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    Re: Avoiding Wx Problem
    From: Aubrey O´Callaghan
    Date: 2000 Dec 16, 11:32 AM

    Carls answer is absolutely correct !
    A very good source of relative motion problems is the Admiralty Navigation
    Manual Vol. III. mine is a 1938 version.
    The equivalent to this problem is stated somewhat differently in the manual
    " Avoiding Action. A Ship of lesser speed escaping from a ship of greater
    speed (In this case it was a merchant ship escaping a sloop at dusk ).
    There are even torpedo firing problems... most useful for the recreational
    sailor !!!!
    At 01:40 PM 15-12-00 -0500, you wrote:
    >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
    >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
    >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
    >Carl Herzog
    >Editor, Reed's Nautical Almanacs
    >120 Fulton Street
    >Boston, MA 02109
    >Ph# (617) 227-1300
    >Fax# (617) 268-5905
    Aubrey O'Callaghan
    Wandrin' Star of Dart
    Rival 38
    Contact: Venezuela,
    Puerto La Cruz
    00-58-14 210 4625 (Cellular)
    00-58-81 818 667

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