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Subject: Re: Mercator vs. Great Circle Charts and Bowditch
From: Aubrey O'Callaghan (ocallaghan@XXX.XXX)
Date: Thu Aug 30 2001 - 11:34:08 EDT
It would have been nice if the first reply to Carolyn's email had directed
her to the appropriate parts of Bowditch, which as we all know, is
available on-line. Navigation can be very daunting when starting from
ground zero, more especially if ones expertise does not revolve around
mathematics. I was somewhat surprised that Bowditch was not already
mentioned as course reading material from the start.
One would expect that navigation will only be a very small part of an
Oceanography class. I'm not sure what the syllabus might be, but Carolyn,
you may find that many sections of Bowditch will be useful extra course
reading for you. Particularly the following chapters:
24: The Sailings - this is probably what will answer your initial questions
30: Hydrography and Hydrographic Reports
31: The Oceans - the first subsection of this chapter is titled "The
importance of Oceanography"
32: Ocean Currents
34: Perhaps Ice in The Sea
36: Tropical Cyclones
35: Weather Elements
37: Weather Observations
Keep in touch with us, if you have more questions, don't hesitate to post -
we will do our best to point you in the right direction.
Good luck with your course.
Aubrey.
At 03:15 29/08/01, you wrote:
>Hello, everyone!
>
>I just joined the Navigation mailing list. This semester I am taking an
>oceanography class, and this list looked interesting and informative. I am a
>novice in this area (but eager to learn!), so I am hoping to learn a lot on
>this list from the experts.
>
>We are currently studying Mercator and great circle charts, and I've already
>run into a few questions I am hoping you can help me with:
>
>1. Can true direction be determined in the same manner for all locations on a
>Mercator chart? How about on a great circle chart?
>
>2. How is the compass rose used on each of these charts?
>
>3. If I were to draw a straight line between two points (say Tokyo and Cabo
>San Lucas) on both a Mercator chart and a great circle chart, would either
>straight line represent a great circle?
>
>4. Given the straight line drawn between Tokyo and Cabo San Lucas (see
>above), which chart, the Mercator or the great circle, would give me the
>shortest route between these two points?
>
>5. Would sailing a great circle course always be the best way to travel
>across the ocean, or would ships have to take into consideration unfavorable
>winds, currents, or storms that might cause a delay?
>
>6. Do most large ships today use computer assistance to help them choose the
>best course across the ocean?
>
>I realize that these questions are very basic, but I am hoping you will share
>your expertise with a beginner. Thanks so much!
>
>Carolyn Seefer
>Diablo Valley College
>Pleasant Hill, California
=================================================================
Aubrey O'Callaghan
Wandrin' Star of Dart
Rival 38
Contact: Venezuela,
Puerto La Cruz
00-58-14-8205350 (Cellular)
00-58-281 2818 667
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