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
Message:abc
Add Images & Files
    or...
       
    Reply
    Re: Bowditch Table 15
    From: Jim Thompson
    Date: 2005 Jan 24, 12:29 -0400

    I look forward to the explanation too.  I have never been comfortable with
    Table 15.  I just spent the morning working paper examples and searching the
    Nav-L archives for prior discussions about Table 9, but it remains unclear.
    My muddle is posted here, but I will fix it when I understand what is going
    on, so expect this page to evolve:
    http://jimthompson.net/boating/CelestialNav/CelestNotes/Bowditch15.htm
    
    Is the entering value (H-h) supposed to be the difference between the height
    of the object above sea level (say a 100' lighthouse) and the height of eye?
    
    When I do drawings, the vertical angle that an observer would shoot between
    the top of an object over the horizon and the horizon has to increase for
    decreasing height of eye as the observer climbs down a 100' mast, but the
    table suggests that vertical angle increases (keep "Distance by Vertical
    Angle" constant, and change [H-h] appropriately as you look at Table 15).
    
    The solution ""Distance by Vertical Angle" cannot be the geographic range,
    or distance between observer and object over the surface of the earth: I ran
    some examples by adding distance to the horizon for an observer at various
    heights of eye, to the distance from horizon to a 100 ft lighthouse.  But
    "Distance by Vertical Angle" cannot be the distance from horizon to the 100
    ft lighthouse either, according to my examples.
    
    To further confuse matters, see the difference in definition for the
    entering value height of object in the NGIA online calculator at
    http://164.214.12.145/NAV_PUBS/APN/Tables/T-15.pdf.  I emailed NGIA to
    obtain their underlying formula for that calculator.
    
    Jim Thompson
    jim2{at}jimthompson.net
    www.jimthompson.net
    --------------------
    Outgoing email scanned by Norton Antivirus
    
    > -----Original Message-----
    > From: Trevor J. Kenchington
    > ...I am having trouble with Table 15...
    
    
    

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    Join NavList

    Name:
    (please, no nicknames or handles)
    Email:
    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:

    Email Settings

    Posting 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