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Re: Fwd: Principles and Being Practical
From: Courtney Thomas
Date: 2003 Sep 11, 23:12 -0500
From: Courtney Thomas
Date: 2003 Sep 11, 23:12 -0500
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