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
    Universal Plotting Sheet at High Latitudes
    From: Bob Goethe
    Date: 2018 Apr 5, 04:36 -0700

    VP-OS Universal Plotting Sheet at High Latitudes

    Unless you are at the equator, lines of longitude are always slightly converging.  But we can use a universal plotting sheet because over the space of 2° of latitude, the degree of convergence is not navigationally significant.

    However, I presume that if you go far enough north, the convergence WILL become navigationally significant.

    Through what latitude range is a VP-OS plotting sheet useable?

    I am specifically thinking of a hypothetical voyage through Davis Strait, N 68.75°, W 62.10°, and wondering if a universal plotting sheet can be used for plotting accurate-enough DR positions.


    Using Traverse Table to Directly Calculate a DR

    In looking at the traverse table in Bowditch, it captures a solution to plane right triangles.  Coming up with the difference in latitude seems straightforward.  Assuming I am on a course of 45°, then: 

    ΔLat = DistanceSailed x cos(45°)

    If I want to use that to get a difference in longitude rather than simply a nautical-miles-travelled-from-east-to-west, it appears to me that I could do this with an equation.  This is unfamiliar territory for me and I would appreciate you checking me on my concept.

    Assuming that I am sailing on a course of 45°, and if the departure in nautical miles = DistanceSailed times sine of my course c, then here is my equation:

    departure = DistanceSailed x sin(45°)

    If the width of a degree of longitude in nautical miles = cos(latitude) x 60, then if I am at a latitude of 68° north, it would seem that:

    ΔLong = [DistanceSailed x sin(45°)] / cos(68°)

    Have I got this right?


    Thank you very much.



    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