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: Art and Navigation
    From: Hewitt Schlereth
    Date: 2015 Mar 26, 16:17 -0700
    Over the years I've had good results with plastic sextants.

    The first two years I actually did celestial on offshore passages I used an Ebbco Mk1 which was fine for sun and moon. After that, I got an aluminum sextant with big mirrors and started taking stars routinely.

    Greg did an exhaustive set of trials of an Ebbco last summer and his results confirm the utility of plastic. You've got to fuss more, be a hawk about side and index error, but the results are nothing to be ashamed of.

    Now that I'm teaching here in San Diego I'm finding the students who have sextants (about half) have Davis 15s or 25s. 

    I have one of each, plus a Mk3 and am getting results with the Mk3 on a par with the two micrometer drum models. Oddly enough, on the drum models, I get just as good results with the sight tubes as the scopes,.

    One of the students in the most recent group preferred to bring the center the of sun to the horizon. That way, there is no semi-diameter correction. (Poof! goes one table from which to pick the wrong number.) I remembered seeing this in an old British text but had never tried it. So I did, and it worked fine.


    On Mar 26, 2015, at 11:26 AM, Greg Rudzinski <NoReply_Rudzinski@fer3.com> wrote:


    I agree that trying to keep a sextant's index error exactly at zero is futile but this should not be an excuse for never adjusting the horizon mirror. Carly's Mark 3 without a case will be very demanding on index error stability. I will suggest a plastic food container fitted with customized foam as something to try. 


    If you post all your sight reduction data (a picture of working notes should be good enough) then we can check things out. 


    Greg Rudzinski


    From: Tom Sult
    Date: 2015 Mar 25, 11:15 -0700

    The goal is not to zero your sextant, but to know the error. I like my sextant to have several min of error ON the arc. Trying to be exactly zero is hard and rarely lasts. Testing error before a round of sights then adding or subtracting it is more practical. 

    Tom Sult, MD
    Author: JUST BE WELL

    View and reply to this message

    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