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    Re: Re Compass Adjustment - A Cautionary tale
    From: George Huxtable
    Date: 2005 Jan 31, 21:09 +0000

    Relating to this thread, I have just received privately an email from
    "Giuseppe Menga" .
    which is copied below.
    He tells me that he has tried to send it as a posting to Nav-l, but for
    some reason that he does not understand, submissions via polito.it are
    being rejected.
    As it seemed a useful and relevant comment, I am copying it to the list for
    > I followed with interest this thread.
    > Then come to my mind a question: How do behave from this aspect modern
    > electronic compasses, as the fluxgate, embedded in the auotpilots (e.g
    > Raymarine) of current sailing boats?
    > Also for these compasses has one to pay attention to the change of zone?
    >  Giuseppe Menga
    Giuseppe's question brings to mind my old Autohelm, which is a Nautech 1000
    (predecessor to the Raymarine range). I've inspected the innards, and the
    fluxgate unit is pivoted in a gimbal mounting. Not a very good gimbal
    mounting, in my opinion, because several  electrical leads have to be
    brought out from the fluxgate to the rest of the circuitry, by means of a
    flexible printed strip, and any stiffness in that loop of strip affects the
    ability of the gimbals to swing with complete freedom.
    My own opinion is that a fluxgate requires much better gimballing than does
    an ordinary magnetic compass, because that compass has its own gimballing
    and then on top of that the point-pivot gives the card further freedom to
    find its level; a freedom that the fluxgate lacks.
    My old self-steering does not possess any way of displaying the course set;
    it has only the ability to lock on to that course, whatever it happens to
    be. In that case, there's no stringent requirement for accurate course
    determination; all that's needed is for it to be reasonably consistent.
    A weakness I have found was that the gimballed fluxgate had a little rubber
    o-ring "tyre" around it, to cushion it at the extremes of rock-and-roll.
    That's fine, except that when it reached those extremes, the tyre tended to
    wedge itself against the housing, and the gimbal mechanism would then stick
    at maximum tilt, with disastrous effects on the steering! Removing the
    o-ring cured the problem.
    Those musings about my self-steering are not intended to address Guiseppe's
    question, which remains to be answered.
    contact George Huxtable by email at george@huxtable.u-net.com, by phone at
    01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy
    Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.

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