Welcome to the NavList Message Boards.


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

Compose Your Message

Add Images & Files
    Re: Bubble sextant construction
    From: Hewitt Schlereth
    Date: 2013 Mar 21, 17:25 -0700

    On my Mk IX-A I have found a bubble about twice the size of the sun works 
    well. I keep the bubble in the center of the field and the sun in the center 
    of the bubble. Against GPS locations, intercepts are 2-4 nautical miles.
    Sent from my iPad
    On Mar 21, 2013, at 4:38 PM, "Paul Brewer"  wrote:
    > In the case of the RAF Mk IX series of sextants the diaphragm was used to
    > increase the volume of the chamber assembly. There is a reservoir connected
    > to the bubble chamber and eventually this is emptied and air is fed to the
    > chamber. The size of bubble could be controlled by the deflection of
    > the diaphragm. In that type of arrangement there would be essentially no
    > pressure difference from no bubble to full bubble. Some of the American
    > chambers did increase or decrease pressure on a sealed system to change the
    > size of bubble.
    > As to bubble size, too small a bubble  can make it slow to react. The
    > official guides for the MkIX suggest a bubble size but within a fairly
    > large range. I personally try to match my bubble to my target when I am
    > calibrating but I have little experience with taking sights in anger.
    > Paul.
    > On 21 March 2013 14:38, Randall Morrow  wrote:
    >> ------------------------------
    >> Can antone tell me how the older sextants change bubble size? Was it with
    >> application of pressure or by addding-subtracting volume of fluid? Some old
    >> drawing I have seen suggest a bellows for pressure. Also, how much of a
    >> difference in accuracy is gained by matching bubble size to the body
    >> observed? If it is significant, why do the post WWII versions not have
    >> bubble adjustments?
    >> Thanks.
    >> ----------------------------------------------------------------
    >> NavList message boards and member settings: www.fer3.com/NavList
    >> Members may optionally receive posts by email.
    >> To cancel email delivery, send a message to NoMail[at]fer3.com
    >> ----------------------------------------------------------------
    >> View and reply to this message: http://fer3.com/arc/m2.aspx?i=123020
    > --
    > I am testing Gmail.
    > My Main Email address to which you should reply is
    > paul---co.uk
    > I check that one at least daily when I am at home.
    > View and reply to this message: http://fer3.com/arc/m2.aspx?i=123024

    Browse Files

    Drop Files


    What is NavList?

    Join NavList

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

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

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

    Email Settings

    Posting Code:

    Custom Index

    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