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Old 11-04-2021, 09:33   #1
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Boat Icon 100 degrees off

For some reason, my boat icon is at about 100 degrees off of our true course regardless of Heads-up or North-up.

You can see my Magnetic heading in green and GPS course in red. (mag is adjusted to true north). What could be causing my boat icon to be off by 100 degrees.

Some background, I am using OpenCPN on RPi4. I had a M-HAT2 but removed it when I installed a AIS transponder. When I check our AIS it shows the correct heading so that cause is eliminated.
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Old 11-04-2021, 23:49   #2
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Re: Boat Icon 100 degrees off

My guess:
You removed the HAT, but not the (driver-software). For the HAT must can set a correction value in order to get a correct heading. I think this correction is still in use although the HAT itself is gone.
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Old 12-04-2021, 01:55   #3
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Re: Boat Icon 100 degrees off

If you have flux gate compass, check it hasn't been dislodged and is positioned correctly (or hasn't had a big lump of ferrous metal placed beside it).
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Old 12-04-2021, 08:20   #4
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Re: Boat Icon 100 degrees off

Thanks, I will remote in and check the software. Reefmagnet, I was thinking the same thing and calibrated the Flux Gate compass so those should be fine. Thanks for the post.
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Old 12-04-2021, 11:59   #5
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Re: Boat Icon 100 degrees off

If your flux compass was wrong wouldn’t the magnetic heading (green) be wrong too? As the boat changes course does the difference remain about 100 degrees or does it vary with course? Were you are moving faster than approx 1kt when the picture at the top was taken?
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Old 12-04-2021, 13:58   #6
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Re: Boat Icon 100 degrees off

Aedan, the Green and Red vectors are true to my heading.
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Old 12-04-2021, 15:37   #7
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Re: Boat Icon 100 degrees off

Ok, next question: Is your data coming into OpenCpn as a NMEA0183 stream? If so can you capture some of it with the VDR plugin and post it here?
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Old 12-04-2021, 16:12   #8
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Re: Boat Icon 100 degrees off

