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Subject: Re: Silicon Sea: Leg 73
From: Dan Hogan (dhhogan@XXX.XXX)
Date: Fri Jun 08 2001 - 09:18:55 EDT
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 @
> > 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 @XXX.XXX2 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@XXX.XXX
Dan Hogan WA6PBY
C27 "Gacha"
dhhogan@XXX.XXX
Nav-L Page: http://www.wa6pby.com
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