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    Re: Fwd: Principles and Being Practical
    From: Phil Guerra
    Date: 2003 Sep 11, 18:15 -0500

    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
    >
    
    
    

       
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