Interpolation in Pub.229

[Rumata]

Gentlemen,

In a pretty routine calculation I faced a problem which forced me to redo that calc three times. Let me explain myself:

Three sighting of Sun and three sightings of Moon. Regular fix. Supposed to be.  Except one nuance: The lat is a whole number  of degrees and 30 minutes. No problem.  The question is what App.Lat. to select: 30 minutes less or 30 minutes greater to get a whole number for the entry into Pub.229. Getting suspicious results in both attempts I decided to interpolate data for Hc and Z between two neighboring Lats. Then the fix appeared to make sense.

I checked the difference between Hc  in adjoining columns.  The delta is APPROXIMATELY the same.

The bottom line: I just like to share this small occurence.  Am sure that most of you are familiar with this issue and have no problems.  But anyway, decided to share it.

By the way,  I understand that there is no direct proportionality between data in Pub.229, because all of it are solutions of navigational triangle using spherical trigs.

Thank you

[pabrides]

Gentlemen,

In a pretty routine calculation I faced a problem which forced me to redo that calc three times. Let me explain myself:

Three sighting of Sun and three sightings of Moon. Regular fix. Supposed to be.  Except one nuance: The lat is a whole number  of degrees and 30 minutes. No problem.  The question is what App.Lat. to select: 30 minutes less or 30 minutes greater to get a whole number for the entry into Pub.229.  

Thank you

It makes no difference, really, as far as I can tell. LOP is LOP and you need two or more to get a fix.  With a body observation to the south I would probably choose 30 minutes greater.  I try to make my AP such that ZN lays closest to my DR.  In other words I always try to place my AP such that my DR is between the body and the AP choice and as close as I can get it.  Where Im at (East Longitude) with a morning shot I try to use a smaller AP Long; with an afternoon shot I try to use a larger AP long. Another way to see it is that I almost always try to make HC less than HO when that ZN favors the DR.... if that makes any sense for you... :) However, it doesnt always work out that way.

Just estimating the body's azimuth (ZN) at the time of observation can make AP choices a bit easier. On the work sheet, lay a pencil down in the sun's general direction from the DR and you can easily judge which AP ZN choice will lay closest to your DR. If estimating the sun's azimuth is too difficult, as is sometimes the case, then take a compass reading of your shadow and take the reciprocal after adjusting for variation.

joe

[Rumata]

Gentlemen,

In a pretty routine calculation I faced a problem which forced me to redo that calc three times. Let me explain myself:

Three sighting of Sun and three sightings of Moon. Regular fix. Supposed to be.  Except one nuance: The lat is a whole number  of degrees and 30 minutes. No problem.  The question is what App.Lat. to select: 30 minutes less or 30 minutes greater to get a whole number for the entry into Pub.229.  

Thank you

It makes no difference, really, as far as I can tell.  LOP is LOP and you need two or more to get a fix.  With a body observation to the south I would probably choose 30 minutes greater.  I try to make my AP such that ZN lays closest to my DR.  In other words I always try to place my AP such that my DR is between the body and the AP choice and as close as I can get it.  Where Im at (East Longitude) with a morning shot I try to use a smaller AP Long; with an afternoon shot I try to use a larger AP long. Another way to see it is that I almost always try to make HC less than HO when that ZN favors the DR.... if that makes any sense for you... :)  However, it doesnt always work out that way.

Just estimating the body's azimuth (ZN) at the time of observation can make AP choices a bit easier.  On the work sheet, lay a pencil down in the sun's general direction from the DR and you can easily judge which AP ZN choice will lay closest to your DR.  If estimating the sun's azimuth is too difficult, as is sometimes the case, then take a compass reading of your shadow and take the reciprocal after adjusting for variation.

joe

---

Joe, thank you. But as you know, taking Ap too liberally will eventually make d ( Hc-Hs) too big for a reasonable LOP (because Pub.229 requires Lat. input) It was exactly what has happened in my case. Your explanation makes sense. Always taking Ap as close to your DR Lat. as possible. But when it, DR Lat., is something like N39-30, then I think interpolation is needed for Hc, and Z corresponding to 39-30, but not to 39-00 or 40-00. It was what I got.

