04-29-2020, 01:29 PM
(This post was last modified: 04-29-2020, 03:43 PM by c_davidson.)
Ray,
I don't know whether they're using Ho-249 or Ho-229 or if they're just using a calculator. The resulting plots will all be close to each other.
Using the time diagram the specifics are as follows;
Date= January 16, 1981 (why must it always be "1981"?)
GMT= 21:09:50 (corrected for chronometer error)
Ho= 13° 42' (13° 41.9')
GHA= 134° 58'
Sun's declination= S 20° 49.4'
LHA= 298° (determined by 135° (GHA rounded up) 164° (DR Longitude rounded up)
Hc= 33° 49' (33° 48.7')
Zn= 121°
Intercept= 07' Away
Comment- The answer they provide is incorrect or they're being exceeding picky. But......
Correct answer is 06.8' Away. Round it up to 07' (seven minutes)
Why? Because they're using a LHA of 298° 49' and a DR Latitude of N 27° 09'. There's no way in the world I'd do that- I'm not that smart and my pencil width, when plotting the LOP, will negate such accuracy.
Zn= 122° 30' (Ho-249 gives a Zn of 121°)
In using the Hc and Z formulas you'll get the answer of 0° 06.8' (after comparing Ho and Hc) and the Zn of 122° 30'.
In what you and I do, no one.....no one is going to argue about 1 nm. The boat's rolling, we might be half awake, the pencil broke, the boat needs tending at the most important moment of these calculations so some error shows that we're sailors and therefore human. Once plotted there will be no difference in the LOP between their answer and mine.
Phew. I'd like to see the reasoning for the answers they provide. Could I be wrong? Of course. But my answers are close enough to theirs. My erasure is probably more worn out, though.
Ray, I hope this helps you.
Clen
I don't know whether they're using Ho-249 or Ho-229 or if they're just using a calculator. The resulting plots will all be close to each other.
Using the time diagram the specifics are as follows;
Date= January 16, 1981 (why must it always be "1981"?)
GMT= 21:09:50 (corrected for chronometer error)
Ho= 13° 42' (13° 41.9')
GHA= 134° 58'
Sun's declination= S 20° 49.4'
LHA= 298° (determined by 135° (GHA rounded up) 164° (DR Longitude rounded up)
Hc= 33° 49' (33° 48.7')
Zn= 121°
Intercept= 07' Away
Comment- The answer they provide is incorrect or they're being exceeding picky. But......
Correct answer is 06.8' Away. Round it up to 07' (seven minutes)
Why? Because they're using a LHA of 298° 49' and a DR Latitude of N 27° 09'. There's no way in the world I'd do that- I'm not that smart and my pencil width, when plotting the LOP, will negate such accuracy.
Zn= 122° 30' (Ho-249 gives a Zn of 121°)
In using the Hc and Z formulas you'll get the answer of 0° 06.8' (after comparing Ho and Hc) and the Zn of 122° 30'.
In what you and I do, no one.....no one is going to argue about 1 nm. The boat's rolling, we might be half awake, the pencil broke, the boat needs tending at the most important moment of these calculations so some error shows that we're sailors and therefore human. Once plotted there will be no difference in the LOP between their answer and mine.
Phew. I'd like to see the reasoning for the answers they provide. Could I be wrong? Of course. But my answers are close enough to theirs. My erasure is probably more worn out, though.
Ray, I hope this helps you.
Clen