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Subject: Re: Silicon Sea: Leg 73
From: Michael Wescott (wescott_mike@XXX.XXX)
Date: Fri Jun 08 2001 - 01:04:58 EDT
> 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
> @XXX.XXX7 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 @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
--
Mike Wescott
Wescott_Mike@XXX.XXX
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