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----- Original Message -----
From: "George Huxtable" 
To: 
Sent: Sunday, January 30, 2005 10:48 PM
Subject: Re: Re Compass Adjustment - A Cautionary tale
(Snip)
>. Unfortunately, this
> renders the compass more susceptible to the sideways accelerations of a
> vessel in a seaway. Also, the geometry was altered so that the card could
> tilt further before it fouled anything. In that way it was possible to
make
> a compass that would work anywhere in the world, but it's a matter of
> compromise.
>
> Presumably, a compass that's designed to operate in a restricted zone of
> magnetic latitudes would be a better performer, in terms of motion
> stability, than a "global" compass.

George, I don't understand what you are saying here, and wouldn't mind a
reference or source  to help develop what you are saying. My imperfect
understanding at the moment is that the only difference between a zoned and
a global needle is the bearing that the needle/card rides on. As I
understand it, a global needle is based upon a more intricate and expensive
bearing. A bearing that allows the needle to swing freely, despite the force
of magnetic dip upon it. Properly built, it is unclear to me that a global
needle will function any different to a zoned needle.

Your comments on compass adjustment support my growing belief.....that
ship's compass adjustment is to neutralize the magnetic effect of the ship,
and that adjustment for magnetic dip is a separate issue, to be addressed by
weights , etc.. However, I would love to hear from a professional compass
adjuster on this issue.

Lee Martin

   

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