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Re: Silicon Sea : Leg 69
From: Michael Wescott
Date: 2001 Apr 09, 11:43 EDT
From: Michael Wescott
Date: 2001 Apr 09, 11:43 EDT
I tried sending this once before but it seems to have gotten lost ...
Well this one has me stumped. I'm either missing something, or I'm
so rusty that I'm a danger to myself and others should I get on my
boat anytime soon.
>
> Dead-Reckoning problem Leg 69 040401 Test your knowledge!
> ---------------------- ------ ------ --------------------
>
> The last DR position was(10d 27.9'N 52d 26.4'W) on 18/05/2000
> @XXX.XXX Dev
> 1.5dE. Current Set 285d Drift 0.5Kts.
Figure roughly 10hrs @XXX.XXX Using traverse tables
for 289 d we get
D.Lat = 34.8
Dep = 101.2
D.Lo ~= 101.2 / cos 11 = 103.1
10 27.9N 52 26.4W
34.8 103.1
========= =========
11 02.7N 54 09.5W
Using A.P. of 11 00.0 N and 54 00.0 W.
> On that evening we take the following sights:
>
> Body UT Hs
>
> Sirius 22:15:30 28d 16.3'
> Spica 22:17:02 42d 20.6'
> Avior 22:19:00 15d 55.3'
> Bellatrix 22:19:45 13d 26.5
> Dubhe 22:20:12 37d 56.1'
> 1) What is our FIX position?
> -- -------------------------
Using AP 11N 54W:
Sirius Spica Avior Bellatrix Dubhe
UT 22:15:30 22:17:02 22:19:00 22:19:45 22:20:12
Hs 28 16.3 42 20.6 15 55.3 13 26.5 37 56.1
IC -2.5 -2.5 -2.5 -2.5 -2.5
Dip (9') -2.9 -2.9 -2.9 -2.9 -2.9
======== ======== ======== ======== ======== ========
Ha 28 10.9 42 15.2 15 49.9 13 21.1 37 50.7
R -1.8 -1.1 -3.4 -4.0 -1.2
======= ======== ======== ======== ======== ========
Ho 28 09.1 42 14.1 15 46.5 13 17.1 37 50.7
GHA-A(:00) 206 53.2 206 53.2 206 53.2 206 53.2 206 53.2
GHA-A(inc) 3 53.1 4 16.2 4 45.8 4 57.1 5 03.8
SHA 258 43.0 158 41.8 234 22.5 278 43.3 194 04.0
Long -54 00.0 -54 00.0 -54 00.0 -54 00.0 -54 00.0
========== ======== ======== ======== ======== ========
GHA-star 415 29.3 315 51.2 392 01.5 436 33.6 352 01.0
Lat 11 00.0 11 00.0 11 00.0 11 00.0 11 00.0
Dec -16 43.2 -11 09.8 -59 30.9 6 20.8 61 45.3
Hc 28 32.3 40 51.1 14 56.3 14 21.0 38 54.8
Z 243.9 115.4 196.2 173.8 004.8
Delta(dir) 23.2 A 83.0 T 50.2 T 64.0 A 65.3 A
Plotting these gives a fix near 10 00.0 N and 53 00.0W. Reducing sights
again with A.P. of 10 N and 53 W:
GHA-star 416 29.3 316 51.2 393 01.5 437 33.6 353 01.0
Lat 10 00.0 10 00.0 10 00.0 10 00.0 10 00.0
Dec -16 43.2 -11 09.8 -59 30.9 6 20.8 61 45.3
Hc 28 05.1 42 10.1 15 37.1 13 18.0 37 59.6
Z 244.8 115.1 196.7 274.2 004.2
Delta 4.0 T 4.0 T 9.4 T 0.9 A 10.1 A
Plotting these gives a good fix at about 9d 50.5'N 53d 00.0' W
This is a bit far off course. What did I get wrong?
Every thing gets further askew from here on...
> 2) What is the TC and distance to Barbados(13d 10.0'N 59d 20.0'W)?
> -- ----------------------------------------------------------------
Hmmm ... isn't that a few miles east of Barbados?
Barbados 13 10.0 59 20.0
Fix - 9 50.5 - 53 00.0
======== ========
D.Lat = 3 19.5 D.Lo = 6 20.0
= 199.5' = 380.0'
dmp = mp(13d 10.0') - mp(9d 50.5')
= 202.3
TC = 270 + arctan(202.3/380.0)
= 270 + 28
= 298d
Dist = 199.5/sin 28
= 424.5
> We continue sailing maintaining the same speed and True Course with an
> overcast sky. Then, with the navigator on deck waiting for an opening
> for a Sun shot, we see a spot of land on the horizon ahead. It is
> 20/05/2000 @XXX.XXX
> 3) What is the DR position?
> -- ------------------------
S = 10.7 C = 288.9 T,
20/05/2000 12:13:00 ZT = 20/05/2000 16:13:00 UT
-18/05/2000 22:20:00 UT
========================
1 day 17:53:00
or 41.88 hrs
Dist = 41.88 * 10.7 = 448.1 nmi
D.Lat = 448.1 * cos 288.7 = 145.2 = 2d 25.2'
DR Lat = 9d 50.5' + 2d 25.2' = 12d 15.7'
dmp = mp(12d 15.7') - mp(9d 50.5')
= 147.0
D.Lo = 147.0 * tan(288.9)
= -429.4
= -7d 09.4
DR Lo = -53d 00.0 - 7d 09.4'
= -60d 09.4
DR 12d 15.7'N 60d 09.4'W
Actually this is too far off to make any sense.
We seem to be well past Barbados.
> 4) What day of the week is this?
> -- -----------------------------
>From the almanac -- Saturday.
This I'm (almost) sure I have right :-)
<PRE>
--
Mike Wescott
wescott@XXX.XXX
</PRE>
