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    Re: Avoiding Wx Problem
    From: Carl Herzog
    Date: 2000 Dec 15, 11:40 AM

    Sailing a a course perpendicular to the course of the storm will NOT
    achieve the
    maximum possible CPA unless the storm is traveling at the same speed as
    you.
    This type of storm avoidance question is a relative motion plot, easily
    accomplished on a maneuvering board or a plotting sheet. However, it can
    also be
    done on a chart.
    
    -- Plot your vessel (at the center if using a maneuvering board).
    -- Plot the position of the storm center.
    -- Plot the storm�s speed vector (a line representing its direction and
    speed. In
    your second example, 265T for 22 miles). This line is drawn beginning
    from your
    current location.
    
    -- From the outer end of that line, draw a line tangent to the 12 knot
    speed circle
    (a circle with a radius of 12 nm with its center at your location).
    
    -- From your position, draw draw a perpendicular to this tangent line.
    This is the
    direction you need to travel to achieve maximum CPA.
    
    -- Extend that line in the opposite direction, until it crosses the
    course of the
    hurricane. That point represents the location of the hurricane (assuming
    course
    and speed remain the same) at the time of CPA. From there, calculate how
    long it
    will take the storm to reach that point, and you can establish the time
    'til
    CPA.
    
    --
    Carl Herzog
    Editor, Reed's Nautical Almanacs
    
    www.reedsalmanac.com
    carlzog{at}reedsalmanac.com
    -------------------------------------------
    120 Fulton Street
    Boston, MA 02109
    Ph# (617) 227-1300
    Fax# (617) 268-5905
    

       
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