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Rick:
My question related to your own statement ....
> > overall errors can be inferred from the direction and magnitude of the
 > > change, but it's not logged travel.
                      ^^^^^^^^^^^^^^^^^
This was not clear to me inasmuch as we use "log" in several ways and for
differing purposes.
A true fix (not running fix) is the best we can come up with, not so?
Confidence level can be quite variable since "our" sights are from a
very unstable platform; compare to a ship, for instance.
Dan: re your question ...will you buy 3 to 5 miles?  ;)
Tony
Rick Emerson wrote:
>
> 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,
> yes.
>
>  > 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.
>
> Rick
> S/V One With The Wind, Baba 35

   

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