NavList:
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Re: Silicon Sea: Leg 73
From: Michael Wescott
Date: 2001 Jun 07, 11:05 PM
From: Michael Wescott
Date: 2001 Jun 07, 11:05 PM
> We are bound for a waypoint North of Aruba called Aruba Gap(13d 50.0'N > 70d 00.0'W).Our last position FIX was (13d 30.0'N 67d 00.0'W) 01/06/2001 > @ 09:39:00UT. Speed 9.5 Kts Var 10dW Dev 1dE. Current Drift 0.7 Kts, > Set 275.0d. > > 1) What is the Compass Course/Course-to-Steer for Aruba Gap(13d 50.0'N > 70d 00.0'W)? > -- ------------------------------------------------------------------- dLat = 13d 50.0'' - 13d 30.0' = 20.0 dLo = 70d 00.0' - 67d 00.0 = 180.0' Since we're in low latitudes and going almost due west, error in choice of mid-latitude gives rise to very small error in calculations. dep = 180.0 * cos 13d 40.0' = 174.9 TC = 270 + atan 20.0/174.9 = 276.5 CC = TC + 10 - 1 = 285.5 With the current going almost exactly our way, there's no point in correcting CC for current. > At 14:30:22UT the same day. We take an Sight of the SUN LL. Hs 60d 54.0'. > Speed 9.5 Kts, TC 276.5d. > > 2) What is the DR position at the time of the 14:30:22UT sight? > -- ------------------------------------------------------------ dT = 14:30 - 09:39 = 04:51 Dist = 9.5 * 4.85 = 46.1 dLat = 46.1 * sin 6.5 = 5.2 Dep = 46.1 * cos 6.5 = 45.8 dLo = 45.8 / cos 13.5 = 47.1 DR = 13d 25.2'N 67d 47.1'W > We continue sailing and prepare for a Noon sight which according to the > Nautical Almanac occurs at 11:58:00LMT. > > 3) What is the estimated Zone Time(ZT) of our Local Meridian Passage? > Only required to the nearest whole minute. > -- ------------------------------------------------------------------- We are near the Eastern edge of the zone GMT-5, therefore LAN is going to be about 11:30 ZT or 16:30 UT or 2 more hours of sailing. At 9.5 knots this will put us just to the west of 68W or 7d E of the center of the zone. LAN should be 7/15 * 60 = 28 minutes sooner. 11:30 GMT-5 > Ten minutes before LAN we are on deck and prepare for a Noon Sight. > SUN LL Hs 81d 16.3'. > > 4) What is the Noon latitude? > -- -------------------------- Hs = 81d 16.3' Ic = -2.5 Dip = -2.9 ================= Ha = 81d 10.9' Main = +15.8' ================ Ho = 81d 26.7 Since the Sun's Declination is > Lat, Lat = Dec - 90 + Ho. Lat = 13d 34.2N > Using the morning Sun sight at 09:30:22ZT and the Noon LAN work a > RunningFIX(RFIX) to the Noon sight. > > 5) What is the Running FIX(RFIX) position? > -- --------------------------------------- Plotting a 2 hour run @ 9.5 + 0.7 = 10.2 knots gives RFIX of: 13d 34.2N 67d35.0W > Speed 9.5Kts, Var 9dW, Dev 1.0dE. Current Set 270.0d Drift 1.0Kts. > > 6) What is the Estimated Zone Time of Arrival(ETA) at Aruba Gap > (13d 50.0'N 70d 00.0'W): > ZT time and date? > UT time and date? > -- ------------------------------------------------------------ >From plotting sheet, estimated distance is about 140 nmi. SOG is 9.5 + 1.0 = 10.5 knots Time elapsed is 13h20m UTC = 16:30 + 13:20 = 29:50 = 0550 2/6/2001 ZT = 0050 2/6/2001 (GMT-5) > We will change our heading when the elapsed time and distance on the > Knotmeter log indicate that we are at the Aruba Gap(13d 50.0'N 70d 00.0'W) > waypoint. > > 7) What is the TC, Compass Course(CC)/Course-to-Steer, and distance from > the RFIX to Aruba Gap? > -- ---------------------------------------------------------------------- Again estimating from plotting sheet TC = 276.5 Dist = 140nmi CC = 276.5 + 9 - 1 = 284.5d -- Mike Wescott Wescott_Mike@EMC.COM