|
|
|
|
|||||
|
||||||
Subject: Re: The Complete On-Board Celestial Navigator Second Edition.
From: Peter Fogg (ffive@XXX.XXX)
Date: Sun Aug 28 1977 - 01:10:55 EDT
George Huxtable wrote:
> As long as a navigator is suitably cautious in
> applying Bennett's tables, he can get along fine. Trouble will eventually
> arise if he relies on his assumption of a precision which is achieved only
> some, and not all, of the time. And that's what Peter Fogg is in danger of
> doing.
I don't feel in imminent danger since I accept that the whole process is
approximative.
Nautical celestial navigation has been largely developed for and used by ships.
Compared with a yacht they offer a stable platform with an elevated outlook and an
abundance of space and equipment and devoted officers. Just as well, as they are
also a lot faster.
'The Complete On-Board Celestial Navigator ' has been designed for the needs and
circumstances of small boats, as a back-up method to, for example, GPS.
This does not mean that accuracy and precision are tossed out the window.
Typically a number of options are presented and explained with examples. The user
is encouraged to become familiar with them all.
Here are 2 examples:
1 In the case of azimuth, there are 4 options.
(a) The least accurate comes from the pages of Prediction and Identification.
This is not a criticism, presenting information in tabular form has the
advantages of simplicity and easy access, making them ideal for their task.
Interpolation between adjacent columns is helpful.
(b) Corrected compass bearing, enough said already..
(c) Azimuth tables
(d) Weir diagrams
2 In the case of v and d corrections; these are presented as tables, and also
as factors to 3 decimal places for calculator interpolation. A table is presented
with comparisons of the 2 methods.
Dr Bennett is the former head of the School of Surveying, Faculty of Engineering
at the University of New South Wales.
As such he is no stranger to the concept of precision. He is the co-author of a
book dealing with astro-navigation (the English term) for surveyors. For anyone
interested in this highly precise endeavour it is a fascinating book, if not easy
reading. One part that really caught my attention dealt with (and these are my
words, I don't have the book in front of me) calculating the fix position from
position lines (or LOPs, the American term). This was a topic of great interest to
this list some time ago. Unfortunately I read this book after that great
controversy died down. If I remember correctly, with 3 LOPs from an azimuth range
of less than 180 degrees the fix is predicted to lie outside the triangle.
But 'The Complete On-Board Celestial Navigator' is a different book with a
different aim, to bring together in the one slim and handy package all the
resources an amateur navigator needs for practical celestial navigation.
|