[Rhodes22-list] Compass

[Jim White]

Slim:
A magnetic compass is generally tested for accuracy in installation by a 
process called "swinging". Here's a couple of links to swinging a marine 
compass:
http://education.qld.gov.au/curriculum/area/maths/compass/html/coastalnav/cnswi.html

http://www.terrax.org/geography/compass/compass.aspx

I have done this on both aircraft and boats, and it is often a big  PITA, 
but worth it for accuracy sake.

The compensating magnets are used whenever there is a source of 
interference (i.e. iron or other metal objects which would affect the 
static accuracy of the compass).

You could check the accuracy of the compass by removing it, and testing it 
on a compass rose oriented with a known accurate compass.

jw


At 04:49 PM 4/6/2005, you wrote:
>The previous owner of my boat had a removable six inch high board that sat
>across the companionway.  On it he mounted a compass AND an auxiliary
>speaker for the radio.  An ill-fated feat of engineering since the compass's
>proximity to the speaker (magnet) rendered the compass useless right from
>the get go. Needless to say, I've never used the thing and it's been stored
>in my garage all these years.  But I pulled it out the other day and removed
>the speaker.  The compass now seems to point north OK but I'm wondering if
>it's damaged or compromised by sitting next to the magnet all this time.
>It's a Ritchie B-80.  It has what I assume to be a calibration screw on the
>front, but I don't know how to calibrate or test a compass.  Any advice?
>
>Thanks,
>
>Slim
>
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Jim White
Le Menagerie
www.lemenagerie.blogspot.com