NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Bubble sextant instructions
From: Capn MCL Rodaway
Date: 2001 Dec 14, 7:43 PM
From: Capn MCL Rodaway
Date: 2001 Dec 14, 7:43 PM
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@CWCOM.NET 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.