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06-02-2021, 10:20 AM
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#1
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Guru
City: Dewatto
Vessel Name: CHiTON
Vessel Model: Tung Hwa Clipper 30
Join Date: Jan 2020
Posts: 1,096
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Found a magnet near my compass
I've had some concerns with how close my compass is to my Garmin EchoMap MFD. It was installed by a local boat yard and I thought maybe they had determined that the screen doesn't have much effect on a nearby compass.
Yesterday, I was setting up the Garmin WiFi to work on a laptop to be used on the upper helm. I was opening a little door on the MFD that holds a mini SD card inside. I noticed that the door snapped shut like it was held closed by a tiny magnet. The little door is closer than a foot from my compass. Sure enough, opening and closing the door made a 4 degree difference in the compass reading. Today I'll watch the compass as I turn on the Garmin and see if that has an effect. Maybe remove the magnet from the door? Seems like an odd closure mechanism on an MFD when there's a 99% chance of a nearby compass.
__________________
Marco Flamingo
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06-02-2021, 10:22 AM
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#2
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Enigma
City: Slicker?
Join Date: Oct 2007
Posts: 16,566
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Greetings,
Mr. MF. Perhaps the yard was unaware of the magnet in the device OR didn't care. Like, who uses a compass anymore (I do).
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RTF
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06-02-2021, 10:45 AM
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#3
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Senior Member
City: Oceanside, CA
Vessel Name: Tera Grace
Vessel Model: Californian 42 LRC
Join Date: Oct 2012
Posts: 197
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You can check the documentation for the Garmin and it will list the Minimum Safe Compass Distance. A quick look on line indicates somewhere between 21-25 inches depending on model.
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06-02-2021, 12:46 PM
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#4
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Guru
City: Southport, FL near Panama City
Vessel Name: FROLIC
Vessel Model: Mainship 30 Pilot II since 2015. GB-42 1986-2015. Former Unlimited Tonnage Master
Join Date: Oct 2007
Posts: 4,984
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It is probably a spiral wound spring in the door hinge of the Garmin that is slightly magnetized.
__________________
Rich Gano
FROLIC (2005 MainShip 30 Pilot II)
Panama City area
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06-02-2021, 07:39 PM
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#5
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Guru
City: US PNW
Join Date: Nov 2018
Posts: 943
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Quote:
Originally Posted by TG
You can check the documentation for the Garmin and it will list the Minimum Safe Compass Distance. A quick look on line indicates somewhere between 21-25 inches depending on model.
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Just as a note: My Raymarine Axiom manual does the same, but there are different distances specified for the various sides of the chartplotter. I never looked up my previous (Garmin) as I had not installed it.
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06-02-2021, 08:01 PM
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#6
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Guru
City: West Coast
Join Date: Apr 2014
Posts: 1,790
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Quote:
Originally Posted by Marco Flamingo
The little door is closer than a foot from my compass. Sure enough, opening and closing the door made a 4 degree difference in the compass reading. Today I'll watch the compass as I turn on the Garmin and see if that has an effect.
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You probably know this, but in case you don't, the affect that magnet will have on your compass will vary depending upon the direction of the magnet from your compass, relative to magnetic north. If in line with magnetic north -- no affect at all. If, say, 10 degrees out of line, perhaps only 4 degrees. If 90 degrees out of line with magnetic north, perhaps much more than 4 degrees.
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06-02-2021, 08:09 PM
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#7
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Moderator Emeritus
City: Au Gres, MI
Vessel Name: Black Dog
Vessel Model: Formula 41PC
Join Date: Jul 2015
Posts: 21,191
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Yes, deviation does change relative to headings. Sometimes wildly.
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Boat Nut:
If you are one there is no explanation necessary.
If you aren’t one, there is no explanation possible.
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06-02-2021, 10:12 PM
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#8
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Guru
City: Jacksonville Beach, FL
Join Date: May 2015
Posts: 1,252
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It's unnecessary for an object to be magnetized to affect a magnetic compass. Anything ferrous in close enough proximity will move your compass card.
__________________
"Less judgment than wit is more sail than ballast. Yet it must be confessed that wit give an edge to sense, and recommends it extremely." ~ William Penn
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