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Subject: [Nml] DR
From: Millard Kirk (mkirk@XXX.XXX)
Date: Mon Feb 22 1999 - 01:06:06 EST
Silicon Sea,
On Leg 46 of the Silicon Sea cruise I made an assumption on one of the
problems and then went back and change the answer after re-reading the
question.
Well it looks as if I have done it again on Leg 47.
The use of calculator and computer makes working navigation problems easy,
but sometime we tend to forget the basic definitions.
Problem:
2) What is the DR at 1930ZT?
I must admit that these problem have been a great learning experience for
me. If one uses the current to get the DR is it really DR or estimate
position (EP). Bowditch - Dead reckoning (DR) determines position by
advancing a known position for courses and distances. A position so
determined is called a dead reckoning (DR) position. It is generally
accepted that only course and speed determine the DR position. Correcting
DR position for Leeway, current effects and steering error results in an
estimated position (EP)
Minor point - I am not getting picky in problem 2. It's just that I used
my Celesticomp V to do these problems. It started me to thinking how it
works, since I have not used it for several months I have to review and
understand the working of it.
I started with the "Plan" which gives me "Rhumb Line Dist.", "Rhumb Line
True Course" and if you plug in the VAR and DEV you get the "Magnetic Course
or Compass Course (CS)"
To get DR on the Celesticomp V it asks for Departure Lat & Lon, Steered,
Speed, Var&Dev and Turn Point time. I guess the "Steered" always did drive
me little crazy in the DR program because there is a program that is called
STEER/CUR which give one the Course to Steer if one has Desired Course (TC)
Var&Dev, Log Speed, Current Dir, and Current Velocity. So if I use the
"Steered" Compass course from the STEER/CUR in my DR program I actually get
EP not DR.
Going back an looking up what DR means has helped me straighten out the
difference between DR and EP, and my Celesticomp V. I guess one should use
all the information he has arrive at the DR-EP.
Still...............
Learning the Hard Way!!
Millard Kirk KB8YQO | mailto:mkirk@XXX.XXX
116 Lewis Ave | Homepage- http://webpages.marshall.edu/~mkirk/
Barboursville, WV | A West Virginia Blue Water Sailor
25504 | Phone: (304) 736-6544
First United Methodist Church, Barboursville, WV
Homepage http://www.gbgm-umc.org/bfumcwv/
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