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Subject: Re: going overboard on decimals
From: Tony (anthonys@XXX.XXX)
Date: Sat Jul 24 1999 - 16:42:48 EDT
Paul:
You bring up many good points but the fact remains that once one achieves
a reliable fix, even if done with numerous "smoothed" observations, that
is where you are (were?) at the fix time. For sure, the decimals can be
ignored but naut miles can be significant at certain times when approaching
landfall or shallow atolls. Everything depends on the confidence of the
observations. The estimated DR at the time of sights is irrelevant.
Tony in San Francisco
Paul Hirose wrote:
>
> I hope everyone realizes that after Silicon Sea runs 3 days without a
> fix, including 2 days of severe storm, the tenths of minutes from a
> digitally calculated DR are pure noise. Yes, you can copy the digits
> off the screen, but they are garbage because the inputs to the problem
> are not known with enough accuracy.
>
> Let's assume a day's run is 240 miles, more or less. If average speed
> is off by 1%, that's 2.4 miles per day. If course made good is off by
> 1 degree, that's 4.2 miles per day. Imagine how much worse this gets
> when you're being beaten up by a storm.
>
> I reported my results to only 1', and even that was overkill.
>
> Also, there's no reason to worry about seconds of time when dead
> reckoning on the high seas. In this case, it's not that you can't
> measure time that accurately. The problem is that uncertainties in
> the other parts of the DR equation - time and distance - are great
> enough to swamp any attempt to figure to the second.
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