AP in the east.

[wannathermal]

I think the instructions for Sight Reductions needs to have something like the following:

*  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.

[CarlosPindle]

I'm in the Western & Northern hemisphere and haven't had any experience in working an Eastern longitude problem.

Wannathermal, could you give us an example for better clarification? Ap only is used when the LOP plot is done. DR longitude is your estimated position.

Thanks,

Carlos

[wannathermal]

I'm in the Western & Northern hemisphere and haven't had any experience in working an Eastern longitude problem.

Wannathermal, could you give us an example for better clarification?  Ap only is used when the LOP plot is done.  DR longitude is your estimated position.

Thanks,

Carlos




Carlos

Well since for me the object of the exercise is to, using the Nautical Almanac and HO249 or 229)  find my position (or for my students to plot the boats actual position) underway Ap is an important component of their site reductions, probably the most important component, get it wrong and your fixes won't work although everything looks good.

So, on Feb 18, 2018 @ 135730 UT 
DR N39°33' E 18°05'course 041T @ 7.5kn (our actual position, approaching the heel of Italy in near gale condition ) 
GHA 25°54' 
So the LHA is 43°59' rounded up to 44°
Assumed Longitude is 18°06' ( longitude integral degree plus 60'-GHA minutes for the minutes)
Assumed Latitude is 39°

My LOP, see attached, went right through my DR and an afternoon running fix was within 2 miles. 

I hope this explains my concern with the instructions.

---

I'm in the Western & Northern hemisphere and haven't had any experience in working an Eastern longitude problem.

Wannathermal, could you give us an example for better clarification?  Ap only is used when the LOP plot is done.  DR longitude is your estimated position.

Thanks,

Carlos




Carlos

Well since for me the object of the exercise is to, using the Nautical Almanac and HO249 or 229)  find my position (or for my students to plot the boats actual position) underway Ap is an important component of their site reductions, probably the most important component, get it wrong and your fixes won't work although everything looks good.

So, on Feb 18, 2018 @ 135730 UT 
DR N39°33' E 18°05'course 041T @ 7.5kn (our actual position, approaching the heel of Italy in near gale condition ) 
GHA 25°54' 
So the LHA is 43°59' rounded up to 44°
Assumed Longitude is 18°06' ( longitude integral degree plus 60'-GHA minutes for the minutes)
Assumed Latitude is 39°

My LOP, see attached, went right through my DR and an afternoon running fix was within 2 miles. 

I hope this explains my concern with the instructions.

I need to add;

DR is our Estimated position derived from our last fix using speed and course, this can also be our EP.
Ap is the Assumed Longitude and Assumed Latitude used to plot the intercept.
Ap is the assumed position

[c_davidson]

Most instructive, Wannathermal.

I had been confused as to whether this discussion was about DR or Ap or plotting an LOP. Now I understand that when determining the Ap longitude for plotting in the Eastern hemisphere that we must do the following, and please tell me if I'm wrong;

In Eastern longitudes LOP Ap longitude is determined as follows;

- To get Ap longitude take your DR longitude add (0°60' minus minutes of GHA)

So in your real example above the formula would look like this;

18° + (0°60' - 0°54') = 18° 06' (which will be the Ap longitude)

Please, would you tell us if there are exceptions to this rule, such as if GHA minutes were less than 30?

Nice work!

Clen

[Rumata]

I think the instructions for Sight Reductions needs to have something like the following:

*  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.

Greetings, Wannathermal.

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.

[wannathermal]

I think the instructions for Sight Reductions needs to have something like the following:

*  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.

Greetings, Wannathermal.

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.

[Rumata]

I think the instructions for Sight Reductions needs to have something like the following:

*  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.

Greetings, Wannathermal.

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.

I'll try to reduce your example data later-need to go now-but below is my approach ( not my, but what I'm using) in dealing with it

Greetings, just as an example (My exercise)
 
Latest fix:
Lat. 39deg.35’N, Long. 001 deg. 05’ E
--------------------------------------------------------
DR (one hour later):
Lat. 39deg 39’ N, Long. 001deg14’ E
-------------------------------------------------------------
To use Pub. 249
LHA aries  = GHA arries +Long. Assumed.;
GHA aries=164deg. 33.9’
To make LHA aries even, I consider Long. Assumed 001deg. 26.1’.
Then,
LHAaries=164deg.33.9 +001deg.26.1 = 166 deg.
For Jupiter, time of observation GMT=19-23-08, Hsextant=45 deg.00.8
From NA GHAjupiter=331deg. 07.2
Using v and time corrections, GHA Jupiter= 336-55.2
------------------------------------------------------------------------------------------
LHA Jupiter= GHA +Long. Assumed.
To make LHA Jupiter even,
I consider Long. Assumed 1-04.8.  Therefore, LHA Jupiter = 336-55.2 +1-04.8 = 338-00
 
So, AP has the following coordinates, Lat.39deg.N, Long= 1-04.8E.
 
After it, using standard procedure , I find intercept and azimuth.
 
