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    Re: The Nonsensical Running Fix
    From: Gary LaPook
    Date: 2010 Oct 25, 01:03 -0700
    Karl's article is interesting but it appears to ignore uncertainty in the LOP and assigns all the uncertainty to the DR. The Air Force has a standard method for dealing with the situation in Karl's article which deals with the relative uncertainties in both the LOP and the DR. I have attached several pages from the current Air Force navigation manual, AFPAM 11-216 (you can download the entire manual here: http://www.e-publishing.af.mil/shared/media/epubs/AFPAM11-216.pdf  but the same information had been published in the predecessor manual, AFM 51-40) that shows how to account for the relative uncertainties but would have to modified for marine practice.


    On 10/24/2010 11:32 AM, Dr. Wolfgang Köberer wrote:

    I’ve read John Karl’s article with interest, but I have to admit that I do not completely follow his reasoning:


    As I understand he thinks that dropping a perpendicular from the position DR2 to the LOP2 gives an EP2 which should be preferable to a running fix from advancing LOP1 along the DR track. What I don’t understand is why the best estimate should be where a perpendicular from DR2 meets LOP2. Of course an error in measuring the height of the heavenly object moves LOP2 only along the perpendicular, but that is no sufficient reason to assume that the best estimate of the position is on the perpendicular passing through DR2.


    Or should we prefer that EP because it is the closest point  on LOP2 – being located on a perpendicular to it. Why that?


    His Figure 3 is rather suggestive, but it only shows that the running fix may be way off from the EP2; it does not show, though, where the error lies: is LOP1 wrong, or LOP2 , or is there a strong current/faulty compass etc.? Or should we just trust DR more than LOPs?


    Have I got something wrong there? I have to admit that my practical experience as a navigator stems from rather restricted waters (Baltic, Zuiderzee, Greek archipelago, Turkey, Western Mediterranean) with little current and no need for astro LOPs. And crossing the Atlantic we relied on GPS.




    Von: navlist-bounce@fer3.com [mailto:navlist-bounce@fer3.com] Im Auftrag von Gary LaPook
    Gesendet: Samstag, 16. Oktober 2010 02:29
    An: NavList@fer3.com
    Betreff: [NavList] The Nonsensical Running Fix


    John Karl's article has been published in this month's Ocean Navigator, attached.



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