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    Re: Navigating Around Hills and Dips in the Ocean
    From: Dan Allen
    Date: 2003 Aug 16, 21:27 -0700

    On Friday, August 15, 2003, at 09:11 PM, David Hoyte wrote:
    
    > I feel that further theoretical discussions would be fruitless at this
    > stage.
    
    Well I feel that further clarification IS needed.
    
    Dr. Paul Finlayson after reading the first initial post by David Hoyte
    and the first reply from George Huxtable has this to say regarding
    hills and dips in the Ocean:
    
    ---
    
    George Huxtable is right.  David Hoyte is wrong.  Yes, the ocean has
    hills and dips.  But it is not any harder for a ship to go 'up' one of
    these hills than 'down'.  This is because the gravitational 'straight
    down' direction (the direction a rock would fall) is always normal to
    the water surface, even on the hills and dips.  Or, to put it another
    way, the mean ocean surface is locally always 'gravitationally level',
    so the ship's motion is never doing any work against gravity.  (Note
    that if the ocean surface were not 'gravitationally level', the water
    would simply flow downhill until local 'levelness' is achieved - which
    is basically what George Huxtable was saying.)
    
    (DISCLAIMER: this argument only considers the static gravitational
    anomaly - which I assume is the major effect causing these hills and
    dips.  There may be other (probably much smaller) things going on in
    the real rotating world that would make one ship path slightly harder
    than another.  But that's not what we are talking about here.)
    
    ---
    
    Dr. Finlayson has degrees in Physics and Mechanical Engineering and
    works at the Jet Propulsion Laboratory in Pasadena, California.  He is
    a noted authority with regards to celestial mechanics and satellites.
    He can be reached at Paul.A.Finlayson{at}jpl.nasa.gov if needed.  (He is
    not a member of this NAV-L mailing list.)
    
    
    

       
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