# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

**Re: Silicon Sea : Leg 69**

**From:**Dan Hogan

**Date:**2001 Apr 10, 01:26 EDT

On 9 Apr 2001, at 15:55, Yves Arrouye wrote: > 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.. Dan Hogan dhhogan@XXX.XXX