NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: 3-Star Fix - "Canned Survival Problem"
From: Greg R_
Date: 2008 Aug 18, 15:31 -0700
From: Greg R_
Date: 2008 Aug 18, 15:31 -0700
--- "Gary J. LaPook"wrote: > BTW, did you ever check my work? I posted the solution to that one in [NavList 5428]: "GPS position for that series of sights is 34�14.4�N / 119�15.9�W, and my Navigator computer program calculates 34�12.6'N / 119�16.5'W (using APs of 34�N and W longitudes to give a whole number of LHA)". Or, if you'd like to me take a look at the (creative) method you used to solve it post a message # and I'll take a look at it. -- GregR --- "Gary J. LaPook" wrote: > BTW, did you ever check my work? > > gl > > Greg R. wrote: > > Assuming you're not being tongue-in-cheek with your solution (and > being > at work I can't verify it right now), regardless of accuracy you > definitely get the Most Unique Solution award (plus an honorary > Navigator Who I'd Most Want To be Shipwrecked With plaque, with gold > clusters). :-) > > > >Heh... I almost wrote the exercise with all of the navigation books > >being lost overboard too, and luckily the intrepid navigator had > >memorized their entire contents - but figured that was a bit too > much > >of a stretch. Now I may have to re-consider that option... ;-) > > > >Assuming you're not being tongue-in-cheek with your solution (and > being > >at work I can't verify it right now), regardless of accuracy you > >definitely get the Most Unique Solution award (plus an honorary > >Navigator Who I'd Most Want To be Shipwrecked With plaque, with gold > >clusters). :-) > > > >-- > >GregR > > > > > > > >--- "Gary J. LaPook" wrote: > > > > > > > >>Being the conscientious navigator that I am, I followed my usual > >>practice of memorizing some data from the 2008 Nautical Almanac so > >>that > >>I would have it available for emergency use. > >> > >>The first thing I memorized was the GHA of Aires at 0000 Z January > 1, > >> > >>2008 which is 100� 01.9' and also remembering that Aires advances > >>59.139' each day. With this information you can calculate GHA Aires > >>for > >>0000 Z on June 9, 2008 which is the 161st day of the year but is > only > >> > >>160 days from January 1st. So multiplying 59.139' times 160 days > >>gives > >>157� 42.2' to which you add the starting value of 100� 01.9' to > come > >>up > >>with the GHA Aires on June 9th at 0000 Z of 257� 44.1'. To this > you > >>add > >>the change of GHA for the time since 0000 Z (3 hours 42 minutes 10 > >>seconds for the Vega shot) by multiplying the time interval by the > >>rate > >>of change of 15.041� per hour making 55� 41.6' making the GHA Aires > >>at > >>the time of the Vega shot of 313 � 25.7'. > >> > >>I also memorized the SHAs and the Declinations of ten of the > >>navigation > >>stars ( nobody could memorize all 57) which should be enough for > >>emergency use as tabulated for July 1st so that the values will be > >>reasonable for the whole year. Fortunately this included the three > >>stars > >>used in this exercise. So now adding the SHA of Vega, 80� 41' we > end > >>up > >>with the GHA of Vega of 34� 06.7' and using the D.R. as the A.P. we > >>get > >>an LHA of 274� 48' and the declination of 38� 47' N. (rounded to > the > >>whole minute) > >> > >>Using these values on my Bygrave slide rule (see attached work > sheet) > >> > >>since I have no tables with me, I computed Hc of 23� 59'. > >> > >>The Hs given was 24� 05.5' Computing the dip correction in my head > of > >> > >>4.5' (the square root of 20 must be between 4 and 5 ) and applying > >>the > >>refraction correction of minus 2 gives an Ho of 23� 59' giving and > >>intercept of zero and an azimuth of 58.1 �. I long ago memorized > >>the > >>refraction table for altitudes above 10� in The Air Almanac and in > >>H.O > >>249, the cutoff values are 63-33-21-16-12-10� , zero above 63, 1 > >>above > >>33, 2 above 21, 3 above 16, 4 above 12 and 5 above 10. > >> > >>I used the same procedure for Spica and Pollux getting another zero > > >>intercept for Pollux, Zn of 290.2� and a 4 NM away for Spica with > a > >>Zn > >>of 171.7�. > >> > >>Since I am on the road I do not have any of my plotting tools with > me > >>so > >>I had to make do with what I found in my briefcase. I used my MB-2A > > >>flight computer since it had an azimuth scale and I used a pad of > >>paper > >>with