NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Oops, forget what I said about forgetting Hc
From: Joe Shields
Date: 2000 Feb 29, 8:40 AM
From: Joe Shields
Date: 2000 Feb 29, 8:40 AM
oops, forget what I said about forgetting Hc. With the resulting (calculated) Hc, you can subtract it from 90 to get the distance in nautical miles from source to destination (each degree = 60 nm, each minute = 1 nm). -- Joe > ---------- > From- Joe Shields[SMTP:jshields@POST-GAZETTE.COM] > Reply To: Navigation Mailing List > Sent: Tuesday, February 29, 2000 10:25 AM > To: NAVIGATION-L@LISTSERV.WEBKAHUNA.COM > Subject: Re: Figuring Course given Lat/Long of destination > > Forget Hs and Hc and any sight corrections. Forget your sextant. Forget > what time it is. This is just dealing with the theoretical side of things > starting with latitude, declination, and local hour angle (LHA). Instead > of looking up GHA and Declination from your Nautical Almanac (or whatever) > and then computing LHA from the diff between GHA and your starting > Longitude, just take the difference between starting long. and destination > long. to get LHA. Substitute destination latitude for Declination, and > then > do the trig. or sight reduction. Of course part of the problem might be > HO > 249 which makes you use an AP (assumed position) instead of allowing a DR > lat/long. I use HO 211, which allows me to use my actual lat/long. At > any > rate, the point still needs to be emphasised, that this will only give you > a > bearing to start off with. To continue following a great circle route, > you > would need to recompute a Zn from other intermediate points along the way, > creating waypoints. > > -- Joe Shields > > > ---------- > > From- Ed Kitchin[SMTP:edk@DREAMSCAPE.COM] > > Reply To: Navigation Mailing List > > Sent: Monday, February 28, 2000 6:47 PM > > To: NAVIGATION-L@LISTSERV.WEBKAHUNA.COM > > Subject: Re: Figuring Course given Lat/Long of destination > > > > Thank you, Tony. I'll check my old Bowditch and look for the tables, and > > compare to the construction method to compare results. Meanwhile another > > writer stated that the great circle course could be found by " using a > > regular sight reduction table, substituting the lat./long of destination > > as > > the GP of a heavenly body." He then said to "crank the handle" and get > the > > Zn as your great circle course. Now...I can do celestial nav. thanks to > > recently taken courses using HO 249, or the electronic calculator. I am > > trying to grasp this other guy's concept here. Seems though he is asking > > me > > to work backward through the process, given that sight reduction is to > > OBTAIN the GP, your distance off, and the Zn. Excuse my ignorance, but I > > can't grasp how to do that. What would you use then for the Hs, and what > > corrections would you apply? OR!!! (I just had this idea) You could > enter > > HO > > 249 with the arguments: lat. of destination, and long. of dest. as > > declination, to obtain Zn - - but you would STILL need a corrected > > altitude > > (Hc). I have no idea. Would you help a rank beginner out with this one? > > Thank you. > > > > Ed Kitchin > > ----- Original Message ----- > > From- "Tony"> > To: > > Sent: Monday, February 28, 2000 6:14 PM > > Subject: Re: Figuring Course given Lat/Long of destination > > > > > > > Ed: > > > > > > Well, not quite. I was really encouraging you to use the Bowditch > > > table methods. If you really want to plot this on a UPS what you > > > describe would be satisfactory. > > > > > > Do you have UP sheets for those latitudes? If not you can construct > > > your own constant latitude sheet using Lo divisions as cosine of mid > lat > > > in paper dimensions. > > > > > > Tony > > > > > > Ed Kitchin wrote: > > > > > > > > Thank you, Tony. In other words, I could construct a solution on the > > univ. > > > > plotting sheet, as I mentioned, but use the mean of departure, and > > > > destination latitudes, and that would work? Thank you. > > > > > > > > Ed > > > > ----- Original Message ----- > > > > From- "Tony" > > > > To: > > > > Sent: Sunday, February 27, 2000 9:00 PM > > > > Subject: Re: Figuring Course given Lat/Long of destination > > > > > > > > > Ed: > > > > > > > > > > When you say that "there is the error of the Macerator thing", can > > you > > be > > > > > more specific? Did you use Bowditch Mercator sailing by tables? > > This > > > > > should work out OK. > > > > > > > > > > Actually, just using Plane sailing with mid-latitude should be > quite > > close > > > > > because the distance is relatively short; only earth eccentricity > is > > > > ignored. > > > > > > > > > > Why the problem suggests also GC (great circle) does not make much > > sense. > > > > > There would be less than a mile difference. I did check the > results > > by > > > > > computer and they are OK. [ Sometimes they are not. ;) ] > > > > > > > > > > Tony in San Francisco > > > > > > > > > > > > > > > > Ed Kitchin wrote: > > > > > > > > > > > > An interesting problem appears in the latest issue of "Ocean > > Navigator" > > > > Which asks that you figure > > > > > > the course to a destination given origination and destination. > It > > would > > > > seem easy to determine the > > > > > > difference in lat. (The destination was over several degrees of > > lat.), > > > > but deg. of long. differ in > > > > > > length as you change lat. One could simply take the mean of the > > two > > > > given long. and use that, but > > > > > > that bothers me as not being all that accurate. There is the > error > > of > > > > the Macerator thing. You > > > > > > could use universal plotting sheets and construct using a > vertical > > > > representing diff./lat., then > > > > > > draw a horizontal from the top of the lat. fig., representing > the > > long. > > > > at the destination, and > > > > > > draw a hypotenuse as the course line. (???) Are there any > > mathematicians > > > > out there to > > > > > > give me a good formula to learn for this task? Thank you. > > > > > > > > > > > > Ed Kitchin > > > > > > > > > > >