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    Re: Automatic deviation calculation by electronic compasses
    From: George Huxtable
    Date: 2009 Dec 10, 00:23 -0000

    Thanks to Joe Schultz for his peacemaking response, which is accepted.
    
    He gives a reason for being unable to answer my specific question, which is
    fair enough. The question was-
    
     "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?"
    
    And my question applies to any other steel vessel, not necessarily a
    warship. Without any such specific assurance, one way or another, I have to
    say that I remain unconvinced that it can. Good enough for an autopilot,
    maybe. For a steering compass, I would like to see evidence. The fact that
    in the end, such fluxgate installations didn't get adopted as steering
    compasses, tells us something.
    
    As for his phrase about a "sweet spot", for placing such a compass, I, too,
    took a look at Wikipedia, but I could not relate that definition to the
    positioning of a fluxgate compass. I don't accept that below decks, on a
    steel vessel, there's some point at which magnetic perturbations somehow
    cancel out, or become specially small. Of course, some locations may be
    somewhat more affected than others, but it seemed to me that "sweet spot"
    was trying to imply more than that. Such are the difficulies in mutual
    undestanding, when woolly phrases are used.
    
    I followed Joe's suggestion to look at the James Husick articles, but didn't
    find anything helpful to my enquiry there.
    
    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.
    ----- Original Message -----
    From: 
    To: 
    Sent: Wednesday, December 09, 2009 1:03 PM
    Subject: [NavList 11034] Automatic deviation calculation by electronic
    compasses
    
    
    George, a gentle "heads up": I don't live in my computer.  It may be days or
    weeks before you see a response from me.
    
    I get it, regarding language.  I pick up a wrench and hand over a spanner.
    Sometimes I forget and hand over a wrench.  I'll try to improve my
    performance in language.
    
    No promises regarding how my writing "sounds."  My background isn't in
    authoring romance novels.
    
    I'll try to answer your questions and comments (post 10912) in order.
    
    1. "Can a suitable place for a fluxgate compass always be found BELOW DECKS
    [emphasis mine] on a steel WARSHIP [emphasis mine], in which an automatic
    correction algorithm alone will provide sufficient heading accuracy for
    navigation, with no need for correction magnets or balls?"
    
    I have limits, and I apologize if it appears that I've strung you along.  In
    simple terms, the "stay out of jail" card reads like this: I can talk about
    unclassified-unlimited distribution items.  The legal precedent has also
    been set so that I can talk about items that have been "leaked" into the
    press or published elsewhere, and that leads to the ethical dilemmas that
    "me and my kind" get to deal with.  That question is out of bounds, in my
    opinion.  Sorry.
    
    However, I have already stated that they were installed on all-steel ships
    and they worked.  The sensor assembly makes no real distinction between a
    steel warship and a steel commercial fishing boat or steel yacht.  Looking
    for yourself will answer the question, as I have already recommended.
    
    2. "Were such instruments ever actually adopted as the principal heading
    reference?"
    
    Not in "major" warships i.e. frigate and above.  Weapon systems reach out a
    long ways (even then).  And that's why they went away.  Today's backups are
    true.
    
    3. "Joe has shifted the discussion toward self-steering, but that's a
    different matter, as Lu has pointed out, not requiring any great precision."
    
    Nope, I'm encouraging you to look for yourself.  I thought "who in the
    civilian marine world uses this stuff?"  Autopilot users, and folks with
    integrated systems.  Standardized NMEA/ISO output signal leads to integrated
    systems.  You'll see that if you look.
    
    4. "De-gaussing."  I won't copy-and-paste your entire comment (this post is
    long enough).
    
    Magnetic influence mines are still in use.  Relating to the fluxgates, two
    deviation equation/tables were created: degaussing on and degaussing off.
    You can (and do) change the ship's magnetic signature "on the fly."  It's a
    good way to stay alive.
    
    5. "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."
    
    I inadvertently made a Navy school instructor temporarily famous.  Had a
    fellow student who was fairly intelligent but had absolutely no common
    sense.  Eventually the instructor's trip wire broke and he made a comment,
    and immediately apologized even though he was a Commander and the student
    was an Ensign.  That night I made a sign and hung it on my school desk, and
    I've hung that sign wherever I've worked.  What did it say? "Xxxxx's Idiom:
    some things are intuitive; and for that I apologize."  Xxxxx was the
    Commander's last name.  Reread the paragraphs immediately above and below
    the hazegray.org link I provided, and the link (where I told you to look),
    then engage thy brain.  If you still don't get it then I can't help you.
    Speak up and perhaps another reader will tell you what the very, very
    special steel is.  And for that I apologize.
    
    6. "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?"
    
    Yes to the first and no (with a caveat) to the second.  Made me think of two
    very real issues that I can't remember dealing with: 1) the Flinder's bar or
    unbalanced card effect, as in a "traditional" compass and 2) increased dip
    at high latitudes which will make the heading more uncertain.
    
    Mr. Husick, at the following link, can explain it better than me.  On the
    left side look for the Electronic Compasses and, ummm..., Autopilots
    articles.  Pay attention when he gets into the "old technology" fluxgate
    stuff.
    
    http://www.boatus.com/husick/default.asp?WT.mc_id=400098
    
    I do remember the "new instructions" called for a recalibration when
    necessary or when in doubt, deleting the "annual" requirement after they
    understood the stability of these systems.  Some ships went a couple years
    between recalibrations.  Believe it or not, the "old instructions" also
    called for a recalibration when entering restricted waters if the fluxgate
    was the "active" device (failure of primary).  Bureaucrats and theorists
    operate in their own world.  Their restricted waters had no traffic and had
    lots of room to turn a 450ft ship.  Recalibrating BEFORE entering restricted
    waters didn't count in their world.
    
    Now to the thread-specific questions and comments in your post 10936:
    
    1. "Sweet spot."  Hopefully this is clear to you by now, both in term
    definition and in sensor assembly location.  What do I want you to do?
    
    2. "Armchair term."  I'm not a microbiologist or a brain surgeon, and I
    won't pretend to be one.  If you've done fleet time then I apologize for
    sounding derogatory, which wasn't intended.
    
    
    George, I've said all I can say.  You really should go look for yourself.
    Bumblebees can fly.  Let us know what you learn.
    
    Joe
    
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