NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Lat/Lon by "Noon Sun"
From: George Huxtable
Date: 2009 Apr 14, 18:19 +0100
From: George Huxtable
Date: 2009 Apr 14, 18:19 +0100
Although Geoffrey Kolbe's posting, in [7837] , appears to differ greatly with my own, it seems to me that the difference between us is rather less than he makes out. I have no great argument against "navigation around noon", as long as it's kept in its proper place. It is indeed a valid tool in the navigator's workbox, and under the right circumstances can provide useful answers, as long as its deficiencies are recognised. It is, in almost every respect, inferior to traditional position-line navigation, with only one thing to be said in its favour; that it is intellectually undemanding. If it's taught to students as part of a syllabus that includes all the other necessary stuff for proper navigation, then well and good, as I said before. Geoffrey wrote- "Having graduated from the "Frank Reed school" and my interest aroused, I then went on to gain "a rounded understanding of position lines and sight reduction, how to read a nautical almanac, how to use the Moon or take a twilight round of star observations..." I ask Geoffrey whether, before going on to gain that "rounded understanding", he considered himself competent to "navigate successfully and safely around the world". I hope not, because if he did, that's where danger lies. Geoffrey continued- "Frank's point, though, is that it was not necessary to go on and do the post-grad course to be able to navigate successfully and safely around the world - provided the limitations of the method are born in mind. But that is true whatever method is used." What I complain of, in Frank's many postings on this topic, is that such limitations have been minimised, or dismissed, and it has fallen to sceptics such as me to point them out. My interpretation of Frank's postings on this subject has been that it is being proposed as an alternative to position-line navigation, not as an adjunct to it. If I have got that wrong, I hope Frank will put me right, and he would then deserve an apology. It would be interesting to see what a syllabus for a Frank Reed navigation course would include. Geoffrey asks- And why should a generation of navigational incompetents arise because one person chooses this particular method from the long menu available of CN methods and finds it to his liking? To say that they will "quickly become lost at sea" by being such a "one club golfer" is gross exaggeration George, as I am sure you know. "Celestial Navigation" is actually done as a check on dead reckoning. If the sun does not shine for a few days, it just means the uncertainty in your position grows. It does not result in you being "lost at sea". Living where Geoffrey does, in the Scottish Borders, that attitude surprises me. His climate is similar to mine. We get cloudy skies. The Sun is available only about a third of our daytime (at my guess). A celestial navigator gets by, by snatching appearances of the Sun within broken cloud, when he can. The days when the Sun appears for an unbroken hour around midday are few and far-between, and this is a common state of affairs in higher latitudes. Things may be different in the Med, in Florida and the Caribbean. Geoffrey may think that DR will substitute, but not to a navigator entering the Western Approaches after an Atlantic crossing. He needs an observation. Geoffrey wrote- "I think that the point was made four years ago that in the latitudes at which, and the seasons in which, people usually go sailing recreationally, Frank's claimed accuracy was reasonable." Aha! Is that an accepted limitation, then? How are those limits defined? Prospective users should be told. "Frank did say that if an analemma is used for the equation of time, its scale should be "sufficient".". No. The words were these, about the Nautical Almanac- "you don't need one at all --only a short table of declination and equation of time, possibly graphed as an "analemma" perhaps " Let's think about that. If Frank is going to meet his claim of no more than +/- 2 minutes in latitude, I think he and I would agree that any error greater than 1 minute in predicted declination would be unacceptable. Declination varies over a range of 47�, and changes at up to 1' in each hour. If that's going to come from an analemma, it would be necessary to read it to one part in 3000 of its span, and to read off a particular date-and-time, to the nearest hour, around a loop which occupies a year. Can't be done. George. contact George Huxtable, at george@hux.me.uk or at +44 1865 820222 (from UK, 01865 820222) or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---