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    Re: Automatic deviation calculation by electronic compasses
    From: George Huxtable
    Date: 2009 Nov 25, 00:45 -0000

    Joe Schultz described fluxgate compasses as "First tried at the fleet level
    in the first gas-turbined frigates (US Navy) at least 25 years ago."
    To which I replied-
    "I wonder: were those "first gas-turbined frigates" that Joe refers to,
    of steel? If so, I'm interested in what, if anything, was in place as a
    first-order correction for deviation, if these were, as Joe's words
    "self-correcting" compasses. Did they have the familiar correction magnets,
    and the hollow soft-iron spheres placed to port and starboard of the compass
    housing? I would be surprised if any electronic correction algorithm, such
    as we have been discussing, was capable of tackling the enormous deviations
    that a steel vessel gives rise to, without some such first-order
    And Joe has responded-"Yes, George, US Navy ships are made of steel.  Very,
    very special steel..."
    Well, it wasn't such a dumb question as that. Some Royal Navy vessels have
    been designed with aluminium-alloy superstructure above a steel hull, (with
    fatal consequences in the Falklands war). Which would reduce, though not
    eliminate, the need for correction for induced magnetism.
    And he added-
    "The advantage of these "electronic" compasses is that you can put the
    sensor assembly anywhere you want - no need for "Navigator's Balls."  Find
    the sweet spot and put it there."
    Tell us how well that works, please, Joe. I can see that a remote-reading
    compass can be put at the top of a mast (with which warships bristle)  and
    that could perhaps move it far enough away from hull-influence, so that
    internal-correction might suffice. But can Joe's "sweet spot" be located
    anywhere below (where accelerations will be less) in a steel hull and still
    avoid the need for the iron balls? Joe seems to be speaking with some
    authority on this topic, and I hope we can discover more.
    contact George Huxtable, at  george@hux.me.uk
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    NavList message boards: www.fer3.com/arc
    Or post by email to: NavList@fer3.com
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