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Subject: Re: [worldcruising] Electronic Charts systems
From: James Forsyth (sailors2@XXX.XXX)
Date: Thu Jan 25 2001 - 16:36:36 EST
Kelly,
It's been a few years since I fired up my sextant, but my recollection
is that you still need the ephemeris data from the almanac as well as the
tables in 249 or 229.
James Forsyth
S/V Moonshadow
----- Original Message -----
From: "Kelly McDaniel" <kelly.mcdaniel@XXX.XXX>
To: <worldcruising@XXX.XXX>
Sent: Thursday, January 25, 2001 2:44 PM
Subject: RE: [worldcruising] Electronic Charts systems
As an alternative to purchasing the Nautical Almanac on a yearly basis, You
may wish to add any or all of the Sight Reduction Tables for Marine
Navigation - Pub. 229 which comes in six volumes:
1 - Latitudes 0° - 15°, inclusive
2 - Latitudes 15° - 30°, inclusive
3 - Latitudes 30° - 45°, inclusive
4 - Latitudes 45° - 60°, inclusive
5 - Latitudes 60° - 75°, inclusive
6 - Latitudes 75° - 90°, inclusive
Alternatively you could use the Sight Reduction for Air Navigation - Pub.
249 which comes in three volumes:
1 - Vol. 1 (Selected Stars) 2000 Ed. (Epoch 2005.0)
2 - Latitudes 0° - 40°, Declinations 0° - 29°
3 - Latitudes 39° - 89°, Declinations 0° - 29°
Kelly _/)
-----Original Message-----
From: jan bruggeman [mailto:jan.bruggeman@XXX.XXX]
Sent: 2001 January 25 1:56 AM
To: worldcruising@XXX.XXX
Subject: Re: [worldcruising] Electronic Charts systems
Hello list,
<snip>
> Perhaps the operating systems used for the GPS satellites themselves are
> using Win 95 or Win 98? I would strongly urge you to reconsider
alternatives
> to relying solely on GPS for navigation.
</snip>
Good joke ! I personally hope they are running linux. And I'm sure this
discussion can go on and on. Let me make just some more
point for astro-navigation !
- Do you know that you only need 4 almanacs, of 4 concecutive years ? the
5th year, you just use almanac 1 over again, and so on. This will only
induce a very small error, much smaller than the errors in the almanac
itself (due to rounding of numbers). You can certainly use almanacs of
2001 - 2004 until 2050 ! of course, within 200 years or more, the error
will
become bigger. The theory behind this:
* every 4 years we add 1 day to the calender (29 february) to cope with
"the
biggest error" : that's why I say you need 4 concecutive almanacs
* after 400 years we take away 1 day out of the calender (there was no 29
february 2000 due to this rule) because rule 1 is too rough.
So using almanacs over and over again will induce an error of 1 day in 400
years. Perhaps you're better to buy new almanacs now as we've just lived
thru such a correction, they will be usable till the end of your sailing
carreer, unless your under-age while reading this ;-)
And the feeling you get when you manage to make a point on the chart after
your sextant work is reason enough to go thru the whole process of
learning
!!!
mvg,
Jan Bruggeman
mail : jan@XXX.XXX
web: http://jan.bruggeman.com
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