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    Navigating Around Hills and Dips in the Ocean
    From: David Hoyte
    Date: 2003 Aug 13, 22:29 EDT

            The joint NASA-German GRACE project has released the most
    accurate map yet of Earth's gravity field. It shows Gravity Anomaly,
    (mGal), on a global map at the URL:

            These gravity anomalies cause the geodic heigh of the ocean's
    surface to vary around the world by up to 200 meters, 650 feet. Ref:

            In the Atlantic ocean, for example, there is a hill South of
    Greenland of +200 feet, and a dip in the Caribbean of -250 feet, approx.

            I heard as far back as 1975, at the IBM Maritime Center in
    Italy, that a large ship will use significantly more fuel if it passes
    down into a gravitational dip and climbs the other side, rather than
    following a longer path around the dip which will keep it more "on the

            Is there a published algorithm that relates the parameters
    such as ship's tonnage, the size of the hill or dip, the path followed
    and fuel savings?

            Is there perhaps a simple "rule of thumb" for the courses to
    steer, for use at sea?

    David Hoyte, MA Cantab, (DavidHoyte@aol.com)
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