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: Graphs of Lunar Distances.
    From: Hewitt Schlereth
    Date: 2010 Oct 24, 23:10 -0400
    Frank -

    Up till the time I taught a group of three guys over a period of five days ashore and five days at sea this past January, I'd have agreed with you. But after five days practice ashore and five days at sea, using our one and only David Mk 15, they were consistently getting sun LOP intercepts of 1', and often even better. We also got excellent results from naked-eye morning and evening horizon sights - again, intercepts of about 1', and sometimes better, so perhaps conditions were exceptionally benign.

    My previous experience with plastic was two years worth of summer-time Atlantic passages with an Ebbco. This was in the '70s, before GPS. My sense then was that the Ebbco was producing sun LOPs of around 2'. But the only check I had was from known positions ashore.

    The difference between then and January 2010 was my hand-held Garmin 72. Honestly, I was amazed. The only real difficulty we encountered was with stars. But that was cured by removing the 'scope and just sighting through its mounting rings.

    Anyway, now that I've dipped a toe in, I'll be trying more lunars in the future, to test things further.

    -Hewitt

    On Sun, Oct 24, 2010 at 10:34 PM, Frank Reed <FrankReed{at}historicalatlas.com> wrote:

    Hewitt, you wrote:
    "Error in Lunar: 0.9'
    Approximate Error in Longitude 28.3'."

    When I have used a Davis sextant for lunars my results had a range of roughly
    +/-2.5'. Sometimes, of course, you can do better just by chance, but in general, inexpensive plastic sextants are not suited to accurate lunars. They're great sextants within that expected range. You can sail oceans with them, no problem, if a couple of minutes of arc is not a serious concern as in traditional small boat line of position navigation.

    And you wrote (to Douglas):


    "This is interesting to me on two counts. First my results are in line with yours, which is heartening. "

    Seven out of eleven of Douglas's Jupiter lunars were within +/-0.22 minutes of arc --so your results are not actually in line with his. He has concluded that his lunars are much worse than this apparently because there is some kind of bug in his calculator clearing method.

    -FER


    ----------------------------------------------------------------
    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
    ----------------------------------------------------------------


       
    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