When I tried ( in different case) change Assumed Lat for calculating LHA for a less difference with DR Lat, ( let' s say GHA is 324-07.1. And DR Lat is let's say 05-05.6E. Then the Lat. assumed is 5-52.9, to get whole number LHA. Then the difference between Dr Lat and Assumed Lat. is hell too big.) results were not always satisfactory.

Anyway, you made the point.

[pabrides]

Gentlemen,

In a pretty routine calculation I faced a problem which forced me to redo that calc three times. Let me explain myself:

Three sighting of Sun and three sightings of Moon. Regular fix. Supposed to be.  Except one nuance: The lat is a whole number  of degrees and 30 minutes. No problem.  The question is what App.Lat. to select: 30 minutes less or 30 minutes greater to get a whole number for the entry into Pub.229.  

Thank you

It makes no difference, really, as far as I can tell.  LOP is LOP and you need two or more to get a fix.  With a body observation to the south I would probably choose 30 minutes greater.  I try to make my AP such that ZN lays closest to my DR.  In other words I always try to place my AP such that my DR is between the body and the AP choice and as close as I can get it.  Where Im at (East Longitude) with a morning shot I try to use a smaller AP Long; with an afternoon shot I try to use a larger AP long. Another way to see it is that I almost always try to make HC less than HO when that ZN favors the DR.... if that makes any sense for you... :)  However, it doesnt always work out that way.

Just estimating the body's azimuth (ZN) at the time of observation can make AP choices a bit easier.  On the work sheet, lay a pencil down in the sun's general direction from the DR and you can easily judge which AP ZN choice will lay closest to your DR.  If estimating the sun's azimuth is too difficult, as is sometimes the case, then take a compass reading of your shadow and take the reciprocal after adjusting for variation.

joe

---

Joe, thank you. But as you know, taking Ap too liberally will eventually make  d ( Hc-Hs) too big for a reasonable LOP (because Pub.229 requires Lat. input)  It was exactly what has happened in my case. Your explanation makes sense. Always taking Ap as close to your DR Lat.  as possible. But when it, DR Lat., is something like N39-30, then I think interpolation is needed for Hc, and Z  corresponding to 39-30, but not to 39-00 or 40-00. It was what I got.

When I tried  ( in different case) change Assumed Lat for calculating LHA for a less difference with DR Lat, ( let' s say GHA is 324-07.1. And DR Lat is let's say 05-05.6E.  Then the Lat. assumed is 5-52.9, to get whole number LHA.  Then the difference between Dr Lat and Assumed Lat. is hell too big.) results were not always satisfactory.

Anyway, you made the point.

Let me clarify one thing...  I didnt mean to imply that AP should be as close to the DR as possible - I meant to say that I like to choose an AP whose ZN lays as close to DR as possible..  One thing is not the other.

In your example you said the assumed lat is 5-52.9.  This is wrong because your assumed lat should be a whole number closest to DR - in your case you mean Longitude i think...  Anyway you can choose AP Long 4-52.9 instead to get you closer to DR if THAT ZN also comes closer to DR. It appears in your example that you are talking about a late morning shot.... I would use the closest lat whole number north and the 4-52.9 for AP Long; this would put the DR between the AP and the body. (Im not sure what your Lat is) Then your LHA would be 329. Im thinking that unless your DR is near DEC your ZN will be something like 160 or 170.

Dont be afraid of big intercept numbers. I recently had an intercept of 52.? that put me and the ZN within a mile or two of my exact Position using a Gunter quadrant variant.

good luck
joe

[Rumata]

Gentlemen,

In a pretty routine calculation I faced a problem which forced me to redo that calc three times. Let me explain myself:

Three sighting of Sun and three sightings of Moon. Regular fix. Supposed to be.  Except one nuance: The lat is a whole number  of degrees and 30 minutes. No problem.  The question is what App.Lat. to select: 30 minutes less or 30 minutes greater to get a whole number for the entry into Pub.229.  