a right angle at the corner as my straight edge for plotting > the > >> > >>LOPs. I used a tape measure from IKEA to measure the length of the > >>intercept (see photo.) I plotted the LOPs and found the fix by > >>bisecting the three angles giving a fix .4 NM west of the A.P. > (D.R.) > >> > >>and 2.8 NM north of it. (Plotting a fix as a distance from the A.P. > >>like > >>this is common in aerial practice and it is often done on an E-6B.) > > >>Adding the 2.8 NM north to the D.R. latitude gives a fix latitude > of > >>34� > >>16' North. To convert the .4 NM west to a longitude you divide the > >>.4 > >>NM by the cosine of the latitude, .82, to find the difference in > >>longitude of .5' so the fix longitude is 119� 19.5' West (rounded > to > >> > >>either 119� 19' or 20'.) ( I got the cosine of 34� by finding the > >>sine > >>of 56� on the MB-2A sine scale, used for wind correction > >>calculations.) > >> > >>My fix might not be in agreement with others but I used a > refraction > >>table tabulated in whole minutes, I only memorized the stars' > >>positions > >>to the nearest minute and I did not have any plotting tools to use > >>but > >>my position is certainly good enough for emergency navigation and > >>done > >>without an almanac, tables or electrons. > >> > >>(I will have to send the images when Ii figure out how to make them > > >>smaller.) > >> > >>gl > >>1 > >> > >>m_burkes@msn.com wrote: > >> > >> > >> > >>>Captain Lecky would be proud of those dividers ha! Speaking of > >>>interpolation I have found a neat way to get around that pesky DSD > >>> > >>> > >>and > >> > >> > >>>interpolation tables by using the aviation E6B computer or the > >>>equivalent nautical slide rule. Essentially the set > up:d-value/60=d- > >>>correction/declination minutes. Yes the calculator offers the > proof. > >>>Mike Burkes > >>>On Jun 12, 11:44 pm, Anabasi...@aol.com wrote: > >>> > >>> > >>> > >>> > >>>>Thanks for the nice exercise Greg. I literally had to dust off > the > >>>> > >>>> > >> ship's > >> > >> > >>>>Vol III of HO 229 and deflower a Plotting sheet 925 to work this > >>>> > >>>> > >>one out. > >> > >> > >>>>Since I was bereft of electronic gadgets, I did this with a > >>>> > >>>> > >>plotting sheet, > >> > >> > >>>>2 triangles, a pair of dividers, 2 books, a pencil, and small > piece > >>>> > >>>> > >>of scratch > >> > >> > >>>>paper (wouldn't have reams of paper in the Lifeboat). I have > >>>> > >>>> > >>attached a > >> > >> > >>>>picture in to this message with the plot and the tools. > >>>> > >>>>My Lat is a bit lower (plotting or math error?). I used an > assumed > >>>> > >>>> > >> position > >> > >> > >>>>method and HO 229. I had to assume we were drifting and no > >>>> > >>>> > >>current (didn't > >> > >> > >>>>advance or retard the lines). I had not done a full HO 229 > paper > >>>> > >>>> > >>reduction > >> > >> > >>>>of a star in many years, and I had to think a second to remember > >>>> > >>>> > >>how to use > >> > >> > >>>>the interpolation pages on the inside covers for the declination > >>>> > >>>> > >>interpolation. > >> > >> > >>>>I usually whip those off with the calculator. Still, I got > >>>> > >>>> > >>pretty close to > >> > >> > >>>>the computer solutions with Lat 34deg 11.9' N and Longitude > 119deg > >>>> > >>>> > >>16.0'W. > >> > >> > >>>>As to how you would get an Eastern sight on the west coast, you > >>>> > >>>> > >>would have 2 > >> > >> > >>>>options in general. The first would be a back sight. This would > >>>> > >>>> > >>be > >> > >> > >>>>particularly difficult with a regular sextant at such a low > >>>> > >>>> > >>altitude. The other > >> > >> > >>>>option would be to use a bubble sight tube or other artificial > >>>> > >>>> > >>horizon. If you > >> > >> > >>>>were across a bay, you could also use a dip short of the horizon > >>>> > >>>> > >>table. > >> > >> > >>>>That's all I can think of at the moment. > >>>> > >>>>Jeremy > >>>> > >>>>**************Vote for your city's best dining and nightlife. > >>>> > >>>> > >>City's Best > >> > >> > >>>>2008. (http://citysbest.aol.com?ncid=aolacg00050000000102) > >>>> > >>>>gregExerPlot.jpg.JPG > >>>>182KViewDownload > >>>> > >>>>GregExerTools.jpg.JPG > >>>>129KViewDownload > >>>> > >>>> > >>>> > >>>> > >>>> > >>> > >>> > >>> > >>> > >> > >> > > > > > >> > > > > > > > > > > > --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---