Welcome to the NavList Message Boards.

NavList:

A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Message:αβγ
Add Images & Files
    Name or NavList Code:
    Email:
       
    Reply
    Re: 1984 Bowditch question
    From: Stan K
    Date: 2016 Jul 26, 13:44 -0400
    Yes, Robin.  Those are the "exact" and "approximate" formulas I was concerned with.  My issue was with the statement in the current Power Squadrons Junior Navigation and Navigation courses, which only give the "approximate" formula, where it says to use the formula in Bowditch if the "approximate" formula yields a dip greater than 200' (3º20').  Apparently the "approximate" formula was in earlier editions of Bowditch, with the "exact" formula in later editions.  I felt that the Power Squadrons course materials needed to be more specific as to which editions of Bowditch could be used.  After I learned that the 1984 Volume I showed the "exact" formula (thanks, Frank), I found that the 1981 Volume II seemed to be the first to show it, the 1977 (and earlier) Volume I showing the "approximate" formula.

    So my concern was not with how exact the "exact" formula is, though it is claimed that it is "exact" for the refraction model adopted.  My concern is only to make the Power Squadrons course materials more useful.

    Stan


    -----Original Message-----
    From: Robin Stuart <NoReply_Stuart@navlist.net>
    To: slk1000 <slk1000@aol.com>
    Sent: Tue, Jul 26, 2016 12:37 pm
    Subject: [NavList] Re: 1984 Bowditch question

    Not only do the number of decimal places in the constants not make sense but the use of an explicit arctangent function, in what Stan refers to as the “exact” formula, for typical small dip short angles is quite unnecessary and misleading in terms of overall accuracy. In the attached pdf I suggest where the arctangent may have come from.
    Robin Stuart


    Attached File:

      

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    NavList is a community devoted to the preservation and practice of celestial navigation and other methods of traditional position-finding. We're a group of navigators, navigation enthusiasts and hobbyists, mathematicians and physicists, and historians interested in all aspects of navigation but primarily those techniques which are non-electronic.

    To post a message, if you are already signed up as a NavList member, start a new discussion or reply to any posted message and use your posting code (this is a simple low-security password assigned when you join). You may also join by posting. Your first on-topic messsage automatically makes you a member, and a posting code will be assigned and emailed to you for future posts.

    Uniquely, the NavList message boards also permit full interaction entirely by email. You can optionally receive individual posts or daily digests by email, and any member can post messages by email (bypassing the web site) by sending to our posting address which is "NavList@NavList.net". This functionality is similar to a traditional Internet mailing list: post by email, read by email, reply by email. Most members will prefer the web interface here for posting and replying to messages.

    NavList is more than an online community... more about that another day.

    © Copyright notice: please note that the rights to all messages and posts in this discussion group are held by their respective authors. No messages or text or images extracted from messages may be reproduced without the explicit consent of the message author. Email me, Frank Reed, if you have any questions.

    Join / Get NavList ID Code

    Name:
    (please, no nicknames or handles)
    Email:
    Do you want to receive all group messages by email?
    Yes No

    A NavList ID Code guarantees your identity in NavList posts and allows faster posting of messages.

    Retrieve a NavList ID Code

    Enter the email address associated with your NavList messages. Your NavList code will be emailed to you immediately.
    Email:

    Email Settings

    NavList ID Code:

    Custom Index

    Subject:
    Author:
    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