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Subject: Silicon Sea II: Leg 56
From: Dan Hogan (dhhogan@XXX.XXX)
Date: Thu Jul 01 1999 - 10:33:25 EDT
Chart(s): Plotting Sheet
Sight Reduction and
Dead-Reckoning problem Leg 56 070199 Test your knowledge!
---------------------- ------ ------ --------------------
The DR position is (42d 39.8'S 98d 51.5'W) at 11:50:00UT @XXX.XXX
TC 114.1d, Speed 10.3 Kts. We are headed for Trans Ocean Point 2
(52d 30.0'S 100d 00.0'W), where we will alter course to head for
Cape Horn(56d 40.0S 67d 15.0'W). The weather is intermittent gales,
solid overcast sky with fracto-cumulus of bad weather. The South
Atlantic Ocean Pilot indicates the current Set is 090d, Drift 15 Kts
per day.
1) What is the TC and Distance to Trans Ocean Point 2(TOP2)?
-- ---------------------------------------------------------
We examine our charts and see that the nearest land lies along the 75
degree longitude line. We decide to head directly for Cape Horn
(56d 40.0S 67d 15.0'W) from our DR position(52d 39.8'S 98d 51.5'W).
2) What is the TC and Distance to Cape Horn?
-- -----------------------------------------
We are caught by a severe storm and are buffeted for two days. On the
evening of the second day the storm begins to subside. The clouds begin
to raise and thin. By 23/03/1999 there are several breaks in the cloud
cover. Var 30dE, Dev 3dW. Speed 10.3 Kts. On the TC for Cape Horn.
At 13:48:23UT @ 23/03/1999 the sky clears so that we are able to take
some sights. We use the steering compass to take bearings.
3) What is the DR position at 13:48:23UT @ 23/19/1999?
-- ---------------------------------------------------
We get the following sights:
UT Body Hs
23:48:23 Sirius 50d 42.7'
23:49:01 Rigil Kentaurus 37d 43.2'
23:49:44 Aldebaran 11d 26.4'
23:50:30 Unknown 11d 59.6' 31.4d Compass Bearing,
moderate bright
23:51:01 Atria 37d 30.5'
23:52:11 Unknown 63d 03.2' 343.8D Compass bearing,
moderate bright
4) What is the FIX position?
-- -------------------------
5) What is the total compass error?
What is the Variation?
-- --------------------------------
6) What is the TC and Dist to Cape Horn(56d 04.0'S 67d 15.0'W)
-- -------------------------------------------------------------
The Pilot Chart for The South Pacific Ocean shows that the current near
our FIX position Sets 130d, Drift 25 Kts per Day. Our Var is 3dW.
7) What is the Compass Course(CC)/Course-to-Steer for Cape Horn?
-- -------------------------------------------------------------
8) Based on all the data available from the Pilot Chart, and our Nav
Log, what is our best estimated Zone Time(ZT) arrival at Cape Horn?
-- ------------------------------------------------------------------
NOTE:
Lat & Lo = XXd XX.X', Date=DD/MM/YY, HE 9 Feet, Index correction
-2.5', Time hh:mm:ss in UT,unless otherwise stated. Silicon
Sea II is a 34,000 lb(15.40t) displacement sailing vessel, 48' 3"
(14.70m) LOA. 39' (12.00m) LWL; Cutter rigged. Can tack to 45d.
Water Tanks = 220 gal(1000 ltrs). Fuel Tanks = 155 gal(700 ltrs).
Fuel consumption .675 gal/Hr at 8.5 Kts. DR(Ded-Reckoning)=position
by sailings, EP(Estimated Position)=DR+current affect. Dist to
Horizon: Nmi = SQRT HE@XXX.XXX
PLEASE respond with your results and thinking on these exercises to
the NAVIGATION list at large. If you have questions or problems, A
lot of folks on the list are knowledgeable and willing to help. Any
questions or doubtful areas will be responded to promptly. Let us
hear from you soon!
Good Navigating!
-=The Navigation List Working Group=-
Peter Smith - PSmith@XXX.XXX
John Simmonds- mobi@XXX.XXX
Jim Manzari - manzari@XXX.XXX
Dan Hogan - dhhogan@XXX.XXX
Dan Hogan WA6PBY
dhhogan@XXX.XXX
Navigation-L: http://nav.cnchost.com
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