I remoted into the RBPi and the boat is sitting still.
<GREEN>16:10:49 (TCP:10.10.10.01:10110) !AIVDM,1,1,,A,35NK5o`000G?jQ6KAERmFP;p0000,0*77<0x 0D><0x0A>
<GREEN>16:10:49 (TCP:10.10.10.01:10110) !AIVDM,1,1,,A,35NOVnP000G?nw4KA;kbN4=p0000,0*23<0x 0D><0x0A>
<GREEN>16:10:49 (TCP:10.10.10.01:10110) $HCHDG,5.7,,,,*40<0x0D><0x0A>
<GREEN>16:10:49 (TCP:10.10.10.01:10110) $IIHDG,5.70,,,,*7B<0x0D><0x0A>
<GREEN>16:10:49 (TCP:10.10.10.01:10110) $IIHDM,5.7,M*20<0x0D><0x0A>
<GREEN>16:10:49 (TCP:10.10.10.01:10110) $IIHDT,5.7,T*20<0x0D><0x0A>
<GREEN>16:10:49 (TCP:10.10.10.01:10110) $HCHDG,5.7,,,,*40<0x0D><0x0A>
<GREEN>16:10:49 (TCP:10.10.10.01:10110) $IIHDG,5.70,,,,*7B<0x0D><0x0A>
<GREEN>16:10:49 (TCP:10.10.10.01:10110) $IIHDM,5.7,M*20<0x0D><0x0A>
<GREEN>16:10:49 (TCP:10.10.10.01:10110) $IIHDT,5.7,T*20<0x0D><0x0A>
<GREEN>16:10:50 (TCP:10.10.10.01:10110) !AIVDM,1,1,,B,15NL;SPP00G?fW4KA`>9rwwP2<3t,0*30<0x 0D><0x0A>
<GREEN>16:10:50 (TCP:10.10.10.01:10110) $HCHDG,5.7,,,,*40<0x0D><0x0A>
<GREEN>16:10:50 (TCP:10.10.10.01:10110) $IIHDG,5.70,,,,*7B<0x0D><0x0A>
<GREEN>16:10:50 (TCP:10.10.10.01:10110) $IIHDM,5.7,M*20<0x0D><0x0A>
<GREEN>16:10:50 (TCP:10.10.10.01:10110) $IIHDT,5.7,T*20<0x0D><0x0A>
<GREEN>16:10:50 (TCP:10.10.10.01:10110) $HCHDG,5.7,,,,*40<0x0D><0x0A>
<GREEN>16:10:50 (TCP:10.10.10.01:10110) $IIHDG,5.70,,,,*7B<0x0D><0x0A>
<GREEN>16:10:50 (TCP:10.10.10.01:10110) $IIHDM,5.7,M*20<0x0D><0x0A>
<GREEN>16:10:50 (TCP:10.10.10.01:10110) $IIHDT,5.7,T*20<0x0D><0x0A>
<GREEN>16:10:50 (TCP:10.10.10.01:10110) $GNGLL,4739.99536,N,12223.53768,W,231048.00,A,A*6F <0x0D><0x0A>
<GREEN>16:10:50 (TCP:10.10.10.01:10110) $GPGGA,231046,4739.9954,N,12223.5377,W,1,6,3,18,M, 0,M,,*7E<0x0D><0x0A>
<GREEN>16:10:50 (TCP:10.10.10.01:10110) $GPGLL,4739.9954,N,12223.5377,W,161046.020,A*2E<0x 0D><0x0A>
<GREEN>16:10:50 (TCP:10.10.10.01:10110) $HCHDG,5.7,,,,*40<0x0D><0x0A>
<GREEN>16:10:50 (TCP:10.10.10.01:10110) $IIHDG,5.70,,,,*7B<0x0D><0x0A>
<GREEN>16:10:50 (TCP:10.10.10.01:10110) $IIHDM,5.7,M*20<0x0D><0x0A>
<GREEN>16:10:50 (TCP:10.10.10.01:10110) $IIHDT,5.7,T*20<0x0D><0x0A>
<GREEN>16:10:50 (TCP:10.10.10.01:10110) $HCHDG,5.7,,,,*40<0x0D><0x0A>
<GREEN>16:10:50 (TCP:10.10.10.01:10110) $IIHDG,5.70,,,,*7B<0x0D><0x0A>
<GREEN>16:10:50 (TCP:10.10.10.01:10110) $IIHDM,5.7,M*20<0x0D><0x0A>
<GREEN>16:10:50 (TCP:10.10.10.01:10110) $IIHDT,5.7,T*20<0x0D><0x0A>
<GREEN>16:10:50 (TCP:10.10.10.01:10110) $HCHDG,5.7,,,,*40<0x0D><0x0A>
<GREEN>16:10:50 (TCP:10.10.10.01:10110) $IIHDG,5.70,,,,*7B<0x0D><0x0A>
<GREEN>16:10:50 (TCP:10.10.10.01:10110) $IIHDM,5.7,M*20<0x0D><0x0A>
<GREEN>16:10:50 (TCP:10.10.10.01:10110) $IIHDT,5.7,T*20<0x0D><0x0A>
<GREEN>16:10:50 (TCP:10.10.10.01:10110) $GPGGA,231046,4739.9955,N,12223.5377,W,1,6,3,18,M, 0,M,,*7F<0x0D><0x0A>
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Old 12-04-2021, 21:45   #9
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Re: Boat Icon 100 degrees off

I found this adjustment from when I was using the HAT. Could this be causing the issue and if so, how do I get ride of the old calibration.
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Old 13-04-2021, 00:51   #10
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Re: Boat Icon 100 degrees off

That's useful but if you could get a VDR trace file I could try and replay it here to see if it's something within OpenCpn or something specific to your installation. If you could do that when the boat is moving and OpenCpn is displaying the problem that would let people help you more.



I note that your HDM and HDT messages are both reading 5.7, is that correct for your area, no magnetic declination or variation?


You have several different sources of heading information coming in, I'd suggest you use OpenCpn filtering to filter them all out except one, if the problem has then gone away add them back in one by one and see when the problem reoccurs.


Your IIHDG message has a value of 5.70, usually it's just sent to one decimal, unusual but unlikely to cause a problem. if it is causing a problem the above approach will point to it anyway.



You appear to be getting everything from II and HC twice per second, is that because you have selected a 0.5 second rate or something in your system is duplicating it? If possible slowing it down might make it easier to debug.
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Old 13-04-2021, 08:26   #11
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Re: Boat Icon 100 degrees off

Thanks Aedan,

I won't be out on the boat until this weekend. I will try to reduce the number of messages and frequency and see what happens.
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Old 13-04-2021, 10:08   #12
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Re: Boat Icon 100 degrees off

Count yourself lucky you can get to your boat, ours is 250km away and lockdown rules are in operation. Hopefully they’ll be eased soon.
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Old 20-04-2021, 14:50   #13
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Re: Boat Icon 100 degrees off

I was not able to get out on the water this last weekend but I did some testing by filtering out each message. It is clear that the bad information is coming from the magnetic heading. I put other compasses close by to see if there was interference but could not find anything significant.

My assumption is that the fluxgate compass is bad. I plan to pull this out and rotate to see what happens to the magnetic heading sentence.
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