Thank you

It makes no difference, really, as far as I can tell.  LOP is LOP and you need two or more to get a fix.  With a body observation to the south I would probably choose 30 minutes greater.  I try to make my AP such that ZN lays closest to my DR.  In other words I always try to place my AP such that my DR is between the body and the AP choice and as close as I can get it.  Where Im at (East Longitude) with a morning shot I try to use a smaller AP Long; with an afternoon shot I try to use a larger AP long. Another way to see it is that I almost always try to make HC less than HO when that ZN favors the DR.... if that makes any sense for you... :)  However, it doesnt always work out that way.

Just estimating the body's azimuth (ZN) at the time of observation can make AP choices a bit easier.  On the work sheet, lay a pencil down in the sun's general direction from the DR and you can easily judge which AP ZN choice will lay closest to your DR.  If estimating the sun's azimuth is too difficult, as is sometimes the case, then take a compass reading of your shadow and take the reciprocal after adjusting for variation.

joe

---

Joe, thank you. But as you know, taking Ap too liberally will eventually make  d ( Hc-Hs) too big for a reasonable LOP (because Pub.229 requires Lat. input)  It was exactly what has happened in my case. Your explanation makes sense. Always taking Ap as close to your DR Lat.  as possible. But when it, DR Lat., is something like N39-30, then I think interpolation is needed for Hc, and Z  corresponding to 39-30, but not to 39-00 or 40-00. It was what I got.

When I tried  ( in different case) change Assumed Lat for calculating LHA for a less difference with DR Lat, ( let' s say GHA is 324-07.1. And DR Lat is let's say 05-05.6E.  Then the Lat. assumed is 5-52.9, to get whole number LHA.  Then the difference between Dr Lat and Assumed Lat. is hell too big.) results were not always satisfactory.

Anyway, you made the point.

Let me clarify one thing...  I didnt mean to imply that AP should be as close to the DR as possible - I meant to say that I like to choose an AP whose ZN lays as close to DR as possible..  One thing is not the other.

In your example you said the assumed lat is 5-52.9.  This is wrong because your assumed lat should be a whole number closest to DR - in your case you mean Longitude i think...  Anyway you can choose AP Long 4-52.9 instead to get you closer to DR if THAT ZN also comes closer to DR.  It appears in your example that you are talking about a late morning shot.... I would use the closest lat whole number north and the 4-52.9 for AP Long; this would put the DR between the AP and the body. (Im not sure what your Lat is)  Then your LHA would be 329.  Im thinking that unless your DR is near DEC your ZN will be something like 160 or 170.

Dont be afraid of big intercept numbers.  I recently had an intercept of 52.? that put me and the ZN within a mile or two of my exact Position using a Gunter quadrant variant.

good luck
joe

Joe, I think I didn't express myself clear enough. In my previous posts by a typo I put Lat, where it should be Long. Yes, you are right, for the assumed Lat. one needs to take the whole number. Any Publications requires the whole number for Lat. But, when you calculate LHA, which is in my case  LHA=GHA+Long., ( long.. is E and I need to get LHA as a whole number. So, when I tried to use 4 deg Long. instead of 5 deg. I got LOP so far away from two other Sun shots, one can't reach it with a  six feet pole. And, also, you're right, that I kinda afraid of big intercepts. When I got an intercept close to almost one degree-I think I did wrong.

Well, practice makes us sane. ;>

Thank you

[pabrides]

Gentlemen,

In a pretty routine calculation I faced a problem which forced me to redo that calc three times. Let me explain myself:

Three sighting of Sun and three sightings of Moon. Regular fix. Supposed to be.  Except one nuance: The lat is a whole number  of degrees and 30 minutes. No problem.  The question is what App.Lat. to select: 30 minutes less or 30 minutes greater to get a whole number for the entry into Pub.229.  

