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Author Topic:   Mounting Compass next to vhf unit on 170 Montauk
osillator posted 03-18-2003 10:35 PM ET (US)   Profile for osillator   Send Email to osillator  
I have a new Ritchie supersport compass to mount in the factory position on my new montauk. Boat did not come with compass.

I want to mount my Shakesspeare model SE 2510 just to the right of it. I heard a rumor that the VHF radio could make the compass unhappy??

Does anyone know the answer? Please help.

jimh posted 03-18-2003 10:59 PM ET (US)     Profile for jimh  Send Email to jimh     
A compass is an extremely sensitive indicator of magnetic lines of force. The source of this magnetic energy is the magnetic pole, which is roughly in northern Canada, or thousands of miles away.

In your radio there is a very strong, by comparison, magnet that is associated with the internal radio loudspeaker. It is possible that the loudspeaker magnet is magnetically shielded to reduce any external field, but even if it were it might still affect the sensitive compass.

If you want to maintain your compass as an accurate navigation tool, I would separate the radio from it as much as possible.

Jerry Townsend posted 03-19-2003 11:44 AM ET (US)     Profile for Jerry Townsend  Send Email to Jerry Townsend     
Oscillator - Jimh is right on. Also realize that not only magnets (as in a speaker) will influence the compass - but also any metal (knife, metal in the vhf, will similarily influence the compass - as the compass has an internal magnet. In short, keep everything away from the compass as possible. ------ Jerry/Idaho
bsmotril posted 03-19-2003 11:56 AM ET (US)     Profile for bsmotril  Send Email to bsmotril     
This is definetly true, and I learned it the hard way. I have my VHF in the dash electronics box under my compass. Receiving, it gives me a 15 degree compass error. Transmitting, it jumps to 30 degrees. I am going to move it this summer when I upgrade some of my electronics.
TightPenny posted 03-19-2003 04:46 PM ET (US)     Profile for TightPenny  Send Email to TightPenny     
Keep them separated.

I mounted my radio on the aft face of the console of my 2000 Montauk to avoid that problem. Fortunately I found the interference prior to drilling the holes.

triblet posted 03-19-2003 09:40 PM ET (US)     Profile for triblet  Send Email to triblet     
Speakers have a semi-serious magnet in them
(I say semi- because I mess with some SERIOUS
magnets at work.)

You'll need to keep them separated. I had to
move my compass when my VHF screwed up the

Run an experiment on the kitchen table.
Put the VHF and compass on the table, then
slide the compass to the left. Watch the
needle. Turn everything 90 degrees, and
repeat, Repeat two more times. If there's a
problem, and I suspect there will be (ESP if
the speaker is on the compass side of the
VHF), you'll see it.

I found that at least 12" clearance between
compass and speaker is required. 18" is


jimh posted 03-19-2003 11:49 PM ET (US)     Profile for jimh  Send Email to jimh     
To demonstrate the sensitivity of the compass to external magnetic influences, I want to point out that in Northern Lake Huron and also in Lake Superior there are many areas where the local magnetic variation is much different than the average. This effect is caused by the presence of high densities of iron ore in the lake bottom.

The area between Cockburn Island and Manitoulin Island contains some shoals named "Magnetic Reefs" because the local magnetic variation is large and has contributed to many shipwrecks.

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