NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: The development of bubble sextants
From: Gary LaPook
Date: 2009 Aug 18, 12:06 +0200
From: Gary LaPook
Date: 2009 Aug 18, 12:06 +0200
I've never seen one of these for sale on ebay nor have I ever seen a mention of it in any navigational manual. Just because you can get a patent for something doesn't mean it will work. gl Hanno Ix wrote: > Gentlemen: > > Please refer to: > > US Patent 1,912,358 > V. Bush: Apparatus for establishing an artificial datum > Filed April 8, 1928 > > The inventor means an artificial horizon. Please refer to the > attachments for the drawings. > > He has implemented a mechanical lowpass filter. We have discussed LP's > before. Better yet: This filter simultaneously works in 2 coordinates, > roll and pitch. > > He also points out that the natural oscillating frequency of the > mirror should be as "low as possible" but he doesn't give any data. > Since the roll frequency of ships is rather low to begin with (judging > from you-tube: about. 0.1 Hz = 1 period per 10 sec for an oil-tanker ) > the filter has to have a cut-off frequency of about 0.01Hz which > amounts to 1 period per 100 sec. The filter also needs to be > sufficiently damped. The reason is simply avoiding resonant > oscillations of the filter/mirror in response to the ship's movements. > To build an LP of this kind is the challenge! > > The inventor has made every effort to decouple the housing of the > mirror from the body of the sextant. So to speak, he created something > like a bubble level floating within bubble level. > > With a lowpass of this kind, influences from pitch/roll would be > reduced by a factor of 100, possibly more. So, a 10 degree roll would > create 0.1 degree (6 arc-min) deflection of the mirror. Smaller ship > will have higher roll/pitch frequencies than oil-tankers, maybe 0.5 > Hz. Accordingly, on smaller ships 1 arc-min oscillation of the mirror > might be possible. Is that error sufficiently low given the > circumstances? It is certainly much less than I saw once in a bubble > sextant. > > Perhaps most importantly, this patent points out how to separate > accelerations of the sextant which are instantaneous from gravitation > which is constant in time. > > When I made my proposal with the tubular ring the other day I had > similar ideas in mind, however I had not fully understood the > interaction between bubble and spirit. > > Regards > > > > > > > ------------------------------------------------------------------------ > > > ------------------------------------------------------------------------ > > > ------------------------------------------------------------------------ > --~--~---------~--~----~------------~-------~--~----~ NavList message boards: www.fer3.com/arc Or post by email to: NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---