally -- it does not jerk around when the heading is off.

What can this possibly be? I don't understand what part of the system generates the system's opinion about the heading -- is it the course computer? The autopilot controller?

It seems I don't have a gyro after all. Maybe it makes sense to replace the course computer with the S3G with the built in rate gyro -- I probably need that anyway, and it would eliminate one more potential source of the problem.

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Old 20-11-2010, 12:15   #2

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Look for something that has been newly placed near the fluxgate sensor. We had a similar thing happen - our sensor is buried in a galley cabinet at the very center of the boat. My wife changed the drawer used to store silverware and the heading was messed up like you're seeing. Pulling the drawer out made it start to work again and verified the issue. It took a long time to figure it out though.

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Old 11-12-2010, 12:10   #3
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Does this happen when the vessel is in motion, or only when at rest?

If it is only happening at rest, I would suggest that perhaps your fluxgate compass is working just fine and feeding a correct heading into your autopilot, but that you are monitoring a heading generated by your GPS. When the vessel is stationary, this may well swing around randomly.
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Old 11-12-2010, 12:46   #4
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One of the things that I had found to give erratic data readings in my system is multiple intruments that repeat NMEA sentences into the network. I have cleaned this up by looking at ALL the sentences that each instrument generates and what sentences each repeats and then I have turned off the sentences that I do not need or that are redundant with other instuments. This cleaned up the data flying around, decreased the time used and gave me one rational NMEA talker for each sentence that I use.
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Old 11-12-2010, 13:12   #5

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Did you look around where the actual sensor is located - my suggestion from 11/20? I had the exact same problem with pretty much the exact same chartplotter, etc. I have a course computer too (although I think its a G3, not an S3).

Anything within about 3 feet of the sensor can cause exactly the effects you're seeing...
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Old 11-12-2010, 22:46   #6
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I have had this a few times and only discovered what it was about a month ago.
For some reason the gremlins had got into system setup and entered variation as 30 deg West.
We have 10 East here....
Adjust back to 10 E - all AOK.
Hope this helps.
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Old 12-12-2010, 07:29   #7
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Off the top of my head I seem to recall that the Raymarine S3G autopilot computer will use NMEA HDG first, then SeaTalk, then its own heading sensor. There's a possibility that, if you have some inexpensive after-market GPS, it is erroneously reporting GPS heading information ($GPHDT) as a magnetic compass heading ($HCHDG).

Since the autopilot is working correctly, it seems the display is what is confused. When you say the heading is off by 20-30 degrees, or sometimes 180, is it the chartplotter's display of heading info that's off, or is it the autopilot controller? We had a similar issue with our E-120, but after a firmware update it went away...

Of course, now the E-120 seems to lose a day or so when showing ETA on the current route (works fine for ETA in hours, but for time-of-day it gets confused - obviously a software glitch)...
Cap'n Jon (KB1HTW)
S/V Beausoleil -1979 Formosa 51 Ketch
"If it's gonna happen, it's gonna happen out there." - Captain Ron
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Old 12-12-2010, 07:45   #8
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My Robinson sometimes after long periods of not being used requires that I swing the boat to set the compass. There are instructions for the Robinson in the owner's manual. Check your manual, yours may have that type of problem and the fix is simple.

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Old 12-12-2010, 11:14   #9
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"Foggy"'s right-Raymarine has specific instructions in their Auto-Pilot manual on how to "swing" the compass. If you lack a copy, you can find one on their site. We had the same issue and ended up relocating the compass and "reswinging" it. Capt.Pat

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