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    Re: sextant without paper charts
    From: Bruce Hamilton
    Date: 2008 Nov 09, 11:10 -0800

    Robert:
    
    Thanks for the information on the Ball drop sextant. It sounds like it
    was a beta version of an artificial horizon. It was nice to see they
    were trying to improve the concept.
    
    When you used bubble sextants on the water did you use the averaging
    mechanism? 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 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.
    
    Does anyone have any published information on accuracy of GPS at high
    latitudes?
    
    Bruce
    
    Robert Eno wrote:
    > Bruce,
    >
    > It was officially called a "Mark I Ball Recording Sextant". I like to call
    > it the "Kerplunk" sextant.
    >
    > It was an experiment -- one of many in a quest to find the perfect
    > artificial horizon sextant -- that did not work out in practice as it did on
    > paper. In the end, the bubble sextant was the most practical and dominated
    > the field.
    >
    > I own a Kerplunk sextant that is in mint condition. Mine is dated 1944. US
    > Navy Bureau of Ships
    >
    > The sextant works essentially like this:
    >
    > The operator allows the pendulous alidade to swing freely until the observed
    > body is approximately in the centre of the view, upon which he locks the
    > alidade by pulling a trigger mechanism. He then fine tunes the recording by
    > adjusting a fine adjust knob at the same time, squeezing another trigger
    > mechanism which allows lead shot to drop, one shot at a time, onto piece of
    > carbon paper which leaves an impression dot on a graph plate. The observer
    > then examines the graph plate and tries to average out the dots to come up
    > with a number. I am likely not doing a very good job of describing the
    > process but if you want, I can send you a copy of the instructions.
    >
    > Short answer: the Ball Drop Sextant did not live up to it's promise and in
    > fact proved to be too cumbersome and too inaccurate.
    >
    > I have tried bubble sextants and bubble attachments at sea many many times,
    > and have found that bubble horizon observations at sea these yield dubious
    > results; even when the sea is flat-arsed calm. Of course I have all of the
    > data from my past efforts. It's fun to try, but in terms of usefulness, I
    > would question the value of one's efforts unless you simply had nothing else
    > to go on.  Just for your interest, some of the pioneer aviators in the
    > Canadian Arctic (we are talking the 1920's and 1930's) used marine sextants
    > for navigating through the trackless barrenlands. In the absence of a decent
    > DR position, they would land on a lake, set up an artificial horizon and
    > take sun shots. I have a photo of this operation.
    >
    > my two bits' worth.
    >
    > Robert
    >
    >
    >
    > ----- Original Message -----
    > From: "bruce hamilton" 
    > To: 
    > Sent: Sunday, November 09, 2008 1:43 AM
    > Subject: [NavList 6466] Re: sextant without paper charts
    >
    >
    >
    >> Four who actually know how to use the sextant. On coastal merchant ships
    >> it went like this :-)
    >>
    >> The Old man knew everything about the sextant, but didn't tell you.
    >> The First Mate used to know, but was too busy running the ship
    >> The Second Mate knew it for his exams, but forgot the details.
    >> The Third Mate was going to know when after he wrote his exams.
    >> The Navigation Cadet wanted to know, but could not find anyone to teach
    >> him.
    >>
    >> Question: I spent a lot of time sailing the foggy waters around
    >> Newfoundland, and we would often have a sunny day above, but the horizon
    >> was obscured by fog. Does anyone on the list own one of those sextants
    >> that drop a bit of shot to calculate the horizon? I believe the US Navy
    >> had them.Were they any good?
    >>
    >> If the sextant had continued to evolve, I think a gyroscopic base might
    >> have been a good route. I saw one somewhere.Does anyone know about those?
    >>
    >> Did inertial navigation ever make it to the Merchant Navy bridge or is
    >> it still military only?
    >>
    >>
    >>
    >>
    >> frankreed@HistoricalAtlas.net wrote:
    >>
    >>> And three days after I wrote about this on NavList, I see that one Tim
    >>> Queeney blogged about it on oceannavigator.com:
    >>> "The U.S. Navy is well known to be secretive about its nuclear
    >>> submarines.
    >>> [...] But as ON contributor Greg Rudzinski points out, there is one piece
    >>> of
    >>> gear that sub officer's will discuss: the fact that the boat carries a
    >>> sextant. Check out this article on the new U.S.S. New Hampshire from the
    >>> Nashua, New Hampshire Telegraph. One of the sub's officers actually
    >>> admits
    >>> there are only four members of the crew who know how to use this rare
    >>> navigational device. "
    >>>
    >>> A hot topic. :-)
    >>>
    >>>
    >>>
    >>> frankreed@HistoricalAtlas.net writes:
    >>>
    >>>
    >>>
    >>>> Here's an article about a tour of the new Virginia class submarine "New
    >>>> Hampshire" which is almost ready to joing the fleet (the URL below
    >>>> should be
    >>>> all on one line; just in case your web browser or email client doesn't
    >>>> render it that way):
    >>>> http://www.nashuatelegraph.com/apps/pbcs.dll/article?AID=/20081021/NEWS01/310219927/-1/news01
    >>>>
    >>>> Right at the top, the article notes that the submarine carries a
    >>>> sextant,
    >>>> just in case. Later in the article, it's explained that they carry no
    >>>> paper
    >>>> charts.
    >>>>
    >>>>  -FER
    >>>>
    >>>>
    >>>
    >>>
    >>>
    >>
    >
    >
    >
    > >
    >
    >
    
    
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