NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Bubble sextant instructions
From: JC Sutherland
Date: 2001 Dec 12, 5:04 PM
From: JC Sutherland
Date: 2001 Dec 12, 5:04 PM
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.