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
    Davis and Astra head to head
    From: Randall Morrow
    Date: 2013 Mar 4, 07:25 -0800

    The topic of metal versus plastic comes up form time to time so I did a head to head comparison to satisfy my curiosity abotu how much diffrence there was. Though I am the only tester I have taken over 3,300 observations in the last 2-3 years so it is probably as good as any.

    Index corrections checks for the Davis were done the night before with a star, using 6 pairs of sights, each pair turning in opposite directions,and then averaged. The result was
    -8.4. The next day 3 sun sight IC checks showed and average of -8.0. The Astra IC was done witgh three sun sights that averaged +0.4. I have always found index correction sights to be inconsistent with the Davis so extra care was taken.

    Fifteen consectuive LL sun sights were done with the Davis using a mirror artificial horizon. The average intercept was 6.5 nm. The range was 3.6 minutes, from a low of 4.6' to a high of 8.2'. Every sight was "away".

    Only 12 sights were done with the Astra because I expected good results. Six were taken with the standard 3X scope with and average intercept of 0.4 nm. Another six with the 7X scope averaged 0.6 nm. The reange was 0.9', from 0.1' to 1.0'. There was only one "away". I was surprised that the 3X scope results wre pooere than the 7x, but thia is not typical.

    The preponderance of "away" sights is liekly a personal bias toward how I percieve tangency throgh the scopes. The Davis always appears to me to have optical distortion of the shape of the sun disc as you approach tangency.

    It appears the Davis is very consitent, though clearly not as accurate as the Astra. The reslults are certanly good enough to take you anywhere you might want to sail to. The metal frame was an order of magnitude better and though the stability of the metal frame and arc is a factor, I suspect that the quality of the optics may also be important. The more sights I take the more I am convinced that it is the observation, or the perception of what you see or think you see through the scope that is the dominant factor in accuracy.

    If anyone is interested I can post the sight data some other time. Randy
    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

    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