Thank you

It makes no difference, really, as far as I can tell.  LOP is LOP and you need two or more to get a fix.  With a body observation to the south I would probably choose 30 minutes greater.  I try to make my AP such that ZN lays closest to my DR.  In other words I always try to place my AP such that my DR is between the body and the AP choice and as close as I can get it.  Where Im at (East Longitude) with a morning shot I try to use a smaller AP Long; with an afternoon shot I try to use a larger AP long. Another way to see it is that I almost always try to make HC less than HO when that ZN favors the DR.... if that makes any sense for you... :)  However, it doesnt always work out that way.

Just estimating the body's azimuth (ZN) at the time of observation can make AP choices a bit easier.  On the work sheet, lay a pencil down in the sun's general direction from the DR and you can easily judge which AP ZN choice will lay closest to your DR.  If estimating the sun's azimuth is too difficult, as is sometimes the case, then take a compass reading of your shadow and take the reciprocal after adjusting for variation.

joe

---

Joe, thank you. But as you know, taking Ap too liberally will eventually make  d ( Hc-Hs) too big for a reasonable LOP (because Pub.229 requires Lat. input)  It was exactly what has happened in my case. Your explanation makes sense. Always taking Ap as close to your DR Lat.  as possible. But when it, DR Lat., is something like N39-30, then I think interpolation is needed for Hc, and Z  corresponding to 39-30, but not to 39-00 or 40-00. It was what I got.

When I tried  ( in different case) change Assumed Lat for calculating LHA for a less difference with DR Lat, ( let' s say GHA is 324-07.1. And DR Lat is let's say 05-05.6E.  Then the Lat. assumed is 5-52.9, to get whole number LHA.  Then the difference between Dr Lat and Assumed Lat. is hell too big.) results were not always satisfactory.

Anyway, you made the point.

Let me clarify one thing...  I didnt mean to imply that AP should be as close to the DR as possible - I meant to say that I like to choose an AP whose ZN lays as close to DR as possible..  One thing is not the other.

In your example you said the assumed lat is 5-52.9.  This is wrong because your assumed lat should be a whole number closest to DR - in your case you mean Longitude i think...  Anyway you can choose AP Long 4-52.9 instead to get you closer to DR if THAT ZN also comes closer to DR.  It appears in your example that you are talking about a late morning shot.... I would use the closest lat whole number north and the 4-52.9 for AP Long; this would put the DR between the AP and the body. (Im not sure what your Lat is)  Then your LHA would be 329.  Im thinking that unless your DR is near DEC your ZN will be something like 160 or 170.

Dont be afraid of big intercept numbers.  I recently had an intercept of 52.? that put me and the ZN within a mile or two of my exact Position using a Gunter quadrant variant.

good luck
joe

Joe, I think I didn't express myself clear enough. In my previous posts by a typo I put Lat, where it should be Long. Yes, you are right, for the assumed Lat. one needs to take the whole number. Any Publications requires the whole number for Lat. But, when you calculate LHA, which is in my case  LHA=GHA+Long., ( long.. is E and I need to get LHA as a whole number. So, when I tried to use 4 deg Long. instead of 5 deg. I got LOP so far away from two other Sun shots, one can't reach it with a  six feet pole. And, also, you're right, that I kinda afraid of big intercepts. When I got an intercept close to almost one degree-I think I did wrong.

Well, practice makes us sane. ;>

Thank you

LOL... Now I am very interested in your work... I also live in E long and add AP to GHA. Please send me two or three of your observations and let me try to work them... :)  please include the body, gmt time, gmt date, DR, HS, IE, dip, and any other data you think I need.

thanks
joe

[Rumata]

It makes no difference, really, as far as I can tell.  LOP is LOP and you need two or more to get a fix.  With a body observation to the south I would probably choose 30 minutes greater.  I try to make my AP such that ZN lays closest to my DR.  In other words I always try to place my AP such that my DR is between the body and the AP choice and as close as I can get it.  Where Im at (East Longitude) with a morning shot I try to use a smaller AP Long; with an afternoon shot I try to use a larger AP long. Another way to see it is that I almost always try to make HC less than HO when that ZN favors the DR.... if that makes any sense for you... :)  However, it doesnt always work out that way.

