NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Bubble horizon
From: Jim Dullea
Date: 2002 Dec 17, 07:30 -0500
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@tmbhq.com -----Original Message----- From: Navigation Mailing List [mailto:NAVIGATION-L@LISTSERV.WEBKAHUNA.COM] On Behalf Of Robert Eno Sent: Monday, December 16, 2002 6:33 PM To: NAVIGATION-L@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 BernsteinTo: 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. >