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: Precomputing sextant observations at sea
    From: Gary LaPook
    Date: 2014 Jan 28, 16:32 -0800
    Here is an excerpt from his book which shows him using both pecomputed altitudes and ones freshly worked on this Bygrave slide rule.


    From: Francis Upchurch <francisupchurch@gmail.com>
    To: garylapook@pacbell.net
    Sent: Monday, January 27, 2014 10:33 PM
    Subject: [NavList] Re: Precomputing sextant observations at sea

    Thanks to Douglas Dennny for sending the Chichester observer book extract. Looking at the original chart (from Hughes,also in Chichester' 2 books, Lonely Sea and Sky and Alone across Tasman Sea) with all the pencil markings, including wind drift etc, I still have 3 main questions.
    1) how did he get the exact position of his "square box fixes" on some of the LOPs?
    2) why did he need to use the Bygrave to calculate new LOPs mid flight if he already had them prepared? (I now think the answer is that he needed to do extra "pre-computed" LOPS at e.g. 0400GMT and did these before 0400, so needing new Bygrave calculations. What do you think Gary?
    3)How did he work out the bearing from the turning point to Howe Is along the final LOP? His pencil markings (bottom left) give bearing 193.3degs resulting from calculation 180+24..3=204.3,-11(?variation 11E?)=193.3degs.I thought the true bearing would have been Az(68degs) +90deg=158deg true. Could anyone explain his calculation? I must be missing something basic! Good job he didn't or he would have missed and drowned!
    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

    Attached File:

    (Chichester-navigationhughes.pdf: Open and save or View online)

    View and reply to this message: http://fer3.com/arc/m2.aspx?i=126735


    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