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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>