NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Principles and Being Practical
From: Peter Fogg
Date: 2003 Sep 6, 08:47 +1000
From: Peter Fogg
Date: 2003 Sep 6, 08:47 +1000
----- Original Message ----- From: "George Huxtable" To those of us who have > done all that introductory stuff, years ago, some of the fine-points and > abstruse-topics and historical-questions are of great interest, and the > Nav-L list is our method of communicating with each other about it. Would > Peter Fogg deny us that? No. And I enjoy them myself. Don't miss the point. As for the Azimuth Tables, there are instructions in the book to be followed to deal with the potential problems when the bearing is close to 90 or 270 degrees. A common sense approach, remembering that the whole idea is to keep things simple on-board, is to give the tables a miss and use another method (provided) in these rare enough cases. There is no need to make a mountain out of a molehill. To say they are 'VERY bad' is a gross exaggeration, at the VERY worse they might be only slightly naughty. When taking sights the hand bearing compass is around my neck, and the compass bearing of the star or planet noted with the other data (I might need the corrected [true] bearing or azimuth to find out which body it is, through the Prediction and Identification Tables). This corrected compass bearing is accurate enough to use for plotting a sight, being out by a degree or two makes little enough difference to the LOPs, and thus the fix, in most cases. So the Azimuth Tables or the Weir Diagrams are mainly useful as a checking tool. Working the other way, knowing the azimuth accurately, is useful to check for compass deviation, the particular effects of each individual boat that alter the compass reading. The advantages, in most cases, of having simple 'look up' tables immediately providing an azimuth accurate enough for the purpose more than outweighs any theoretical shortcoming they may have in some extreme example. So with a common sense and practical approach one can approach the Azimuth Tables with calm and confidence. Its a bit of a non-issue.