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Subject: Re: [Nml] Re: GPS backup/emergency navigation
From: Rick Emerson (rick@XXX.XXX)
Date: Thu Nov 26 1998 - 23:16:18 EST
Denis Gutar writes:
>Rick Emerson writes:
> >A friend wrote the following comments in response to a discussion
> >about the need for sight reductions with the Nautical Almanac and
> >sight reduction tables of some sort (e.g., HO 249) versus doing the
> >reductions by solving the navigation triangle "by hand".
> >
> >[...]
> > > No you don't, i.e. need an almanac or HO 249. Well, you need an
> almanac,
> > > but the perenial one in Bowditch that's about 3 or 4 pages long will
> > > suffice for the sun and stars. It's based on the fact that the almanac
> > > nearly repeats every 4 yrs. and a fudge factor is added. A few basic
> trig
> > > formulas and you don't need 249
[...]
>
> Would anyone please scan these 3 or 4 pages from Bowditch for us the
> arnchair navigators?
>
In my 1966 edition, this section is called Appendix X (it follows
Appendix W), "Long Term Almanac" (pp.1160-1164) and provides
corrections to be applied to any almanac to adjust it for the same
date plus 4 years (e.g., advancing a 1995 Nautical Almanac to 1999).
This works because it's the number of years needed to complete one
leap-year cycle and bring the almanac approximately back into sync.
The section contains five pages including three of fine print tables.
Scanning them would involve either high resolution images (and many
megs per page) or highly accurate OCR gear.
Frankly, nobody should be without a Bowditch if they're at all
interested in navigation. Look in the used book web pages (I like
www.bibliocity.com) for a used copy from the 60's through 80's. the
furth back you go, the furhter off the sections on electronics are but
otherwise, there are some tables in the earlier editions which
vanished in later editions.
Rick
S/V One With The Wind, Baba 35
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