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    Re: Fwd: Principles and Being Practical
    From: Courtney Thomas
    Date: 2003 Sep 11, 20:06 -0500

    Thanks again Phil.
    
    I have the HO 249 set. I just wondered if Susan Howell's book would
    apply equally well to 249 as 229.
    
    Cordially,
    Courtney
    
    
    
    HGWorks - Phil Guerra wrote:
    
    > Basically,
    >
    > The methods are closely related, being different in the tables used to
    > acquire the data in the sight reduction, and some technique variations. The
    > HO 249 is a 3 volume set originally designed for use by aviation navigators,
    > and the HO 229 is an six volume set, with far more solutions.  However, the
    > HO229 is costly and probably not the most widely used by other than the most
    > serious navigators.  That's why short tables, such as Bayless, and Ageton
    > are still used, though not as much with the advent of cheap navigation
    > computers and GPS.
    >
    > Really, though I think you can adapt from either, it just takes finding your
    > way through one of the methods and getting a good feel for it.  Again, I'm
    > sure others could help you assess which one is right for you.  The precision
    > of the HO 229 is probably more than you need on a regular basis, but you
    > never know what you miss until you don't have it.  Check out the US Navy
    > site to read more about it, and take a look at their great documentation and
    > computer utilities at this site:
    > http://aa.usno.navy.mil/publications/
    >
    > Still if you need to move quickly, you may need to contact a Sailing /
    > Navigation School.  My desk rarely moves, so I've got a little more time to
    > play with than you, I suspect.
    >
    > Take care,
    >
    > Phil
    >
    >
    > ----- Original Message -----
    > From: "Courtney Thomas" 
    > To: 
    > Sent: Tuesday, September 09, 2003 5:22 AM
    > Subject: Re: Fwd: Principles and Being Practical
    >
    >
    >
    >>Phil,
    >>
    >>Thank you for the book information.
    >>
    >>What is the difference between HO 249 and HO 229 techniques ?
    >>
    >>Cordially,
    >>Courtney
    >>
    >>
    >>
    >>HGWorks - Phil Guerra wrote:
    >>
    >>
    >>>Sorry for the tardy reply.  Yes, I've got Mary Blewitt's book, as well,
    >>>although, I've misplaced it.  I found it to be a really good reference,
    >>>
    > and
    >
    >>>it's compact size made it easy to take to work for reading on my breaks.
    >>>
    > If
    >
    >>>I remember correctly, she uses the H.O.249 to do sight reductions.  Other
    >>>methods are given some mention, but not really examined.
    >>>
    >>>The book I really worked through was Susan Powell's Practical Celestial
    >>>Navigation.   It's more like a workbook giving lots of examples and
    >>>solutions.  She uses the H.O. 229 for her sight reduction work.  I think,
    >>>the method you use depends on your specific needs.  What's most important
    >>>
    > is
    >
    >>>that you know your method down pat, and have a backup method or two.
    >>>
    >>>I know many of the list's group could tell you more, I've no real
    >>>
    > experience
    >
    >>>in actual on-board CN.  I'm just in awe and admire all who are able to do
    >>>it.  I enjoy the mechanics of the process of CN because it emcompasses so
