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    Re: Bubble horizon
    From: Jim Dullea
    Date: 2002 Dec 17, 07:30 -0500

    Now you have my attention...would you be willing to add a little detail to
    just how big the bubble should be and what the relationship between the
    bubble and the observed body should be.  I always thought the correct method
    was to center the body in the bubble but this causes me to create a
    relatively large bubble on the Bendix 5851-1 that I was using.
    
    Jim Dullea
    Tech Marine Business, Inc
    202 675-7782
    dullea{at}tmbhq.com
    
    
    -----Original Message-----
    From: Navigation Mailing List [mailto:NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM]
    On Behalf Of Robert Eno
    Sent: Monday, December 16, 2002 6:33 PM
    To: NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM
    Subject: Re: Bubble horizon
    
    I'd like to add my two bits' worth on this topic because I have worked with
    bubble horizons for quite a few years.
    
    In my experience, the greatest cause of errors, vis a vis bubble attachments
    is due to inherent design flaws.
    
    To make a long story short, unless you can adjust the size of the bubble,
    you will experience errors; sometimes gross errors. Several years ago, I had
    an opportunity to take dozens of sights with a very expensive ($1000 US)
    professional bubble attachment made by a well-known sextant manufacturer.
    This bubble attachment did not have a provision for adjusting the size of
    the bubble. In my estimation, it was not worth the price. It appears to me,
    anyway, that a practice bubble horizon will produce the same results as the
    very expensive "professional" attachment. Save your money.
    
    Contrast this to a C.Plath bubble attachment which does have a provision for
    adjusting the size of the bubble. One can obtain very accurate positioning
    data when using this device. Unfortunately, they are relics of the past. I
    don't think that they have been manufactured since the early 1960's but are
    still available from time to time, from antique and used sextant dealers.
    According to one publication that I have, they were issued to U.S. Navy
    fleet ballistic missile subs as a backup. Can't verify that first-hand
    though so take this with a grain of salt.
    
    Finally, as far as bubble sextants/bubble attachments are concerned, the
    best, the most accurate and the easiest to use, ever, is the RAE Mark IX
    aircraft sextant. It wins hands down in all categories.
    
    Robert
    ----- Original Message -----
    From: Marc Bernstein 
    To: 
    Sent: Monday, December 16, 2002 3:49 PM
    Subject: Bubble horizon
    
    
    > I assume most of us are using the "practice bubble horizon" sold by
    > Celestaire. The key word here is 'practice'. It is not particularly easy
    to
    > sight through and the bubble is quite wobbly. The main problem appears to
    be
    > a lack of fluid dampening. Based upon my experience 7 minutes is not bad.
    I
    > often get accuracies of 10-15 minutes. Maybe I need more practice.
    >
    > By the way if you hold a flashlight in just the right spot, it is possible
    > to illuminate the bubble from the outside so you can use the practice
    bubble
    > at night also. This only works with the Moon. There is not enough light
    > transmission to sight a star, and no magnification.
    >
    > But for those of us who are landlocked it is still worth it.
    >
    
    
    

       
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