Cockpit instruments, Don't they screw up your compass? - SailNet Community
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post #1 of 13 Old 01-28-2012 Thread Starter
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Cockpit instruments, Don't they screw up your compass?

I am planning on moving my instruments around so that one can actually see them from the helm. (novel idea I know) Currently they're all conveniently located below decks. Having the radar below, causes me to do a pretty convincing prairie-dog impression in the fog.

I notice that lots of boats with more gadgets than mine tend to cluster them right at the helm. See picture below.


How does that not mess up your compass? This issue is especially close to my heart because when I took posession of my first boat, many a navigation argument was had with me and my mate until one of us noticed that "north" always seemed to be to starboard. The external VHF speaker (with huge magnet) was located on a bulkdead right behind, and to starboard of, the main compass.

I'd like to mount mine close by, but I don't want to mess up the all important compass.

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post #2 of 13 Old 01-28-2012
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Our chartplotter and instruments are on bent helm gaurd above the compass and also downstaors at nav station. Has never bothered the compass reading




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post #3 of 13 Old 01-28-2012
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On one boat I sail there are two helm stations with a compass at each. There is a chartplotter on the port side. The compasses do not correspond. Since it is not my boat I would not pull the chartplotter to see if there is a difference.

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post #4 of 13 Old 01-28-2012
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The installation manual warns not to install the autopilot heads or plotters within a certain distance of the ships compass.. which quite obviously most installations ignore. I expect that there is an effect, though how significant I'm not sure.

Not to defend the notion, but I suspect far less reliance is being placed on magnetic compasses in this day of plotters, gps', flux gates and whatnot.

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post #5 of 13 Old 01-28-2012
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Recalibrate the compass after installation of ALL electronics, but then, still back yourselve up with a handheld ( away from electronics ) and a paper chart double check.
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post #6 of 13 Old 01-28-2012
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Lightbulb

Glad that someone pointed out that compass interference is covered in the install manuals. Any plotters with the infamous magnetic chip door closer have to be kept 17 to 37 inches away.
Since it's your life and family's lives on the line here, don't just take the word of strangers on the internet! You can D/L the manuals in PDF form for almost any modern instrument/device.

Also, if anyone tells you that they never "see" any interference with their steering compass from a close-installed electronic instrument, ask them exactly when they last had their compass swung and how current their deviation table is.



Having said all that, many instruments without obvious permanent magnets seem to coexist within a foot of compasses. This would include your DS, Speed, and Wind readouts.

L
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post #7 of 13 Old 01-28-2012
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Quote:
Originally Posted by olson34 View Post

Having said all that, many instruments without obvious permanent magnets seem to coexist within a foot of compasses. This would include your DS, Speed, and Wind readouts.

L
And watch out for magnetized clip-on sunglasses when using a handbearing compass.
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post #8 of 13 Old 01-29-2012 Thread Starter
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Quote:
Originally Posted by poopdeckpappy View Post
Recalibrate the compass after installation of ALL electronics, but then, still back yourselve up with a handheld ( away from electronics ) and a paper chart double check.
I was thinking I could do that. Just install all the whiz-gadgets that I could afford, then have the compass swung. But wouldn't they interfere differently when they are on as opposed to off?

As for reliance shifting away from the compass, that ain't happening on my boat. I still have a leadline handy at all times and use it often. I distrust mechanilectronics and while I often enjoy using them, I like having as manual and foolproof of a backup system as is practical. So, to me the compass it somewhat sacred.

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post #9 of 13 Old 01-29-2012
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I recently installed a Lowrance HDS-5M near to the compass. I tried moving it around to see if I could cause any deviation in the compass reading. To either side I could, but slight - about 2 or 3 degrees. But as long as the chartplotter was above the height of the compass, it could be quite close and the deviation was undetectable. Lowrance have a spec for proximity to the compass. 8".

Note it's also recommended that any wires going to devices near to the compass are twisted together to avoid stray magnetic fields from those.

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post #10 of 13 Old 01-29-2012
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Quote:
Originally Posted by olson34 View Post
Glad that someone pointed out that compass interference is covered in the install manuals. Any plotters with the infamous magnetic chip door closer have to be kept 17 to 37 inches away.
Since it's your life and family's lives on the line here, don't just take the word of strangers on the internet! You can D/L the manuals in PDF form for almost any modern instrument/device.

Also, if anyone tells you that they never "see" any interference with their steering compass from a close-installed electronic instrument, ask them exactly when they last had their compass swung and how current their deviation table is.



Having said all that, many instruments without obvious permanent magnets seem to coexist within a foot of compasses. This would include your DS, Speed, and Wind readouts.

L
My Lowrance HDS_5M has the magnetic chip door latch and safe distance is 8".

Bristol 31.1, San Francisco Bay
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