    >>>many of my interests into an area that uses them all.  Good luck to you.
    >>>
    >>>Phil Guerra
    >>>www.hgworks.com
    >>>----- Original Message -----
    >>>From: "Courtney Thomas" 
    >>>To: 
    >>>Sent: Sunday, September 07, 2003 4:29 PM
    >>>Subject: Re: Fwd: Principles and Being Practical
    >>>
    >>>
    >>>
    >>>
    >>>
    >>>>Phil,
    >>>>
    >>>>Thanks so much for the fulsome reply.
    >>>>
    >>>>I am a non-armchair sailor and am trying to find the best, i.e. easiest
    >>>>that meets real world navigational needs, CN technique rather than a
    >>>>more abstract interest but thank goodness for such.
    >>>>
    >>>>I suspect Newton would've probably been a poor farmer but gratefully so.
    >>>>
    >>>>For now I just don't want to waste time/energy learning one technique to
    >>>> later learn that it was not the most suitable.
    >>>>
    >>>>It's not that it is intrinsically uninteresting it's that my agenda is
    >>>>reversed, at this time.
    >>>>
    >>>>Incidentally, are you familiar with Mary Blewitt's book ? If yes, what
    >>>>do you think of it ?
    >>>>
    >>>>Cordially,
    >>>>Courtney
    >>>>
    >>>>
    >>>>
    >>>>HGWorks - Phil Guerra wrote:
    >>>>
    >>>>
    >>>>
    >>>>
    >>>>>The Ageton method is not discussed in Bennett's book.  It is really a
    >>>>>compact treatment of the subject designed for use on-board.  As far as
    >>>>>
    >>>>>
    >>>>>
    >>>the
    >>>
    >>>
    >>>
    >>>>>best explanation of the method, I never really found anything more than
    >>>>>
    >>>>>
    >>>>>
    >>>his
    >>>
    >>>
    >>>
    >>>>>book, "Manual of Celestial Navigation" in print.  I found the book by
    >>>>>
    >>>>>
    >>>>>
    >>>chance
    >>>
    >>>
    >>>
    >>>>>in a used book store, but have seen it offered on Ebay for around an
    >>>>>
    >>>>>
    >>>>>
    >>>average
    >>>
    >>>
    >>>
    >>>>>price of 10-20 dollars (US).  Unfortunately, the book is not really a
    >>>>>'teaching guide' but probably was used to supplement classroom
    >>>>>
    >>>>>
    >>>>>
    >>>instruction.
    >>>
    >>>
    >>>
    >>>>>Another, offshoot of the method was put forward by Allan E. Bayless,
    >>>>>"Compact Sight Reduction Table", again using a slight modification of
    >>>>>Ageton's method.  This book is out of print as well, and I found a copy
    >>>>>
    >>>>>
    >>>>>
    >>>on
    >>>
    >>>
    >>>
    >>>>>Ebay.
    >>>>>
    >>>>>My expanding CN library includes, Bowditch, Dutton's Navigation &
    >>>>>
    >>>>>
    >>>Piloting,
    >>>
    >>>
    >>>
    >>>>>which all refer to the method, but really do not give it much clarity,
    >>>>>
    >>>>>
    >>>>>
    >>>at
    >>>
    >>>
    >>>
    >>>>>least for me coming in as a novice.  This lead me to ask questions on
    >>>>>
    >>>>>
    >>>>>
    >>>this
    >>>
    >>>
    >>>
    >>>>>list about it.  I did find a good description on a referenced web site
    >>>>>http://home.t-online.de/home/h.umland/page3.htm, by Henning Umland,
    >>>>>
    >>>>>
    >>>>>
    >>>which
    >>>
    >>>
    >>>
    >>>>>cleared up most of the questions regarding how to use it, as his
    >>>>>
    >>>>>
    >>>>>
    >>>authored,
    >>>
    >>>
    >>>
    >>>>>"The Ageton Tables", gives some good description of the method,
    >>>>>
    >>>>>
    >>>>>
    >>>examples,
    >>>
    >>>
    >>>