Just estimating the body's azimuth (ZN) at the time of observation can make AP choices a bit easier.  On the work sheet, lay a pencil down in the sun's general direction from the DR and you can easily judge which AP ZN choice will lay closest to your DR.  If estimating the sun's azimuth is too difficult, as is sometimes the case, then take a compass reading of your shadow and take the reciprocal after adjusting for variation.

joe

---

Joe, thank you. But as you know, taking Ap too liberally will eventually make  d ( Hc-Hs) too big for a reasonable LOP (because Pub.229 requires Lat. input)  It was exactly what has happened in my case. Your explanation makes sense. Always taking Ap as close to your DR Lat.  as possible. But when it, DR Lat., is something like N39-30, then I think interpolation is needed for Hc, and Z  corresponding to 39-30, but not to 39-00 or 40-00. It was what I got.

When I tried  ( in different case) change Assumed Lat for calculating LHA for a less difference with DR Lat, ( let' s say GHA is 324-07.1. And DR Lat is let's say 05-05.6E.  Then the Lat. assumed is 5-52.9, to get whole number LHA.  Then the difference between Dr Lat and Assumed Lat. is hell too big.) results were not always satisfactory.

Anyway, you made the point.

Let me clarify one thing...  I didnt mean to imply that AP should be as close to the DR as possible - I meant to say that I like to choose an AP whose ZN lays as close to DR as possible..  One thing is not the other.

In your example you said the assumed lat is 5-52.9.  This is wrong because your assumed lat should be a whole number closest to DR - in your case you mean Longitude i think...  Anyway you can choose AP Long 4-52.9 instead to get you closer to DR if THAT ZN also comes closer to DR.  It appears in your example that you are talking about a late morning shot.... I would use the closest lat whole number north and the 4-52.9 for AP Long; this would put the DR between the AP and the body. (Im not sure what your Lat is)  Then your LHA would be 329.  Im thinking that unless your DR is near DEC your ZN will be something like 160 or 170.

Dont be afraid of big intercept numbers.  I recently had an intercept of 52.? that put me and the ZN within a mile or two of my exact Position using a Gunter quadrant variant.

good luck
joe

Joe, I think I didn't express myself clear enough. In my previous posts by a typo I put Lat, where it should be Long. Yes, you are right, for the assumed Lat. one needs to take the whole number. Any Publications requires the whole number for Lat. But, when you calculate LHA, which is in my case  LHA=GHA+Long., ( long.. is E and I need to get LHA as a whole number. So, when I tried to use 4 deg Long. instead of 5 deg. I got LOP so far away from two other Sun shots, one can't reach it with a  six feet pole. And, also, you're right, that I kinda afraid of big intercepts. When I got an intercept close to almost one degree-I think I did wrong.

Well, practice makes us sane. ;>

Thank you

LOL... Now I am very interested in your work... I also live in E long and add AP to GHA.  Please send me two or three of your observations and let me try to work them... :)  please include the body, gmt time, gmt date, DR, HS, IE, dip, and  any other data you think I need.

thanks
joe

Joe, thank you for your interest.

The data corresponds to the hypothetical situation 12/18/1993..I just "polish" my basic knowledge, that's it ;>

Sun GMT 13-45-23   Hs 19-16.2
Sun GMT 13-47-02   Hs 19-07.8
Sun GMT 13-48-43   Hs 18-54.7

TC 120. V=6.5kn, DR @ 12-00 GMT 40-30N, 5-05E, IC=-1.0, Height of eye=10'.

One of the Sun sight appears ( in my cals of LOP) far away from the other two. But as soon as I used the interpolated data for Hc between 40 deg. Lat and 41 deg. Lat ( Z almost the same) I got much better result.

Moon sights  were very consistent:
Moon , UL 13-50-21 Hs 34-58.5
Moon        13-51-58 35-09.2
Moon 13-53-37 35-23.3


I got a fix. But it is different from what it supposed to be. Not too much, but considering small distance traveled-appreciable ;> And because. calcs were quite routine I wonder where did I screw up.

