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    Re: Silicon Sea: Leg 73
    From: Dan Hogan
    Date: 2001 Jun 08, 7:19 AM

    On 8 Jun 2001, at 1:04, Michael Wescott wrote:
    
    > > 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 {at}
    > > 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
    
    OK.
    
    > 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
    
    OK
    
    > > 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
    Your calculations are correct. But the idiot that created the problem gave
    the wrong Hs...I changed it and forgot to correct the question.
    
    Try Hs Sun LL: 81d 19.8'.
    
    > > 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 {at} 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
    
    OK. Distance is off due to my error on Noon Lat Hs.
    >
    > --
    >         Mike Wescott
    >         Wescott_Mike{at}EMC.COM
    
    
    
    Dan Hogan WA6PBY
    C27 "Gacha"
    dhhogan{at}verimail.com
    Nav-L Page: http://www.wa6pby.com
    

       
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