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Re: Why are NA sight reduction tables not popular?
From: Robert Eno
Date: 2012 Apr 8, 11:27 -0400
From: Robert Eno
Date: 2012 Apr 8, 11:27 -0400
Apologies if this gets sent several times. My system is having problems with responding to this list. ----------------- I'll wade in here once again. This topic was discussed a few years ago wherein I made the same comments. I'll preface my comments by stating that I have practiced astro-navigation since 1983 so I am not a neophyte. Not an expert either: just a well-practiced old codger. Now on to my comments: Back in 1990, I was summer stupid (summer student) working with a scientific research party near the Beaufort Sea. I had gone back to college relatively late in life to pursue a different career. Anyway, we were going to be in this field camp for 3 months so I took along my sextant, tables and other accouterments, knowing that I would have plenty of spare time on my hands; so why not use it to hone my skills. During this time, I tackled the tables at the back of the NA. I spent hours trying to master them and ended up hating them. Why? I found them to be too complex in that there are too many steps; too much transposing and mixing and matching of numbers. Even after I had come into a groove with these tables, I found I was still making stupid mistakes - blunders. I came to the conclusion, from a personal perspective, that these tables simply were not trustworthy enough if I found myself in a tight situation. Not that the tables weren't trustworthy, but that I could not be relied upon to employ them without the possibility of blunders creeping into the equation. The ostensible reason for having these tables is that they will be a back-up in the event of an emergency. And in an emergency, stress levels are high. The last thing a navigator needs under such conditions, is a set of sight reduction tables that, due to the design, are prone to user blunders. During times of stress, a navigator needs a sight reduction system that is simple, fast and has a minimum number of steps. In my humble opinion, the best short system, notwithstanding the "forbidden zone" is HO 211 - Ageton. With a proper sight reduction form, Ageton is fast, easy, reliable and less prone to the generation of blunders. My all around preferred method is the spherical triangle formulas with a scientific calculator. I will admit here that I have never been great at math. It is a subject that I have always had to work hard at to master and this may be part of the reason why I found the NA tables to be tedious and difficult. As I understand it, the NA tables were developed in part by the late Admiral TD Davies who was, by all accounts a brilliant mathematician and a brilliant man all around. Regrettably, not all of us -- yours truly included -- are so conferred with genius. What is elementary to the luminary may be well above the heads of the average navigator. We have a lot of intellectual heavyweights on this list for whom the finer points of mathematics is second nature. But it should also be understood that traditionally, the average navigator only concerns himself with the end result: finding his location as quickly and easily as possible. So there is my two bits' worth. From the perspective of a practical navigator sitting in the cheap seats. Fire away boys. In the early 1990's, Greg Walsh, who was the editor of Ocean Navigator Magazine, wrote a rather scathing editorial about the NA tables, suggesting that they were too complex and should be removed from the NA in favour of something simpler. The response from one of the board members of the Navigator's Newsletter (I believe it might have been Doug Davies but cannot remember for sure) was priceless: In addition to countering Mr. Walsh's contention, the letter writer suggested that Mr. Walsh's comments were more worthy of something that had been "written from a barstool". Robert ----- Original Message ----- From: "Geoffrey Kolbe"To: Sent: Sunday, April 08, 2012 2:04 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 > > > > > > __________ Information from ESET Smart Security, version of virus > signature database 7036 (20120407) __________ > > The message was checked by ESET Smart Security. > > http://www.eset.com > > > __________ Information from ESET Smart Security, version of virus signature database 7037 (20120408) __________ The message was checked by ESET Smart Security. http://www.eset.com