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    Re: Why Not To Teach Running Fixes
    From: Jeremy C
    Date: 2009 Dec 14, 15:15 EST
    I will try to be concise here and answer retorts as posted.
     
    First why R. Fixes are taught.  Well they do have only limited use in pilotage waters, where there should be a plethora of known, fixed objects available for a good round of bearings.  This being said, to ensure accuracy of these fixes on the large scale harbor charts, you need simultaneous bearings.  Navy ships can do this, but small craft with one bearing compass, and merchant ships with one bearing taker; cannot shoot them all at the same time.  You shoot them as quickly as possible, and to get the best fix, you retard or advance the LOP's to a common time.  To do this you use the assumption that the ship traveled a fixed distance along its track in a certain amount of time.  This is an assumption and ignores the parallel motion.  You can excuse this because in the minute or two between these bearings, the error due to a change of speed as well as motion parallel to the track will be negligible.  This error will however become larger with time, and should be in the back of the mind of any navigator using running fixes.
     
    In Celestial navigation, unless you are operating in extraordinary circumstances, ALL star fixes are running fixes.  In order to obtain a C. Fix at a set time, you need to know the concept and methods of obtaining a running fix.  The same assumptions apply with greater errors due to increased time but we can also forgo accuracy a bit because it is not as critical in the open ocean.  If you don't teach the technique, you aren't going to be able to make much of a fix, just a bunch of lines at all different times.
     
    For "near coastal" waters, say 12-15 miles off shore, and the only time I've ever used a classic running fix at sea; I accept that I have reduced accuracy for the very reason that I am entirely unsure of how accurate my advanced LOP's are.  Again, due to the distance from land during these times, I am not too worried about a bit of error in position.  For these fixes, I usually am advancing a visual LOP of a now disappeared lighthouse and crossing it with a radar range or two.  It is the last terrestrial navigation I do before switching entirely to electronic/celestial.
     
    As far as marking on a chart, the symbols I use are triangles for electronic fixes, circles for visual or celestial fixes, circle with "r. fix" next to it for a running fix, rectangle for EP, and a half circle for DR.
     
    Jeremy
     
    In a message dated 12/13/2009 6:23:54 P.M. Eastern Standard Time, jhkarl---.net writes:
    My argument against running fixes has nothing to do with how they're 
    taught, but it does challenge why they're taught -- at all.

    It has nothing to do with how the location DR2 was estimated.  As long 
    as DR2 is found by combining relatively inaccurate data, and not by 
    forming a fix of a third LOP with LOP2, it is irrelevant what (or 
    which) estimates are included in DR2: speed, time, logged distance, 
    drift, current, averaged headings, the flight of birds, etc.  I'm 
    talking about arriving at DR2 without a bona fide fix.

    I pointed out that the concept behind the traditional running fix is 
    based on two ridiculous assumptions: the assumption that the estimated 
    DR track perpendicular to LOP1 is completely accurate while the DR 
    component parallel to LOP1 is completely without value.

    I ask again, can anyone on the List refute these these two 
    assumptions??  Can anyone justify them??

    Ah, the traditions of the sea.

    JK

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