Welcome to the NavList Message Boards.

NavList:

A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Message:αβγ
Add Images & Files
    Name or NavList Code:
    Email:
       
    Reply
    Re: The development of bubble sextants
    From: Hanno Ix
    Date: 2009 Aug 17, 20:57 -0700
    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.navlist.net
    Or post by email to: NavList@navlist.net
    To , email NavList-@navlist.net
    -~----------~----~----~----~------~----~------~--~---

    File:


    File:


       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    NavList is a community devoted to the preservation and practice of celestial navigation and other methods of traditional position-finding. We're a group of navigators, navigation enthusiasts and hobbyists, mathematicians and physicists, and historians interested in all aspects of navigation but primarily those techniques which are non-electronic.

    To post a message, if you are already signed up as a NavList member, start a new discussion or reply to any posted message and use your posting code (this is a simple low-security password assigned when you join). You may also join by posting. Your first on-topic messsage automatically makes you a member, and a posting code will be assigned and emailed to you for future posts.

    Uniquely, the NavList message boards also permit full interaction entirely by email. You can optionally receive individual posts or daily digests by email, and any member can post messages by email (bypassing the web site) by sending to our posting address which is "NavList@NavList.net". This functionality is similar to a traditional Internet mailing list: post by email, read by email, reply by email. Most members will prefer the web interface here for posting and replying to messages.

    NavList is more than an online community... more about that another day.

    © Copyright notice: please note that the rights to all messages and posts in this discussion group are held by their respective authors. No messages or text or images extracted from messages may be reproduced without the explicit consent of the message author. Email me, Frank Reed, if you have any questions.

    Join / Get NavList ID Code

    Name:
    (please, no nicknames or handles)
    Email:
    Do you want to receive all group messages by email?
    Yes No

    A NavList ID Code guarantees your identity in NavList posts and allows faster posting of messages.

    Retrieve a NavList ID Code

    Enter the email address associated with your NavList messages. Your NavList code will be emailed to you immediately.
    Email:

    Email Settings

    NavList ID Code:

    Custom Index

    Subject:
    Author:
    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site