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: Alain Gerbault logbook
    From: Paul Bedel
    Date: 2019 Jan 11, 06:35 -0800

    Hi Lars and thank you very much for your very interesting posts. Here are other developments about Gerbault's calculations.

    The formula used in "Johnson's Tables" maybe something like: hav(HA) = [hav(90°- Alt) - hav(colat - PD)] / [hav(colat + PD) - hav(colat - PD)] = A/B where PD is the polar distance 90° - dec. This formula was found by H. B. Goodwin in 1910 and discussed in the "Nautical Magazine". Logs of A and B can be found directly in a double entry table correctly arranged with direct and complementary arguments. Following your idea, a constant (about 0.7276) is added to the logs.

    Gerbault made his observations at about 22h 10 civil local time. How did he see the horizon line ?... the moon first quarter was on 1st of april!

    I think so the tables used are not from A. C. Johnson (1828-1909) who was Naval Instructor in the Royal Navy and not sub-lieutenant, so I'll try to have more informations on Gerbault and his methods of navigation. First, I'll re-read his books about his Atlantic crossing and first circumnavigation: "Seul à travers l'Atlantique" (1924), "A la poursuite du Soleil" (1929) and "Sur la route du retour"(1929).


    Paul, 48° 40' N, 1° 59' W.

    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