    >>>>>and solutions.  Umland did expand the method a bit by providing a new
    >>>>>
    >>>>>
    >>>>>
    >>>set of
    >>>
    >>>
    >>>
    >>>>>tables to give it more accuracy.  The site is a great starting point
    >>>>>information regarding CN in general, and he has a lot of very useful CN
    >>>>>links.   After going through Umland's article, I was able to go back to
    >>>>>
    >>>>>
    >>>>>
    >>>the
    >>>
    >>>
    >>>
    >>>>>Bowditch and Dutton books and understand the terse descriptions and
    >>>>>
    > work
    >
    >>>>>
    >>>the
    >>>
    >>>
    >>>
    >>>>>examples yielded the solutions.
    >>>>>
    >>>>>I've begun work on using the information gleamed from all of my sources
    >>>>>
    >>>>>
    >>>>>
    >>>to
    >>>
    >>>
    >>>
    >>>>>produce a web site to teach the method, but it's stalled at present due
    >>>>>
    >>>>>
    >>>>>
    >>>to
    >>>
    >>>
    >>>
    >>>>>other responsibilities.  However, if you need help understanding it,
    >>>>>
    > let
    >
    >>>>>
    >>>me
    >>>
    >>>
    >>>
    >>>>>know via my existing web site www.hgworks.com using the Contact Us
    >>>>>
    > page.
    >
    >>>>>
    >>>I
    >>>
    >>>
    >>>
    >>>>>found that building the web application to use Ageton gave great
    >>>>>
    >>>>>
    >>>>>
    >>>accuracy
    >>>
    >>>
    >>>
    >>>>>with the mathematical model, and using the table values gave it such
    >>>>>accuracy that it was, I believe in use for over 30 years, before
    >>>>>
    > falling
    >
    >>>>>
    >>>out
    >>>
    >>>
    >>>
    >>>>>of favor, due to technological advancements.  There are questions of
    >>>>>accuracy in Azimuth calculation, and it is documented.
    >>>>>
    >>>>>Although, I'm a 'deskbound navigator', others who I've come into
    >>>>>
    > contact
    >
    >>>>>with on this list, indicate that the methods and books are still used
    >>>>>on-board, which is testament to the value of the work done.
    >>>>>
    >>>>>Hope this helps,
    >>>>>
    >>>>>Phil Guerra
    >>>>>www.hgworks.com
    >>>>>
    >>>>>----- Original Message -----
    >>>>>From: "Courtney Thomas" 
    >>>>>To: 
    >>>>>Sent: Sunday, September 07, 2003 4:15 AM
    >>>>>Subject: Re: Fwd: Principles and Being Practical
    >>>>>
    >>>>>
    >>>>>
    >>>>>
    >>>>>
    >>>>>
    >>>>>>Is Ageton's method described in Bennett's book ? If not, where is the
    >>>>>>best exegesis of it, please ?
    >>>>>>
    >>>>>>Thank you.
    >>>>>>
    >>>>>>Dr. Geoffrey Kolbe wrote:
    >>>>>>
    >>>>>>
    >>>>>>
    >>>>>>
    >>>>>>
    >>>>>>>George Huxtable has pointed up a potential problem with the azimuth
    >>>>>>>
    >>>>>>>
    >>>>>>>
    >>>>>>>
    >>>>>tables
    >>>>>
    >>>>>
    >>>>>
    >>>>>
    >>>>>>>in George Bennett's book "The Complete On-board Celestial Navigator".
    >>>>>>>
    >>>>>>>
    >>>>>>>
    >>>He
    >>>
    >>>
    >>>
    >>>>>>>has shown that there can be errors in computed azimuth of (at least)
    >>>>>>>
    > 15
    >
    >>>>>>>degrees where the celestial body is that sort of distance away from
    >>>>>>>
    > the
    >
    >>>>>>>prime vertical.
    >>>>>>>
    >>>>>>>Peter Fogg tells us that this is "nit-picking" and that in any case,
    >>>>>>>
    >>>>>>>
    >>>>>>>
    >>>the
    >>>
    >>>
    >>>
    >>>>>>>book tells us that, "In extreme cases the table should be
