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    Re: Plotting practice question
    From: Rick Emerson
    Date: 1999 May 16, 21:04 EDT

    anthonys@XXX.XXX writes:
     > I think we're both on the same wavelength. It is clear that a new track
     > begins with a confident true fix.
    Er, practically speaking, the adjectives "confident true" are
    sometimes loosely applied (on a day when nothing seems to work and all
    the numbers thumb their digital noses at you [g]) but, per Bowditch,
     > What puzzles me is what you describe as "logged travel". Are you saying
     > the ship's mechanical log, which might or might not be accurate, is
     > significant?
    I'm not sure what question you're asking here.  Let me take a few
    guesses, though.
    1) When restarting the track from a [new] fix, the log reading remains
    undisturbed but is, of course, noted for future DR work.
    2) While a log might be prone to error, it's wise to at least
    determine the approximate order of magnitude (e.g., .1 nm in 10 nm, or
    something like that) if not the actual error.  If you don't have at
    least a predictable log, there's little hope of accomplishing
    meaningful navigation except by direct fixes using landmarks (remember
    that celestial nav uses, in part, DR info).
    3) The distance from the last DR (prior to the fix) to the fix is not
    included in the ship's distance covered because, quite simply, the
    ship didn't travel that leg.  Very loosely, the true track was
    something extended back from the new fix.
     > > Er, not quite, although you do have the basic points (e.g., DR error
     > > is cumulative) down.  I went back to Bowditch and in sections 703 and
     > > 704 (pp 114-115) of the '95 edition it clearly says the track is
     > > restarted with the fix.  It also says, and this is the answer to the
     > > question I raised, nothing about counting the distance between the
     > > last DR point and the fix.  As you suggest, information about the
     > > overall errors can be inferred from the direction and magnitude of the
     > > change, but it's not logged travel.
    S/V One With The Wind, Baba 35

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