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Old 11-08-2018, 10:53   #1
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Why is my chart plotter pointing wrong?

I had someone come in and splice in one of my electronic cables (NMEA or something like that). Ever since, the boat icon points about 60 to 120 degrees to the left of the point of sail. Any thoughts? It’s pissing me off

Also, I was on the vessel yesterday and a few times, at slow speeds, the chart plotter said "position fix lost". Could that have something to do with it?

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I’m also looking to upgrade my chart plotter and also my wind direction ST60 unit. Anyone know someone around NJ, NY, or CT that does a good job?

Thanks!!
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Old 11-08-2018, 11:42   #2
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Re: Why is my chart plotter pointing wrong?

Have you checked the setting for 'course up / heading up / north up'? Also you may have to re-swing the fluxgate compass as a result of the rewire. These are easy and quick to do, before you begin spending money.
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Old 11-08-2018, 12:13   #3
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Re: Why is my chart plotter pointing wrong?

Quote:
Originally Posted by Jeanneau 45.2 View Post
Have you checked the setting for 'course up / heading up / north up'? Also you may have to re-swing the fluxgate compass as a result of the rewire. These are easy and quick to do, before you begin spending money.
Thanks, Jeanneau! I'm not on the vessel today (it's a Jeanneau SO409). I'll check the settings, but I always keep NORTH UP, since I absolutely hate the HEADING UP (whether it's my car or my vessel).

How do I re-swing the fluxgate compass? Options? Software? Hardware?
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Old 11-08-2018, 12:25   #4
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Re: Why is my chart plotter pointing wrong?

Do you have the manual to your autopilot? In the chapter "Initial Sea Trials" see the section "Automatic Compass Heading Alignment and Deviation Correction". The term "swinging the compass" comes from the calibration step where you slowly (steady 360 degree turn over at least 3 minutes) make a circle which 'swings' your steering compass 360 degrees. After you read the manual and follow the directions, PM me if you have further questions.
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Old 11-08-2018, 13:15   #5
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Re: Why is my chart plotter pointing wrong?

"Heading" comes from a compass. Likly the auto pilot. So the pilot is probably off by the same amount. Compare the heading data on screen to heading on pilot screen to a mag compass.

The 2nd pic shows cog. (From gps). Which is likly correct at speed. And compass heading way off.

The loss of pos Is probably a failing 120 or 125 gps antenna. They are old and all are failing.
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Old 12-08-2018, 09:18   #6
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Re: Why is my chart plotter pointing wrong?

is that a Raymarine CP?
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Old 12-08-2018, 09:27   #7
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Re: Why is my chart plotter pointing wrong?

I noticed a similar problem. My old Raytheon (Raymarine) chart plotter shows a ~10 degree to starport difference from Course steered to COG. Which would be normal when there is a cross current or wind, etc. But it happens all the time, under sail alone or engine running.
I tried different settings with Autohelm and on chart plotter but to no avail. Any ideas to rectify this are very much appreciated.

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Old 12-08-2018, 09:34   #8
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Re: Why is my chart plotter pointing wrong?

Defined 'Spliced In' a NMEA cable. Added a 'T' connector and drop cable? To what device?

If the new device has a GPS (Chart plotter or external GPS)it may be over-riding the compass. Heading reliability by GPS is non-existent at slow/no speed. If this may be a possibility, check your display source settings to see what priority GPS is over the compass.
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Old 12-08-2018, 10:05   #9
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Re: Why is my chart plotter pointing wrong?

Is your HDG data from a small Raymarine black puck compass perhaps?


I have seen this a lot and a lot AND A BLOODY lot coming from faulty Ray heading (compass) unit that were common on their old APs.


b.
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Old 12-08-2018, 11:38   #10
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Re: Why is my chart plotter pointing wrong?

As a suggestion to your last question: When I kept my boat in Connecticut I used Custom Navigation Systems in Westbrook to install my ST60+ wind and speed/depth instruments. They were also were very helpful with any issues I had with my Autohelm 4000.
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Old 12-08-2018, 12:09   #11
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Re: Why is my chart plotter pointing wrong?

Quote:
Originally Posted by Jeanneau 45.2 View Post
Have you checked the setting for 'course up / heading up / north up'? Also you may have to re-swing the fluxgate compass as a result of the rewire. These are easy and quick to do, before you begin spending money.
I believe he is saying, when all else fails read the manual.
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Old 12-08-2018, 12:17   #12
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Re: Why is my chart plotter pointing wrong?

Quote:
Originally Posted by Jeanneau 45.2 View Post
Have you checked the setting for 'course up / heading up / north up'? Also you may have to re-swing the fluxgate compass as a result of the rewire. These are easy and quick to do, before you begin spending money.
BINGO! Flux gate on Roxy will absolutely show our crab angle. In the Gulf Stream it was about 45 degrees. This is a good first bet since the NMEA backbone was touched and who knows what else.
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Old 12-08-2018, 15:50   #13
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Re: Why is my chart plotter pointing wrong?

It sounds as though you need to "Swing" your GPS and set your flux-gate compass to its proper heading again.

Many harbours have a buoy of known exact latitude and longitude for this purpose, and to which one can moor one's vessel; while "Swinging" it to the four points of the compass (you get your real position from the location of the buoy. Your first job is to set this position as the location of the vessel on your GPS by setting the position via the chart datum adjustments. Mine was out half a kilometre after someone changed it accidentally--it almost saw us run aground in the dark.

Having done that--put a stern anchor out using your dinghy and align your vessel fore and aft on a compass bearing from the chart. Use the magnetic setting if it has one--corrected for annual variation Holding the vessel it in this position allows you to see if the flux gate compass or the sensor has been moved. If someone has connected anything to this electric compass cable--disconnect it and connect it elsewhere. If any new cable has been laid in proximity to your flux gate compass or its cables--that is probably part or all of your problem. Once a current is flowing, it will put out a magnetic field which will affect your electronic compass.

Alter whatever it is that is not correct, alter it so that you think it should be OK.

Test it by sailing a direct course with your standard compass (not GPS) and check the GPS course line made good on the GPS electronic chart. With the vessel's magnetic heading--allowing for the magnetic variation and any deviation, it should be the same, if you did it all correctly..
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Old 12-08-2018, 16:46   #14
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Re: Why is my chart plotter pointing wrong?

Thanks guys. I'll be on the vessel on Tuesday and will post any updates. Thanks again for taking the time to give your 2 cents... it is much appreciated.
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Old 12-08-2018, 17:06   #15
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Re: Why is my chart plotter pointing wrong?

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Originally Posted by ZULU40 View Post
is that a Raymarine CP?
Yes, it's a Raymarine C120w chart plotter.
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