NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Exercise #7 LOP's
From: Greg R_
Date: 2008 May 31, 23:58 -0700
LOP’s
A couple of straight old LOP’s for people to play with.
1) PM sunline: At UTC 06h 23m 23s on 29 May 2008, a lower limb
observation of the sun was made. DR Lat is 14deg 38.0’ N and Long is
145deg 27.6’E. Height of eye was 106’, IE is 0.0, T/P is 88 F and
1011mb. Hs is 31deg 00.6’.
2) At UTC 19h 22m 31s on 28 May 2008, a LOP of Jupiter was shot. DR
Lat is 14deg 55.9’N, Long 145deg 07.5’ E. Height of eye is 106’, IE
is 0.0, T/P is 84 F and 1010 mb. Hs is 43deg 52.4’.
Determine Azimuth and intercept.
Please tell us if you are using an assumed position, or are giving
data based off of the DR position.
Jeremy
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From: Greg R_
Date: 2008 May 31, 23:58 -0700
First off, thanks for the practice in working
sights using East longitude - it had been long enough that I'd forgotten that
for that case you subtract AP longitude minutes from 60, then add that to GHA to
get an even value of LHA. My first attempts were ending up with really long
intercepts and I couldn't figure out why until I ran it through the Navigator
software and the light bulb came on (sometimes we forget how "easy' we have it
here in the West longitudes with just subtracting to get LHA).
:-)
So, here's what I get for sight reductions using
Nautical Almanac and Pub. 249 (and Navigator agrees with me within a few tenths
of decimal points):
---------------------------
1) PM Sun line
AP Lat: 15 deg N
GHA: 276 deg 29.7'
AP Long: 145 deg 30.3'
LHA: 62 deg
Dec: N 21 deg 41.1
Hc: 31 deg 08'
Ho: 31 deg 04.4'
Intercept: 3.6 NM Away
Zn: 286 deg
---------------------------
2) Early-morning Jupiter sight
AP Lat: 15 deg N
GHA: 243 deg 46.5'
AP Long: 145 deg 13.5'
LHA: 29 deg
Dec: S 21 deg 46.0
Hc: 43 deg 31'
Ho: 43 deg 41.4'
Intercept: 10.4 NM Towards
Zn: 219 deg
---------------------------
I'm assuming this is supposed to be worked as
a running fix - and the vessel appears to have moved 27.5 NM on TC 133 deg
between fixes (which is right at 11 hours and gives an average speed of 2.5 Kts.
- are we just drifting with the current, or was there not much wind that day?).
With the LOPs plotted out it looked easier to
retire LOP #1 to the DR #2 position rather than the other way around (the
Jupiter LOP almost paralleled the vessel's course, and I figured a better "cut"
would be had that way).
So if I plotted this right (and it's been a good
long while since I plotted fixes manually), I show a position of 14 deg 50' N /
145 deg 09.8' E at 19h 22m 31s on 28 May 2008. Please tell me I'm at least in
the ballpark... ;-)
--
GregR
P.S. Navigator's solution is 14 deg 53.4' N / 145
deg 05.1' E, and I'm guessing that's a lot more accurate than my manual plotting
work.
----- Original Message -----
From: "Anabasis" <jcaoy@yahoo.com>
To: "NavList" <NavList@fer3.com>
Sent: Saturday, May 31, 2008 1:59 AM
Subject: [NavList 5224] Exercise #7
LOP's
LOP’s
A couple of straight old LOP’s for people to play with.
1) PM sunline: At UTC 06h 23m 23s on 29 May 2008, a lower limb
observation of the sun was made. DR Lat is 14deg 38.0’ N and Long is
145deg 27.6’E. Height of eye was 106’, IE is 0.0, T/P is 88 F and
1011mb. Hs is 31deg 00.6’.
2) At UTC 19h 22m 31s on 28 May 2008, a LOP of Jupiter was shot. DR
Lat is 14deg 55.9’N, Long 145deg 07.5’ E. Height of eye is 106’, IE
is 0.0, T/P is 84 F and 1010 mb. Hs is 43deg 52.4’.
Determine Azimuth and intercept.
Please tell us if you are using an assumed position, or are giving
data based off of the DR position.
Jeremy
Navigation List archive: www.fer3.com/arc
To post, email NavList@fer3.com
To , email NavList-@fer3.com
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