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    Re: sextant without paper charts
    From: Robert Eno
    Date: 2008 Nov 9, 16:02 -0500

    G'day Bruce,
    
    > When you used bubble sextants on the water did you use the averaging
    > mechanism?
    
    No. They are not worth the effort. The averaging mechanism was designed for
    the relatively predictable motions of an aircraft; not the pitching, yawing,
    bouncing of a small vessel.
    
    
    The least motion I have ever seen in a vessel is flat calm
    > with 35 thousand tons of iron ore in the holds with a ship with a flat
    > bottom. You could almost shoot pool if you had a table.There was some
    > motion, but certainly less than you would find in an aircraft.
    >
    I have heard that you can balance a dime off the taffrail of a supertanker
    but the vessels I have attempted bubble sextant observations from were small
    and certainly not as stable as a 35,000 tonner! Actually, I would love to
    have an opportunity to attempt this one day, to see what it is like. But
    even at that, I have been sitting in my own boat in flat calm water with
    nary a discernable motion and the bubble still tended to be skittish.
    
    > I like your comet about the celestial navigation in the far north, as my
    > father was a bush pilot in Northern Quebec in the 60's. Magnetic compass
    > was questionable. It was all floats so you never even got to set the
    > gyro to a handy airstrip direction.There was no VOR, and few radio
    > stations to pick up on the RDF.  On top of that the land is featureless
    > and the ceiling is always low. His joke was if he took the Beaver up
    > over 1000 feet he would get a nosebleed since he was so unused to it.  I
    > gather the GPS has made things better, but it too suffers in high
    > latitudes, although I can find no published facts on this on the web. He
    > didn't have an astro-compass on his plane.
    > I have a friend who often finds himself in the North as a ship's
    > navigator who says the GPS has problems because the satellites get too
    > close to the horizon. Even the the Gyros (both mechanical and FOG) get
    > wonky too. Fortunately, the sun is always up when he is there.
    >
    
    GPS is immensely popular in these parts. Most hunters now have them strapped
    to their skidoos. I have used GPS up in Resolute Bay and Ellesmere Island
    without any apparent ill effect. That being said, I cannot say that my use
    of GPS in these parts has been extensive so I can only comment on my
    experiences during my brief interludes up there. In the southern and
    mid-Arctic; that is at Latitudes of 60 - 70 degrees, I have found GPS to be
    very reliable. Satellite phones are another matter altogether...
    
    I have a couple of astro compasses in my collection. At one time, they were
    mandatory on all aircraft flying up here but I am not certain if this is
    still the case. Regardless, I seriously doubt if most of these young pilots
    would know the difference between Venus and a streetlamp. It is, from what I
    have observed, all about button-pushing.
    
    Incidentally, do you have a copy of Kieth Greenaway's "Arctic Air
    Navigation"?  If not, you should pick up a copy. Published in 1952, it was
    at the time, on the leading edge of air navigation in the polar regions. It
    was all astro compass and sextants back then.
    
    
    Robert
    
    
    
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