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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.
    Navigation List archive: www.fer3.com/arc
    To post, email NavList@fer3.com
    To unsubscribe, email NavList-unsubscribe@fer3.com

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