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Subject: Advancing and retiring LOP's
From: Richard B. Emerson (navsys@XXX.XXX)
Date: Thu Aug 03 2000 - 09:03:36 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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