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    Re: Why Not To Teach Running Fixes
    From: Byron Franklin
    Date: 2009 Dec 15, 10:37 -0800

    Why teach the running fix? For Tradition and for rounding out the
    sailor.
    The interesting way to teach Navigation is to teach what and how
    things were done in the past and in the future.  The example given
    showing above Wierd
    The running fix and the �bow and beam� were important technique at one
    time; they are based on the DR. and the Navigator judgment. (No black
    box) They both are based on the ships course and speed. Both should be
    evaluated and should use the third  or more LOPS.  The running fix
    (right or wrong) has always in all courses and text been labeled as a
    fix, you can�t change that that because of continuity.  If you denied
    the running fix as poor information bases, then you must denied the
    DR. and countless other techniques used in the past and still being
    used. You must know many techniques with this same base. Two
    techniques that submarine use are bottom contour and tracking targets.
    The sub can�t use active sonar and must track other ships by passive
    in coming bearings only. The sonar man can give good information as to
    the targets speed, a marked speed stick is used to conform to the
    bearings, giving target course speed and distance. I have trust the
    DR. correctly over the black box many times.  This is the Practical
    Navigator.
    
    
    On Dec 15, 1:18�pm, John Karl  wrote:
    > Lu & Gary,
    >
    > Yes, there are cases where the LOP accuracy is less than the accuracy �
    > of the estimated track. �But I said at the outset that I'm considering �
    > the opposite case, where the LOP accuracy is significantly greater �
    > than the track accuracy. �This occurs quite frequently with running �
    > fixes, such has in a one, or more, day's run with no new LOPs.
    >
    > In the first attached figure (labeled Uncertainties) regions of �
    > uncertainty are show in blue, the LOPs are drawn as lines, indicating �
    > that the uncertainty perpendicular to them is negligible. �When LOP1 �
    > was acquired, the uncertainty surrounding EP1 was effectively �
    > collapsed to a line by LOP1. �After a run of some length, the dark �
    > blue line at EP1 expands equally in all directions as shown. �A MAJOR �
    > OBSERVATION is that the distance from DR1 to EP2 is always less than �
    > the distance from DR1 to RFIX. �(These distances are equal if the two �
    > LOPs are perpendicular.)
    >
    > That is, unless more is known about the shape of the uncertainty �
    > region surrounding DR1, EP2 is always a better estimate than is RFIX. �
    > Dropping a perpendicular from DR1 to LOP2 is a better estimate than �
    > the traditional running fix.
    >
    > The second figure (labeled Weird Uncertainties) shows an example where �
    > by some weird circumstance the DR uncertainty just happens to have �
    > grown, known to the navigator, more along the advanced LOP1 than �
    > perpendicular to it. �It's difficult to image a practical situation �
    > where this would happen.
    >
    > All this is simply said by noting that the Estimated Position concept �
    > fully honors the new LOP2 while retaining the information in the DR �
    > that is not contradicted by LOP2.
    >
    > And Lu, the two tracks in my previous figure need not be the same �
    > length. �They are just an example of two tracks that have the same �
    > perpendicular distance between LOP1 and its advance (speeds and even �
    > times can be unrelated).
    >
    > JK
    >
    >
    >
    > �Uncertainties.jpg
    > 60KViewDownload
    >
    > �Wierd Uncertainties.jpg
    > 65KViewDownload
    >
    >
    
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