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Subject: Re: going overboard on decimals
From: Dan Hogan (dhhogan@XXX.XXX)
Date: Sat Jul 24 1999 - 18:37:44 EDT
RIGHT!
When I'm cruising, I round everything off to whole minutes after
getting the Almanac data and start the sight reduction. My DR is done
to the nearest whole minute. This is small boat navigation. As Hewitt
Shlereth says in Commonsense Coastal Navigation, Norton, 1982,
ISBN 0-393-03224-8. We are navigating minnows,not whales.
Silicon Sea is calculated with a computer program. I give all the data
as provided by the program. But if you are within your circle of error
you are THERE.
>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.
>
Dan Hogan WA6PBY
dhhogan@XXX.XXX
Navigation-L: http://nav.cnchost.com
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