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    Re: Automatic deviation calculation by electronic compasses
    From: George Huxtable
    Date: 2009 Dec 4, 17:07 -0000

    We have been discussing the use of fluxgate compasses, with automatic
    correction for deviation, in US Navy vessels.
    
    Joe Schultz wrote, in [10806]
    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.  Then, if needed, punch in an offset (this for
    the high-end, i.e. expensive equipment).
    
    So I asked-[10807]
    ...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.
    
    Joe replied-[10901
    George, the sweet spot is relative to the capability of the computer to
    create a deviation equation/table which, although you won't see it, may be
    as curvy as your favorite Greek goddess.
    
    ===================
    
    Well, yes, that's what I was asking about, but Joe hasn't added to our
    knowledge yet. Let me rephrase my question. Can a suitable place for a
    fluxgate compass always be found below decks on a steel warship, in which an
    automatic correction algorithm alone will provide sufficient heading
    accuracy for navigation, with no need for correction magnets or balls? I'm
    trying to pin Joe down to a precise answer, rather than a flippant one.
    
    Were such instruments ever actually adopted as the principal heading
    reference?
    
    Joe has shifted the discussion toward self-steering, but that's a different
    matter, as Lu has pointed out, not requiring any great precision.
    
    I can imagine that perhaps much of the inbuilt permanent magnetism of such a
    warship might well be removed at construction-time, by a de-gaussing
    procedure, as was done to ships as an emergency anti-mine measure in
    World-War 2. If that had been done, it might have improved the magnetic
    environment that a fluxgate compass faces. But the temporary magnetism
    induced by the Earth's field would be more intractable. Joe has used the
    phrase "very, very, special steel" several times. Vessels can be built from
    non-magnetic stainless steel. Indeed several yachts have been built that
    way, very expensively, but I don't know of any warships. If Joe's "very,
    very special steel" happens to be a stainless or other high-nickel alloy,
    effectively low-magnetic, I hope he will make that clear.
    
    Was this equipment used on vessels intended to operate at differing magnetic
    latitudes? If so, did operating instructions call for a 360-degree turn to
    be made, for recalibration, as the magnetic latitude changed?
    
    George.
    
    contact George Huxtable, at  george{at}hux.me.uk
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    
    --
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