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    Advancing and retiring LOP's
    From: Richard B. Emerson
    Date: 2000 Aug 03, 09:03 EDT

    I recently ecountered a set of circumstances that left me confused and
    somewhat shaken about my nav skills.  Specifically, this past June on
    a trip from Cape May to Block Island, with Montauk Point in sight, I
    came up with a running fix that was about 30-35 miles off from my
    predicted DR position.  The running fix was based on the previous
    day's noon line at about 1700 (all times GMT), a round of sights at
    2000 for a second sun line, and, the following morning, at about 1200.
    The day 2 1200 sights clustered reasonably well (about a 2 to 3 mile
    spread in distance from the AP) but consistantly produced a result
    that was blatantly wrong.  I have since diagnosed the problem and I'm
    very comfortable with the corrected results.
    I want to ask a question that was posed by this incident: while
    acknowledging that there is dilution of accuracy in advancing (or
    retiring) LOP's as they age (that is, the older an LOP is, the less
    confidence a navigator should have in advancing that LOP down a DR
    track), it's been my impression that any LOP within the current
    navigation day (i.e., noon to noon) is fair game for advancing or
    retiring.  This implies that, with the understanding of loss of
    accuracy with time, LOP's as much as 23 hours 59 minutes old can still
    be used and that LOP's over 12 hours old are certainly still usable.
    Finally, for very specific reasons, I do *not* want to discuss where
    the initial error came from or how the sight reductions were done.
    The only question I'm asking is regarding the age of LOP's and their
    suitability for advancement or retirement.
    Rick
    S/V One With The Wind, Baba 35
    

       
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