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    Re: Lunar Distances: Graphic Methods
    From: Henry Halboth
    Date: 2004 Apr 24, 16:53 -0400

    The most significant difficulty I experienced in observing Lunars at sea
    was in perfecting contact between the bodies. With the attendant ship
    movement it just is not possible to maintain sufficient steadiness to
    perfect that contact, as one might do when using a sextant stand or
    otherwise somehow supporting the instrument - consequently, in my
    experience at least, it became necessary to sweep (maybe thats not the
    right word) the contact by canting the sextant while adjusting the angle,
    much as one does in perfecting horizon contact in taking an altitude. It
    seemed to boil down to taking the reading on the fly, which never felt
    too secure.
    
    I might note, in this regard, that there does not seem to have been any
    recent mention of the use of a sextant stand in taking shoreside
    artificial horizon altitudes, as was done by the hydrographical surveyors
    in establishing positions - the sextant stand is pretty well covered in
    "Hydrographical Surveying", by Wharton & Field, 1920 Edition, and might
    be of interest to those using the artificial horizon. This is pretty much
    the standard work, and might be useful to those seeking more theoretical
    accuracy than sometimes sought in practical navigation - by the way, it
    doesn't even mention Lunars.
    
    Perhaps lifeboat navigation will come up at a later time.
    
    On Sat, 24 Apr 2004 13:21:36 EDT Frank Reed  writes:
    > Heny H wrote:
    > "It was not my intent to advocate any method of solution as respects
    > any
    > navigational problem"
    >
    > I didn't interpret that you were advocating any method.
    >
    > And:
    > "There have been enough methods of solution to satisfy most any
    > taste in
    > celestial navigation, however, in the final analysis, practical
    > skill in use of
    > the sextant, or whatever, becomes the governing factor, whether it
    > be in
    > measurement of altitude, lunar distance, horizontal angle, or
    > otherwise, as no method
    > will correct for a bad observation."
    >
    > Or a bad sextant, or a badly adjusted sextant... One of the things
    > I've
    > noticed when people first start shooting lunars is that they are
    > surprised by the
    > quality problems they encounter (there are a couple of these on the
    > list
    > today). Often it's not an observational problem per se, but a
    > sextant adjustment
    > problem. Do you remember anything like that when you experimented
    > with lunars on
    > your South Atlantic passages?
    >
    > And wrote:
    > "I seem to remember it having been Bowditch's intent to reduce the
    > mathematics of
    > navigation to the understanding of every seaman aboard his ship
    > -including
    > the cook - although I do question his success rate."
    >
    > The story of the cook is famous and it's in the intro to modern
    > editions of
    > Bowditch. It seems likely to me that Bowditch, or his publisher, was
    > as much a
    > salesman and promoter as a mathematician and navigator. It is surely
    > true that
    > you can teach anyone to shoot and reduce lunars or any other
    > celestial sight.
    > But why? Who needs a ship full of lunarians? When you think about it
    > in p.r.
    > terms, though, it makes sense. A story like that sells books. It
    > also helps to
    > establish the idea that Bowditch's lunar method is easier than the
    > rest (if
    > even a cook can do it). Many people interested in navigation still
    > believe
    > today that this was Bowditch's contribution --an easier method of
    > reducing
    > "difficult" lunars. The case that it is really easier in any
    > practical sense is very
    > weak. There are many, many "easy" methods, and most of Bowditch's
    > lunars
    > methods were borrowed or lifted from other works with minimal
    > attribution.
    >
    > And wrote:
    > "I also was not aware that we were going to start a thread on
    > lifeboat
    > navigation"
    >
    > Well, that was just a little joke. I thought about putting a
    > 'smiley' next to
    > it, but in this case I felt it was clear that it was just a funny. I
    > had this
    > image of a navigator hauling one of those large celestial globes
    > over the
    > side as his ship is going down. Hey, if it's made of the right
    > material, it might
    > float on its own!
    >
    > And Henry H wrote:
    > "on the subject of which I may have a few earthy comments - my
    > sextant box is
    > still fitted for backpacking while going down a manrope in a heavy
    > sea."
    >
    > I, for one, would love to hear more about this. Did you ever find
    > yourself in
    > desperate circumstances taking celestial sights from a lifeboat??
    >
    > Frank E. Reed
    > [ ] Mystic, Connecticut
    > [X] Chicago, Illinois
    
    
    

       
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