[Rumata]

Let me clarify one thing...  I didnt mean to imply that AP should be as close to the DR as possible - I meant to say that I like to choose an AP whose ZN lays as close to DR as possible..  One thing is not the other.

In your example you said the assumed lat is 5-52.9.  This is wrong because your assumed lat should be a whole number closest to DR - in your case you mean Longitude i think...  Anyway you can choose AP Long 4-52.9 instead to get you closer to DR if THAT ZN also comes closer to DR.  It appears in your example that you are talking about a late morning shot.... I would use the closest lat whole number north and the 4-52.9 for AP Long; this would put the DR between the AP and the body. (Im not sure what your Lat is)  Then your LHA would be 329.  Im thinking that unless your DR is near DEC your ZN will be something like 160 or 170.

Dont be afraid of big intercept numbers.  I recently had an intercept of 52.? that put me and the ZN within a mile or two of my exact Position using a Gunter quadrant variant.

good luck
joe

Joe, I think I didn't express myself clear enough. In my previous posts by a typo I put Lat, where it should be Long. Yes, you are right, for the assumed Lat. one needs to take the whole number. Any Publications requires the whole number for Lat. But, when you calculate LHA, which is in my case  LHA=GHA+Long., ( long.. is E and I need to get LHA as a whole number. So, when I tried to use 4 deg Long. instead of 5 deg. I got LOP so far away from two other Sun shots, one can't reach it with a  six feet pole. And, also, you're right, that I kinda afraid of big intercepts. When I got an intercept close to almost one degree-I think I did wrong.

Well, practice makes us sane. ;>

Thank you

LOL... Now I am very interested in your work... I also live in E long and add AP to GHA.  Please send me two or three of your observations and let me try to work them... :)  please include the body, gmt time, gmt date, DR, HS, IE, dip, and  any other data you think I need.

thanks
joe

Joe, thank you for your interest.

The data corresponds to the hypothetical situation 12/18/1993..I just "polish" my basic knowledge, that's it ;>

Sun GMT 13-45-23   Hs 19-16.2
Sun GMT 13-47-02   Hs 19-07.8
Sun GMT 13-48-43   Hs 18-54.7

TC 120. V=6.5kn, DR @ 12-00 GMT 40-30N, 5-05E, IC=-1.0, Height of eye=10'.

One of the Sun sight appears ( in my cals of LOP) far away from the other two. But as soon as I used the interpolated data for Hc between 40 deg. Lat and 41 deg. Lat ( Z almost the same) I got much better result.

Moon sights  were very consistent:
Moon , UL 13-50-21  Hs 34-58.5
Moon        13-51-58   35-09.2
Moon       13-53-37   35-23.3


I got a fix.  But it is different from what it supposed to be. Not too much, but considering small distance traveled-appreciable ;>  And because. calcs were quite routine I wonder where did I screw up.

Well, I worked the first two sun shots and the first moon shot the long way; this is what I got:

Ships position at 13:50:21 GMT -  40:12.2N, 04:57.5E

This puts the DR 19 nm off; the true position is to the south-west.
I could clean this up a bit if I decrease the scale, but for fun this is close enough.  I thought I captured the numbering of meridians  in the photo but I missed...  The compass rose is centered at 40N, 06E.

Notice sun 1 and sun 2 LOPs are on top of each other - thats due to the close observations and the ship having the same true course as the LOP line.  The Moon 1 LOP then almost dissects the  sun 1 intercept.

Joe, thank you. My results were 40-10, 05-31.  Supposed to be 40-23, 05-17. But we are in the same hemisphere. Meaning, we are fine ;>

[pabrides]

Joe, I think I didn't express myself clear enough. In my previous posts by a typo I put Lat, where it should be Long. Yes, you are right, for the assumed Lat. one needs to take the whole number. Any Publications requires the whole number for Lat. But, when you calculate LHA, which is in my case  LHA=GHA+Long., ( long.. is E and I need to get LHA as a whole number. So, when I tried to use 4 deg Long. instead of 5 deg. I got LOP so far away from two other Sun shots, one can't reach it with a  six feet pole. And, also, you're right, that I kinda afraid of big intercepts. When I got an intercept close to almost one degree-I think I did wrong.

