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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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