Next message: Courtney Thomas: "Re: Fwd: Principles and Being Practical"
I just ordered it based on your recommendation.
Courtney
HGWorks - Phil Guerra wrote:
> Courtney,
>
> Susan Powell's book includes HO229 fragments needed to do the exercises, and
> the US Navy site, I gave in the last message has some links to the different
> volumes of the HO 229, and HO249, so either way would work. Have you seen
> the Susan Powell book?
>
> Phil
> ----- Original Message -----
> From: "Courtney Thomas" <>
> To: <>
> Sent: Thursday, September 11, 2003 8:06 PM
> Subject: Re: Fwd: Principles and Being Practical
>
>
>
>>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, no
>>>>>>>>>
> t
>
>>>>>>>>>
>>>>>>>>>
>>>>>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
>>
>>
>
--
Courtney
s/v Mutiny
lying Oriental, NC