    >>>>>>>
    > interpolated
    >
    >>>>>>>
    >>>>>>>
    >>>>>when
    >>>>>
    >>>>>
    >>>>>
    >>>>>
    >>>>>>>observations have been made in the vicinity of the prime vertical."
    >>>>>>>
    >>>>>>>I do not have the second edition, only the 1999-2003 edition where
    >>>>>>>
    > this
    >
    >>>>>>>phrase is not present. Perhaps Peter can tell us just what "extreme"
    >>>>>>>
    >>>>>>>
    >>>>>>>
    >>>>>>>
    >>>>>means
    >>>>>
    >>>>>
    >>>>>
    >>>>>
    >>>>>>>in this context? When do we know we are in an extreme case? George
    >>>>>>>
    > also
    >
    >>>>>>>posed some other pertinent questions to Peter and I too would be
    >>>>>>>
    >>>>>>>
    >>>>>>>
    >>>>>>>
    >>>>>interested
    >>>>>
    >>>>>
    >>>>>
    >>>>>
    >>>>>>>to see the answers...
    >>>>>>>
    >>>>>>>I also wonder just how much of a problem it would cause having your
    >>>>>>>near-prime-vertical azimuths off by around 15 degrees? For a cluster
    >>>>>>>
    > of
    >
    >>>>>>>star sights, say, a prudent navigator would also be taking sights
    >>>>>>>
    > from
    >
    >>>>>>>objects far away from the prime vertical (to get useful angular
    >>>>>>>
    >>>>>>>
    >>>>>>>
    >>>>>>>
    >>>>>separation)
    >>>>>
    >>>>>
    >>>>>
    >>>>>
    >>>>>>>and this would tend to mitigate any problems due to bad
    >>>>>>>
    >>>>>>>
    >>>>>>>
    >>>>>>>
    >>>>>near-prime-vertical
    >>>>>
    >>>>>
    >>>>>
    >>>>>
    >>>>>>>azimuths. The inaccuracy of the tables near the prime vertical are
    >>>>>>>
    > also
    >
    >>>>>>>mitigated by being able to assess independently (in many cases) in
    >>>>>>>
    >>>>>>>
    >>>>>>>
    >>>which
    >>>
    >>>
    >>>
    >>>>>>>azimuth quadrant the celestial object sits.
    >>>>>>>
    >>>>>>>If your estimated position is pretty close (say, within 10 nautical
    >>>>>>>
    >>>>>>>
    >>>>>>>
    >>>>>>>
    >>>>>miles)
    >>>>>
    >>>>>
    >>>>>
    >>>>>
    >>>>>>>to your actual position then I cannot think of any circumstances
    >>>>>>>
    > where
    >
    >>>>>>>
    >>>it
    >>>
    >>>
    >>>
    >>>>>>>would significantly affect the sort of accuracy we would expect from
    >>>>>>>
    > CN
    >
    >>>>>>>
    >>>>>>>
    >>>>>in
    >>>>>
    >>>>>
    >>>>>
    >>>>>
    >>>>>>>a small boat at sea, which is the sort of user the book was aimed at
    >>>>>>>
    > in
    >
    >>>>>>>
    >>>>>>>
    >>>>>the
    >>>>>
    >>>>>
    >>>>>
    >>>>>
    >>>>>>>first place. I have not thought deeply on this problem and I would
    >>>>>>>appreciate the thoughts of other listers who will have greater
    >>>>>>>
    > insight
    >
    >>>>>>>
    >>>on
    >>>
    >>>
    >>>
    >>>>>>>this problem than I.
    >>>>>>>
    >>>>>>>The "short" method of sight reduction used by Bennett is popular
    >>>>>>>
    >>>>>>>
    >>>>>>>
    >>>because
    >>>
    >>>
    >>>
    >>>>>>>the computed altitude can be arrived at quite quickly. But a
    >>>>>>>
    > different
    >
    >>>>>>>procedure is required to calculate an azimuth and this rather takes
    >>>>>>>
    > the
    >
    >>>>>>>gilt off this method. Ageton's method, by contrast, requires more
    >>>>>>>
    > steps
    >
    >>>>>>>
    >>>>>>>
    >>>>>to
    >>>>>
    >>>>>
    >>>>>
    >>>>>
    >>>>>>>get to the calculated altitude, but the azimuth then drops out very
