NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Automatic deviation calculation by electronic compasses
From: George Huxtable
Date: 2009 Dec 4, 17:07 -0000
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@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 To , email NavList+@fer3.com