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    Set, drift, and leeway
    From: Bill B
    Date: 2006 Jan 28, 17:19 -0500

    This initially started out as a quest to see if it mattered which order
    leeway, and set and drift were applied when calculating the new course to
    steer to make good a rhumb line course to destination.  So far, it does not
    seem to matter.
    
    The lovely part of the vector diagrams and equations in my texts is that
    they assume constant speed, or the ability to increase speed in some
    situations.
    
    It occurs to me that a sailboat is usually running at the best speed she can
    make, conditions permitting.  A change of course, assuming wind direction
    remains constant, will alter speed unless she is able to run at hull speed
    on all points of sail.
    
    This is where red flags started popping up.  Assume a wind from the north,
    0d, 10 knots.  Rhumb-line course to destination 90d.  She is on a screaming
    beam reach at 7 knots.  Leeway 6d.  Set 180d, drift 3.
    
    To make good the intended track of 90d, she will have to come up
    approximately 29d, steering a course of approx. 61d.  She would also have to
    increase speed through the water.  But by coming up towards a close reach,
    she loses speed through the water.  As she loses speed, the angle from the
    rhumb line to compensate for leeway, and set and drift, increases. As the
    angle increases she goes to yet a higher point of sail, so speed decreases
    again....and on and on.
    
    Which brings up the question, is there some slick way to solve this problem?
    
    Bill
    
    
    

       
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