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    A-12 etc.
    From: Bruce Hamilton
    Date: 2008 Sep 04, 00:19 -0700

    Well, I just received my second bubble sextant in the mail. It was an
    A-12 and it looks new.  I suspect it might be a Celestaire re-build as
    it looks so new, and regular batteries fit. I was all ready to take it
    to work and trim the battery holders down a bit on the lathe, but I
    won't have to.  It came with 2 working bubble sets, and the only thing
    I  might improve is the bubble size, so I will order some Xylene later
    this week. Any recommendations on the perfect bubble size to shoot for?
    
    It was overcast tonight, but I took it out and tried it a bit and peeked
    a a few stars. I have a lot of light pollution where I live,but the
    superimposed bubble is great.  I spent a few years being taught how to
    line up one small round object in a bigger round object, but this
    process doesn't leave me with ringing ears and a sore shoulder. Ah, the
    joys of a steel butt plate.
    
    
    I can see why I was cautioned about getting a bubble sextant by list
    members. They are brilliant machines and you can't buy just one. I can
    also make sure my apartment has not moved, just by stepping out on the
    balcony. I did a LOP with the A10 the other evening with a sun shot a
    half hour before sunset and was 0.87 NM from my AP, which was my actual
    position taken from Google earth. (More luck than skill).  I figured out
    its index error using a distant bridge.  I hope to take both of the
    sextants down to my local surveying shop and pop them in front of the
    horizontal collimator. The fellow in the shop seems to like madmen like
    myself who insist on using antiques to get around in this GPS age. I was
    fascinated to hear that they get accuracies of 2 cm with a proprietary
    GPS system they use now.
    
    I would like to try a bubble sextant on a ship some day. The biggest
    ship I ever worked on would hardly roll at all on a calm day, and even
    less with a load of iron ore!  I used to practice sun shots on my first
    ship, a salty little 315 foot coastal freighter, and always wondered how
    people managed to do it on a sailboat in weather.I used to work out
    distance off by verticle angle with any handy lighthouse, or other
    object of known height, and found that to be quite accurate. I never did
    much horizontal angle work, but an old classmate who is a coast guard
    officer says they still double check all buoy positions that way.
    
    I had asked where Radio Direction finders went as they were the cheap
    backup when I last pleasure sailed in the mid seventies.  I see that the
    technology has been dropped by pleasure boaters, and can only find old
    sets. The modern commercial sets look great and give you an instant
    readout calculated from 4, or more antennas. No more seeking the null.
    Hams use them too. I used the Marconi RDF on the first ship I was a
    cadet on, and it was pretty handy when the loran-c chains were acting
    up, and there was nothing on the radar close enough to give a good range
    and bearing.  I have dim memories of applying some sort of corrections
    for far away stations. The correction sheet looked like sine wave. I'll
    have to look it up in Bowditch. It was great as you would find a strong
    station get a bearing and there you were with a bearing and something to
    listen to as well as it picked up many bands.  Aircraft still have ADF,
    but like all avionics, they are pricey. The Grampion 30 that I sailed
    from Thunder Bay Ont to Georgian Island had nice portable RDF on it. I
    think it was the Gladding Cyclone pictured on the page below.
    
    
    
    Here's a page of old RDFs.
    
    http://www.angelfire.com/space/proto57/rdf.html
    
    
    Here's a great article on Celestial from an airbus pilot.
    
    http://www.airspacemag.com/flight-today/celestial.html
    
    Thanks again for all the information. I enjoy reading everyone's posts.
    
    Other projects I have in mind. I just got 3 microscope slides so if
    anyone has some good pages on the Briss sextant, please send it to me.
    
    Once Gary has recovered from his trip, I look forward to his posting the
    information on the Byrave sextant as constructing one is going to be a
    winter project for me. Here in Vancouver BC, we might not see the sky
    for months on end so I need something to do other than work through
    celestial nav examples.
    
    
    Bruce Hamilton
    Vancouver, BC
    
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