Thank you

Greetings, just as an example:
 
Latest fix:
Lat. 39deg.35’N, Long. 001 deg. 05’ E
--------------------------------------------------------
DR (one hour later):
Lat. 39deg 39’ N, Long. 001deg14’ E
-------------------------------------------------------------
To use Pub. 249
LHA aries  = GHA arries +Long. Assumed.;
GHA aries=164deg. 33.9’
To make LHA aries even, I consider Long. Assumed 001deg. 26.1’.
Then,
LHAaries=164deg.33.9 +001deg.26.1 = 166 deg.
For Jupiter, time of observation GMT=19-23-08, Hsextant=45 deg.00.8
From NA GHAjupiter=331deg. 07.2
Using v and time corrections, GHA Jupiter= 336-55.2
------------------------------------------------------------------------------------------
LHA Jupiter= GHA +Long. Assumed.
To make LHA Jupiter even,
I consider Long. Assumed 1-04.8.  Therefore, LHA Jupiter = 336-55.2 +1-04.8 = 338-00
 
So, AP has the following coordinates, Lat.39deg.N, Long= 1-04.8E.
 
After it, using standard procedure , I find intercept and azimuth.
 
Thank you

[Rdutton]

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'


Bob,

Do you mean 11° 21'  or 10° 21'   ?


This is a very curious problem though it's probably easy once you understand it.

Please tell me if the following figures are correct

Sight at- 12:18:50 
GHA= 1° 12.8'
Ap longitude= E 015° 47.2'

Sight at- 13:40:00
GHA= 21° 30.4'
Ap longitude= E 015° 29.6'

Sight at- 15:32:00 
GHA= 49° 30.8'
Ap longitude= E 015° 29.5'

If these figures are right then I'll proceed with the LOP plots.

Thanks,

Roland

[wannathermal]

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'


Bob,

Do you mean 11° 21'  or 10° 21'   ?


This is a very curious problem though it's probably easy once you understand it.

Please tell me if the following figures are correct

Sight at- 12:18:50 
GHA= 1° 12.8'
Ap longitude= E 015° 47.2'

Sight at- 13:40:00
GHA= 21° 30.4'
Ap longitude= E 015° 29.6'

Sight at- 15:32:00 
GHA= 49° 30.8'
Ap longitude= E 015° 29.5'

If these figures are right then I'll proceed with the LOP plots.

Thanks,

Roland

Roland

You are correct, and it is supposed to be...
11° 21'

Bob

[Rdutton]

Bob,

Also, are the Ap. longitude figures correct that I provided?

Thank you,

Roland

[wannathermal]

Bob,

Also, are the Ap. longitude figures correct that I provided?

Thank you,

Roland

Sorry, yes.

[Rumata]

Bob,

Also, are the Ap. longitude figures correct that I provided?

Thank you,

Roland

Sorry, yes.

I'm confused.  I started to plot assuming long. are DR not Assumed position. As I showed in my example above, I uised AP longitude to make LHA even to make it easier to use Pub.229. And so far it works in Bob's example. But if Long in Bob's example are AP so how you can plot DR position using DR latitude and AP longitude? Again, I thought both values are for DR

[Rdutton]

Bob,

I did the sun sight reduction and plotted the Lines of Position.  See the attached reduction sheet and plot. Sorry about the poor quality.

I used HO-249 Latitude 38°.  Something tells me I might be wrong but the figures I get always come out the same.

Ignore the MPP that was written on the sheets.  You were sailing so those figures are wrong.

How do my figures and plots agree with yours?

Thanks,

Roland

[Rumata]

I think the instructions for Sight Reductions needs to have something like the following:

*  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.

Greetings, Wannathermal.

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.

Bob, sorry for the delay.  My calcs. results

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 ;>

[Rdutton]

Like Rumata did so neatly, I should've written out the reduction clearly. I used Ho-249.  Here's the readable reduction;

Sight 1
2/17/2018
GMT 12:18:50

GHA- 1° 12.8'

LHA- 017°

Declination -11° 54.0'

Hc- 37° 38'

Ap λ- E 015° 47'
Zn- 202°
Intercept- 02 away


Sight 2
2/17/2018
GMT 13:40:00

GHA- 21° 30.3'

LHA- 037°

Declination -11° 53.2'

Hc- 29° 17'

Ap λ- E 015° 30'
Zn- 223°
Intercept- 09 toward


Sight 3
2/17/2018
GMT 15:32:00

GHA- 49° 30.4'

LHA- 065°

Declination -11° 51.4'

Hc- 11° 30'

Ap λ- E 015° 30'
Zn- 245°
Intercept- 09 away

[wannathermal]

You have both earned gold star stickers! These are the answers I got when I took the sights and reduced them. When I did the RF's the position was within 2 miles of where the boat was. I am always afraid I will have to re-calibrate the GPS plotter after I reduce sights.
Let's go sailing and practice checking the accuracy of the GPS's!

[Rdutton]

Now that's just great! I had failed to consider the DR positions when I plotted the LOPs.

Bob, this has been a very helpful lesson on your part. Thank you for the effort.

Now....finally...I can complete a sight reduction no matter which hemisphere I'm in.

Roland

[Rumata]

You have both earned gold star stickers! These are the answers I got when I took the sights and reduced them. When I did the RF's the position was within 2 miles of where the boat was. I am always afraid I will have to re-calibrate the GPS plotter after I reduce sights.
Let's go sailing and practice checking the accuracy of the GPS's!

Thank you, Wannathermal.