NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Navigating Around Hills and Dips in the Ocean
From: Dan Allen
Date: 2003 Aug 16, 21:27 -0700
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@jpl.nasa.gov if needed. (He is not a member of this NAV-L mailing list.)