NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Why are NA sight reduction tables not popular?
From: Lu Abel
Date: 2012 Apr 8, 12:11 -0700
From: Lu Abel
Date: 2012 Apr 8, 12:11 -0700
What do you mean by "the NA LOC method?"
Sent from my iPhone
Sent from my iPhone
I personally like the Nautical Almanac Concise method, but I have heard it is unpopular because it requires "three page openings". I don't find the pages all that heavy . I guess what is really being said is that it is more subject to error because of the number of page openings. I don't see it myself.
The Law of Cosines is being taught in the Power Squadron Junior Navigation course, with the Nautical Almanac Concise method being added in the Navigation course
You really can't compare the Law of Cosines "calculator" method, regardless of which formulae are used, with a tabular method like the Nautical Almanac Concise method. Let's face it, if you don't have a calculator or a computer, the Nautical Almanac Concise method has the advantage over other tabular methods in that everything you need, no matter where you are located, is already included in the book you must have anyway, the Nautical Almanac. Sure, it only gives 1 nm resolution, but I think its advantages outweigh its disadvantages.
As to why the Power Squadrons does not use the NA version of the Law of Cosines formulae, that I do not know.
Stan
-----Original Message-----
From: Geoffrey Kolbe <geoffreykolbe@compuserve.com>
To: NavList <NavList@fer3.com>
Sent: Sun, Apr 8, 2012 3:44 am
Subject: [NavList] Why are NA sight reduction tables not popular?
Frank said that he didn't know anyone who liked them (or words to that effect). Given that the NA tables system is taught in Power Squadron navigation classes, I would have thought that the biggest hurdle of any system - becoming familiar with the method - would have been overcome and made this method popular. The NA sight reduction system has the advantage of being angles all the way, so you are not changing in and out of logs, and once you get the hang of it, this method seems to be as quick as any. Any thoughts on why it is not popular? Lu Abel says that the "Law of Cosines" is what is being taught to the Power Squadron these days as the principal method of sight reduction. I went and had a look at the Power Squadron website and sure enough, in the 'Nautical Tools' section, there is a handy little online sight reduction program, showing the formulae used - and presumably taught in Power Squadron classes. Now, there may be good reasons why the NA sight reduction tables are not popular, but as was pointed out some years ago by Herbert Prinz, the formulae given in the NA for sight reduction using a calculator are the best formulae available for a number of reasons and I am surprised that the Power Squadron do not teach those instead. The formulae for Hc is the same, but the Power Squadron formula for Zn blows up in polar regions, whereas the NA version does not. Geoffrey