Well, practice makes us sane. ;>

Thank you

LOL... Now I am very interested in your work... I also live in E long and add AP to GHA.  Please send me two or three of your observations and let me try to work them... :)  please include the body, gmt time, gmt date, DR, HS, IE, dip, and  any other data you think I need.

thanks
joe

Joe, thank you for your interest.

The data corresponds to the hypothetical situation 12/18/1993..I just "polish" my basic knowledge, that's it ;>

Sun GMT 13-45-23   Hs 19-16.2
Sun GMT 13-47-02   Hs 19-07.8
Sun GMT 13-48-43   Hs 18-54.7

TC 120. V=6.5kn, DR @ 12-00 GMT 40-30N, 5-05E, IC=-1.0, Height of eye=10'.

One of the Sun sight appears ( in my cals of LOP) far away from the other two. But as soon as I used the interpolated data for Hc between 40 deg. Lat and 41 deg. Lat ( Z almost the same) I got much better result.

Moon sights  were very consistent:
Moon , UL 13-50-21  Hs 34-58.5
Moon        13-51-58   35-09.2
Moon       13-53-37   35-23.3


I got a fix.  But it is different from what it supposed to be. Not too much, but considering small distance traveled-appreciable ;>  And because. calcs were quite routine I wonder where did I screw up.

Well, I worked the first two sun shots and the first moon shot the long way; this is what I got:

Ships position at 13:50:21 GMT -  40:12.2N, 04:57.5E

This puts the DR 19 nm off; the true position is to the south-west.
I could clean this up a bit if I decrease the scale, but for fun this is close enough.  I thought I captured the numbering of meridians  in the photo but I missed...  The compass rose is centered at 40N, 06E.

Notice sun 1 and sun 2 LOPs are on top of each other - thats due to the close observations and the ship having the same true course as the LOP line.  The Moon 1 LOP then almost dissects the  sun 1 intercept.

Joe, thank you. My results were 40-10, 05-31.  Supposed to be 40-23, 05-17. But we are in the same hemisphere. Meaning, we are fine ;>

Well... I had to go back... i screwed the pooch with declination.  Your 1993 almanac kind of threw me..  Here in this next plot I reduced the last sun shot and the first moon shot...  I should not be too far off.  cross your fingers

joe

[pabrides]

I used sun 1 and moon 3 this time and came within 2 nm of the true position.  Here is the plot - I can add the reduction figures upon request.  ...  As you can see I improved the scale to make the reduction more accurate.  This was a sneaky little problem, but Im glad I took the time to work it out.  I learned a valuable lesson... dont take anything for granted when doing a reduction... double check everything.

joe

[Rumata]

Joe, thank you. Yes, this small problem is a little bit tricky. If you would use all the shots , then you would get kind of ambiguous fix. And I'm wondering: if I wouldn't know the right answer, I would definitely stay with my first fix. Sure, I did everything as I supposed to do. My point is: if one makes a few shots within a very short interval, does he need to make an average LOPs or what the criterion? The difference in results maybe 10-12 miles. And if he does not have any other means to verify his fix. But , I'm just wondering. Again, thanks for working that problem in a right way

[pabrides]

Joe, thank you. Yes, this small problem is a little bit tricky. If you would use all the shots , then you would get kind of ambiguous fix. And I'm wondering: if I wouldn't know the right answer, I would definitely stay with my first fix.  Sure, I did everything as I supposed to do. My point is: if one makes a few shots within a very short interval, does he need to make an average LOPs or what the criterion? The difference in results maybe 10-12 miles. And if he does not have any other means to verify his fix. But , I'm just wondering. Again, thanks for working that problem in a right way

If you notice, Rumata, at the left-lower side of the last plot sheet, I made a note of how far the boat traveled in the 8 minutes of time between the sun and moon shot - she traveled less than a mile.  Even at this scale one mile is not a big deal.  Pencil error can be greater than that.

