NavList:
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Re: Silicon Sea : Leg 69
From: Yves Arrouye
Date: 2001 Apr 09, 18:55 EDT
From: Yves Arrouye
Date: 2001 Apr 09, 18:55 EDT
Hi, Here's my navigation. I have to thank Ed Falk for his sample leg (http://www.best.com/~falconer/Navigation/) which was a great help (the plotting sheets were nice, especially since my local West Marine didn't carry the real ones). I used as much of the online government calculators I could find, and included links to them. They're really nice. I'll do other legs using paper after I get the books :) > Chart(s): Plotting Sheet > > 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 @ > 12:30:01UT. > Our Speed has been 10.7 Kts, TC 288.9d Var 19dW. Dev 1.5dE. > Current Set > 285d > Drift 0.5Kts. Using a transverse table (http://pollux.nss.nima.mil/calc/traverse.html), we use: Course angle: 288d 54' Distance: 107 (10.7 * 10 hours, which includes an approximation for the current) and we find: Difference of latitude: 0d 34.66' Departure: 101.23 which gives us: Difference of longitude: 1d 43.1' (102.23 * cos 11) Our DR position is: 1 11 1 10d 27.9'N 52d 26.4'W + 34.7' + 1d 43.1' ---------- ---------- 11d 02.6'N 54d 09.5'W We'll use an AP of 11d 00.0'N and 54d 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? > -- ------------------------- Instead of a paper Almanac, I used the celestial navigation data from the U.S. Naval Observatory at http://aa.usno.navy.mil/ (then click on Data Service and then click on Celestial Navigation Data). This page gave me Hc and Zn directly, which I feel is cheating. Is there a page there that would give me just the almanac data? Star: 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 +/- ie: - 2.5 - 2.5 - 2.5 - 2.5 - 2.5 -dip: - 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 +/- ro: - 1.8 - 1.1 - 3.6 - 3.5 - 1.2 --------- --------- --------- --------- --------- Ho: 28 09.1 42 14.1 15 46.3 13 17.6 37 49.5 GHA: 109 29.3 9 51.2 86 01.4 130 33.5 46 01.0 Decl: - 16 43.2 - 11 9.8 - 59 30.9 6 20.8 61 45.3 --------- --------- --------- --------- --------- Hc: 28 32.3 40 51.1 14 56.3 14 21.1 38 54.8 Zn: 243.9 115.4 196.2 273.8 4.8 Int: 23.2 A Big intercepts! Wow. If I plot these, I end up near 10d 53'. Using this as a new AP, I get: Star: Sirius Spica Avior Bellatrix Dubhe --------- --------- --------- --------- --------- Hc: 28 05.1 42 10.1 15 37.1 13 18.0 37 59.6 Zn: 244.8 115.1 196.7 274.2 4.2 Int: 4.0 T 4.0 T 9.2 T 0.6 A 10.1 A Much better intercepts. The fix reads 9d 50'N 53d 00'W. > |2) What is the TC and distance to Barbados(13d 10.0'N 59d 20.0'W)? > -- ---------------------------------------------------------------- From 4mulas.txt (an attachment to http://www.i-DEADLINK-com/lists/navigation/9805/0001.html), part 1, mid-latitude sailing: Fix L1: 9 50.0'N 53 00.0'W Destination L2: 13 10.0'N 59 20.0'W -------- --------- Diff.: 3 20.0'N 6 20.0'W l = 200.0'N DLo = 380.0'W 1/2 l: 1 40.0' + L1: 9 50.0' --------- Lm: 11 30.0' 1) p = DLo * cos Lm = 380 * cos 11 30.0' = 372.37 nm 3) tan C = p / l tan C = 372.37 / 200 = 1.86 C = 61.75 = 61 45.5' Thus the course is (360 - 61 45.5') = 298 degrees. 2) DLo = p / cos Lm = 372.37 / cos 11 30.0' = 379 nm > |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 @ > 12:13:00ZT. > > 3) What is the DR position? > -- ------------------------ What is a good resource to convert from ZT to UT given one's lat/lon? > 4) What day of the week is this? > -- ----------------------------- According to my calendar, it's a Saturday..