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    Re: My plotting board
    From: Bill B
    Date: 2015 May 09, 19:37 -0400

    On 5/9/2015 4:21 PM, Frank Reed wrote:
    > ...but setting that aside, when you are done, what do you have? Well, you
    > have an unmarked Mercator chartlet of a small part of the world...Tell me, 
    Bill or anyone else, why do you
    > personally think you need a Mercator chart? It's not a trick question.
    > I'm just curious what you think you would get from one.
    
    For the following reasons, not necessarily in order:
    
    It seemed, like cel nav, an interesting exercise given the ease of
    performing it with Adobe Illustrator.
    
    While the chart for all of Lake Michigan is Mercator, chart 14905
    (southern end) is not. Although too small to worry about, each delivers
    a slightly different course and distance between points (or
    rectangular-to-polar computations). Not good for an OCD navigator!
    
    It's handy to have a clip-board size Mercator chart (destinations
    already laid in) for my little corners of the world, allowing me to sit
    in the cockpit and enjoy beer and skittles with the boys while tracking
    our upwind tacks or off-the-wind progress (via GPS) to Chicago, St Joe
    MI, South Haven MI or our home port.
    
    I can check DR vs. GPS to help polish DR skills and determine leeway etc.
    
    UPS may be handy for fixes transferred to a chart, but not so much
    outside that use.
    
    Similar to calculating the rhumb line course distance between Michigan
    City, IN and Chicago, or how many feet north off the rhumb line the
    great circle course takes us--IT'S FUN!
    
    > Can anyone
    > suggest an important reason for using an actual Mercator chart for
    > celestial navigation?
    
    Rhumb line courses/angles can be measured directly yielding course and
    distance directly.
    
    > And what are the disadvantages of a Mercator
    > projection (hint: Greenland)?
    
    Tedious calculations for long distance sailing requiring great circle
    routes.
    
    As per your hint, areas are not proportional so it distorts the sizes of
    land masses nearer the poles, making them appear larger.
    
    Countries further north and south of equator tend to be more prosperous
    and are populated by peoples of northern European origin, which leads
    to...(and Lord help me I don't understand why) some believing that this
    purely mathematical projection, arguably the most used projection for
    navigation, is racist.
    

       
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