NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Mercator vs. Great Circle Charts and Bowditch
From: Aubrey O´Callaghan
Date: 2001 Aug 30, 9:34 AM
From: Aubrey O´Callaghan
Date: 2001 Aug 30, 9:34 AM
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