03-06-2018, 08:09 AM
(03-04-2018, 08:54 AM)wannathermal Wrote:Bob, sorry for the delay. My calcs. results(03-04-2018, 07:42 AM)Rumata Wrote:(03-03-2018, 02:51 PM)wannathermal Wrote: I think the instructions for Sight Reductions needs to have something like the following:Greetings, Wannathermal.
* Assumed Position for east longitude use DR longitude integral degree plus 60'-GHA minutes for the minutes, If you are at 35° east and the GHA minutes are 33' then AP is E35° 27' (60'-33'=27')
The instructions work for West.
Your suggestion makes sense. But I use ( as an exercise, of course) very simple method :
For the West, assumed longitude , which I use to calculate LHA is equal to the DR longitude in degrees and minutes equal to the minutes of GHA. To make LHA even. For instance, Dr lat. 26 deg. 31 min. N, Dr long. 90 deg. 55.2 min. W, GHA sun 52 deg. 38.1 deg min Now, Assumed long. is 90 deg. 38.1 min. Therefore, LHA =90.38.1 - 52. 38.1= 38-0 East.
East version, use the same approach just to make sure LHA is even. Well, need to admit the fix was never within 2 miles. Always a little bit more.
Anyway, it works for me.
Again, thanks for the interesting approach.
Rumata
What is your Ap for Eastern DR's? Could you show an example with a plot. I like the ease of your approach but I have found that the plotted LOP can be up to a degree off if you round the Ap longitude the wrong way.
Bob (always looking for the easier way) McDowell
Just to be clear, Ap (Assumed position) is not the same as DR (Ded Reckoning), nor with the intercept method should it be. DR is the position of the vessel calculated using speed, time and course from your last fix. Ap is a position derived through GHA and DR Lat and Lon using the whole degree integer for Lat and the whole degree integer with the minutes derived through addition or subtraction.
When using the tables it is important to get the Ap longitude correct so your LOP bisects the azimuth of the celestial object and your DR (within 5-10 miles)
Rumata, if your approach works within 5 miles then keep up the great work.
As an exercise please reduce and plot the following to check the different Ap formulas discussed above. In this case the daily running sun fix was within 2 miles of the DR positions.
17 Feb 2018 (UT) 12:18:50 13:40 15:32
DR Lat N38°09' N38°02' N37°54'
DR Long E15°38' E15°37 E15°46'
HO HS corrected 37°35.5' 29°25.5' 110°21'
Again, these numbers are from the sights taken aboard during our last trip from Les Sable d'Olonne on the Atlantic French coast to Sukosan, Croatia. A cold but great trip. We stayed in between the nastier weather and averaged 7.5 knots for the whole trip.
GMT 12:18:50
GHA 361-13-1
Decl. S11-54-0
LHA 17 deg (GHA-360+Long. assumed=361-13-1-360+15-46.9=17 deg)
Long. assumed=15-46.9
Pub.229
Hc=38-28.9, d=-57.4, Z=158.9
Hc corrected=38-28-9-51.5=37-37.4
Zn=360--158.9=201.1
Intercept-37-37.4-37-35-5=1.9 (away)
For LOP1
Lat.assumed=39N, Long. assumed 15-46-9E, Intercept=1.9 (away), Zn=201.1
===================================================
GMT 13:40, 2/17/2018
GHA 21-30.9
Decl.S11-53.2
LHA=37 deg.
Long assumed =15-29.1 E (approach is the same as in calc aboive. To make LHA even)
Hc. corrected=29-19-2, (30-01.2- 0-42=29-19.2)
d=--50.3
Z=137
Zn=223
intercept=29-25.5-29-19.2=6.3 (to)
For LOP2
Lat.ass.38N, Long. assumed 15-29.1, intercept=6.3 (to), Zn=223
=======================================================
GMT 15:32, 2/17/2018
GHA 49-30.9
Decl. S11-51.4
LHA=GHA+long assumed=49-30.9+15-29.1=65
LHA=65 deg.
Long. assumed 15-29.1E
Hc=12-05.4,
d=-41.1
Hc corrected=12-05.4-0-35*=11-30.4
Z=114.5
Zn=245.5
*0.35- ( this number is from Tabl;e 6 of NA, Correction to TAbulated Altitude for minutes of declination)
Intercept= 11-30.9-11-21=9.4 (away)
For LOP 3
Lat.assumed 38 N, Long. assumed 15-29-1, intercept=9.4 (away), Zn=245.5
===============================================
Result
MPP Lat. 37-51N, Long. 15-45 E
I don't provide the photo/scan of plot because can't make the image of the plotting sheet.
Thanks for following ;>