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    Re: Great Circle Course via calculator & HO 208
    From: Stan K
    Date: 2016 Oct 1, 14:24 -0400

    In addition to Peter's spreadsheets, you might find The Sailings tool of Celestial Tools helpful.  It does great circle several rhumb line calculations.  For your convenience, the latest beta is attached.  Just unzip it and run the executable.  No installation is required.  However, if you are using Norton 360 or some other Norton variations, you might get a false positive for a virus.  If this happens, you can put Celestial Tools on your personal white list within Norton.


    -----Original Message-----
    From: Peter Hakel <NoReply_PeterHakel@fer3.com>
    To: slk1000 <slk1000@aol.com>
    Sent: Sat, Oct 1, 2016 2:00 pm
    Subject: [NavList] Re: Great Circle Course via calculator & HO 208


    You mentioned a hand calculator; freely downloadable spreadsheets, sailings.xls and waypoints.xls, described in


    should be useful, if you want to experiment with these types of calculations.

    Peter Hakel

    From: Bruce J. Pennino <NoReply_Pennino@fer3.com>
    To: pmh099---.com
    Sent: Saturday, October 1, 2016 9:23 AM
    Subject: [NavList] Great Circle Course via calculator & HO 208

    A friend recently gave me Dutton's, 13 edition.  As I was flipping through the pages I noticed the section on great circle courses, calculating waypoints etc. I've done some surveying and staked out many circular curves/courses using a theodolite. So the math was interesting.  Surveyors basically use  deflection angles from a back tangent and chord distances to locate points (waypoints) along the arc.  A surveyor moves up on the curve(course) and then can layout points ahead using subdeflection angles. Of course there is no concern with curvature and non-parallel meridians. 
    Anyway using HO 208 for initial course and distance, and using Dutton's mid latitude calculation methods with a hand calculator, I tried to do a great circle course from Charleston, SC to the Lizard Point, UK.  With only 4 intervals (5 waypoints), my results did not agree very well with an online calculator. With 6 waypoints, results were somewhat better. But the course was too far north.  The rhumb line distance and course is only 3-4 % longer more than great circle.  My first question: What is the best method/equations  for locating waypoints when the initial course and great circle distance is known? I assume latitude change = distance * cosinecourse, but longitude change?
    Second question: How many waypoints would I practically need to establish a proposed  course from Charleston, SC to Lizard Point? Based on the online calculators, 6 or 7 waypoints are sufficient?  I would update my course with actual CN positioning and using HO 208 . I assume no onboard computer, GPS, etc.  I imagine back in the sailing and steamship days navigators using previous courses  and just repeated their previous successful crossings. Interesting.
    Thanks and best regards,

    File: 136737.celestialtools520.zip
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