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Subject: Re: Bubble horizon
From: Robert Eno (enoid@XXX.XXX)
Date: Mon Dec 16 2002 - 18:32:56 EST
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 <marc.bernstein@XXX.XXX>
To: <NAVIGATION-L@XXX.XXX>
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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