    >>>>>>>
    >>>>>>>
    >>>>>>>
    >>>>>>>
    >>>>>quickly
    >>>>>
    >>>>>
    >>>>>
    >>>>>
    >>>>>>>and is accurate. Azimuth quadrant ambiguities are also easily
    >>>>>>>
    > resolved.
    >
    >>>>>>>Too, only one set of tables is required for the Ageton method.
    >>>>>>>
    >>>>>>>Geoffrey Kolbe
    >>>>>>>
    >>>>>>>
    >>>>>>>-------------------8<---------------------
    >>>>>>>From: George Huxtable
    >>>>>>>The problem with these azimuth tables ...
    >>>>>>>is not in their ambiguity, but in their inaccuracy, and that
    >>>>>>>
    > inaccuracy
    >
    >>>>>>>
    >>>>>>>
    >>>>>is
    >>>>>
    >>>>>
    >>>>>
    >>>>>
    >>>>>>>exactly what I have complained about. And there is not one word, not
    >>>>>>>
    >>>>>>>
    >>>>>>>
    >>>even
    >>>
    >>>
    >>>
    >>>>>a
    >>>>>
    >>>>>
    >>>>>
    >>>>>
    >>>>>>>hint, in the book that major errors in azimuth can occur, for certain
    >>>>>>>observations in a VERY wide swathe around East or West.
    >>>>>>>-------------------8<---------------------
    >>>>>>>>From Peter Fogg
    >>>>>>>
    >>>>>>>Inserted in second edition is . "In extreme cases the table should be
    >>>>>>>interpolated when observations have been made in the vicinity of the
    >>>>>>>
    >>>>>>>
    >>>>>>>
    >>>>>>>
    >>>>>prime
    >>>>>
    >>>>>
    >>>>>
    >>>>>
    >>>>>>>vertical and/or LHA, declination and latitude require substantial
    >>>>>>>
    >>>>>>>
    >>>>>>>
    >>>>>>>
    >>>>>rounding
    >>>>>
    >>>>>
    >>>>>
    >>>>>
    >>>>>>>off before using the table. When in doubt use the Weir diagrams.
    >>>>>>>
    >>>>>>>In practice you could happily sail across an ocean and never notice
    >>>>>>>
    >>>>>>>
    >>>>>>>
    >>>this
    >>>
    >>>
    >>>
    >>>>>>>supposed problem, particularly by following the common sense approach
    >>>>>>>outlined previously. With nav. it it often a case of one system
    >>>>>>>
    >>>>>>>
    >>>>>>>
    >>>checking
    >>>
    >>>
    >>>
    >>>>>>>another. In fact taking sights and working out a fix is a check on
    >>>>>>>
    > the
    >
    >>>>>>>basic tool of running a DR.
    >>>>>>>
    >>>>>>>If the whole book has been subjected to the same searching criticism
    >>>>>>>
    >>>>>>>
    >>>>>>>
    >>>and
    >>>
    >>>
    >>>
    >>>>>>>this rather inconsequential nit-pick is the only flaw found, then it
    >>>>>>>
    > is
    >
    >>>>>>>really a back-handed compliment to the book as a whole. A ferocious
    >>>>>>>
    >>>>>>>
    >>>>>>>
    >>>>>>>
    >>>>>critic
    >>>>>
    >>>>>
    >>>>>
    >>>>>
    >>>>>>>seems to think the rest works just fine.
    >>>>>>>
    >>>>>>>Border Barrels Ltd., Newcastleton, Roxburghshire, TD9 0SN, Scotland.
    >>>>>>>Tel. +44 (0)13873 76253 Fax. +44 (0)13873 76214.
    >>>>>>>
    >>>>>>>
    >>>>>>>
    >>>>>>>
    >>>>>>>
    >>>>>>>
    >>>>>>--
    >>>>>>Courtney Thomas
    >>>>>>s/v Mutiny
    >>>>>>lying Oriental, NC
    >>>>>>
    >>>>>>
    >>>>>>
    >>>>>>
    >>>>>>
    >>>>--
    >>>>Courtney
    >>>>s/v Mutiny
    >>>>lying Oriental, NC
    >>>>
    >>>>
    >>>>
    >>>>
    >>>
    >>>
    >>--
    >>Courtney Thomas
    >>s/v Mutiny
    >>lying Oriental, NC
    >>
    >>
    >
    
    
    --
    Courtney
    s/v Mutiny
    lying Oriental, NC
    
    
    

       
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