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Subject: Re: Bubble sextant instructions
From: Cap'n MCL Rodaway (captainrodaway@XXX.XXX)
Date: Fri Dec 14 2001 - 21:42:48 EST
Thanks for the info Clive & everyone else. I have no plans for taking it
with me out to sea, more for fun at the end of the pier. They're just not
as comfortable to handle as a proper sextant.
Yours Aye
Michael Rodaway
Seamen, with their inherent sense of order, service, and discipline, should
really be running the world.
--Anonymous
on 12/12/01 19:04, J.Sutherland at jcs@XXX.XXX wrote:
> Cap'n Rodaway;
>
> I have used the Mk9 sextant for many years. In its
> unmodified form it is of
> little use at sea as it is generally impossible to
> keep the bubble steady
> enough, although I confess I have never tried it
> from the deck of a large ship.
> If the steadyness of the vertical is tolerable,
> then the vibration of the deck
> caused by the engines can be an advantage.
> These sextants are very old now and deterioration
> of the glass surface on the
> inside of the bubble chamber tends to make the
> bubble stick (especially if it
> is small) and the vibration helps in unsticking
> it. Adjusting the bubble size
> is a knack but it is surprising how many of these
> sextants have retained their
> liquid filling
> War surplus sextants were frequently modified by
> removing the bubble chamber
> and adding a prism to arrange a simultaneous view
> of the horizon. I have
> modified (one of the earlier ones that didnt have
> the averaging clock) by
> drilling a hole through the front and replacing
> the 'horizon mirror' with a
> split mirror (to produce the familiar arrangment),
> while retaining the bubble
> for use on land. The biggest problem with this
> arrangement is that the glare
> filters are in the combined light path and only a
> strong horizon combined with
> a weak Sun gives ideal sights.
>
> The sextant Mk IX with the clockwork averaging is
> ideal for back yard
> navigation and accuraces of less than + or - 1
> minute can be achieved with
> practice. Without mechanical averaging it will be
> necessary to take up to a
> dozen sights and average the result by graphing
> the data.
> The small bulbs for illuminating the bubble and
> the scales are very difficult
> to find and even seriously damaged sextants should
> be aquired if only to
> caniballise these bulbs.
> Without them only Sun sights are possible
> The web site below is what you are looking forif
> it is still running. The
> reproduction is poor quality but if you have any
> trouble come back to me and I
> will photo copy my booklet for you.
>
> Have fun!
> Clive Sutherland
> Abingdon UK
>
>> http://www.physics.uq.oz.au/physics_museum/bblsex.html
>
>
>
>
> Cap'n MCL Rodaway wrote:
>
>> I was wondering if any one can point me to a web site or any other source
>> for a instructions on using a WWII RAF Bubble Sextant Mark IX A. Also what
>> differences, if any, are there in working the sight with it, compared to a
>> marine sextant?
>>
>> Yours Aye
>> Michael Rodaway, M.N.
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