I can only answer your question by saying that with time you will develop a sighting technique that you will learn to  ALMOST trust.  I have developed my own proforma sheet that I trust about 90%.  I like to use it but I still make mistakes.... as you just witnessed.  I also use to assign a reliability factor or confidence factor to my observations so that if the weather is up I know that my shots are not that good and I shouldnt rely heavily on them.  Have you read the story about the Edmund Fitzgerald? They had radar and RDF and visuals of a lighthouse and still hit bottom.  She sank with all crew lost.

On a big ship in uneasy weather you might see 4 or 5 seamen taking observations all at the same time, then they average their readings to increase the reliability of the data.  It would be easy to see which observation was really out of line with the others and throw that one out. Taking 3 observations at one minute intervals and averaging them out would be a good way to increase the reliability of your data; much like the technique used to find local noon. I didnt even think to average your sun and moon shots - I was more interested in reducing all the shots individually to check my proforma. I may go back to your data for another try... :)

There is a reason why Loran then GPS now dominate the navigation problem - they are more precise and reliable than sextants.  If they did not have precision we wouldnt use them.  At sea using a sextant can be fun, but I wouldnt use one to find my slip at the docks.  You dont need a sextant for coastal navigation.

Have fun
joe

[pabrides]

Sooooooo, I just finished the averaging of the sun and moon shots and plotted the same.  I came within a quarter mile of the true position.  So that was the answer... AVERAGING THE SHOTS.

Sun avg:     GMT 13:46:59,  Hs 19:06
Moon avg:     "    13:51:59    "  35:10.3
   
Thank you so much, Rumata, for the intriguing nav problem..  I hope you have been working out my CN Challenge problems... they also might have some benefit for those who dabble in actual reductions.

Stay Dry
Joe

[Rumata]

Sooooooo, I just finished the averaging of the sun and moon shots and plotted the same.  I came within a quarter mile of the true position.  So that was the answer... AVERAGING THE SHOTS.

Sun avg:     GMT 13:46:59,  Hs 19:06
Moon avg:     "    13:51:59    "  35:10.3
   
Thank you so much, Rumata, for the intriguing nav problem..  I hope you have been working out my CN Challenge problems... they also might have some benefit for those who dabble in actual reductions.

Stay Dry
Joe

Averaging shots...Interesting. Let me try it again.  I tried to average LOPs and the result was better than not doing it, but let me try to average the shots. And for the practical purposes, what do you think can be the maximum time span before shots for averaging?  5 minutes, less? Well, of course it would depend on the boat's  speed and reliabilty of the shots themselves.


Thanks, Joe. As long as I know that I learn something -the day isn't lost.

[pabrides]

Sooooooo, I just finished the averaging of the sun and moon shots and plotted the same.  I came within a quarter mile of the true position.  So that was the answer... AVERAGING THE SHOTS.

Sun avg:     GMT 13:46:59,  Hs 19:06
Moon avg:     "    13:51:59    "  35:10.3
   
Thank you so much, Rumata, for the intriguing nav problem..  I hope you have been working out my CN Challenge problems... they also might have some benefit for those who dabble in actual reductions.

Stay Dry
Joe

Averaging shots...Interesting. Let me try it again.  I tried to average LOPs and the result was better than not doing it, but let me try to average the shots. And for the practical purposes, what do you think can be the maximum time span before shots for averaging?  5 minutes, less? Well, of course it would depend on the boat's  speed and reliabilty of the shots themselves.


Thanks, Joe. As long as I know that I learn something -the day isn't lost.

Good question...  I would assume the closer the better.  There is a broad expanse of time during the day when there is a change in rate of elevation.  One obvious rate change is just before noon to just after when the sun seems to hang at or near the same elevation for a good deal of time.  Much of the mid day has rate change that would be hard to compensate for if the observations were spaced too far apart.  According to the graphs Ive seen, the more stable part of the day is early morning and late afternoon, but if you are trying to ascertain midday or noon time by equal altitude the observer is taking shots at the worst change-of-elevation-rate times.  Yep - closer is better.  One minute between shots is recommended. 

joe