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: Sextant accuracy and possibility of future improvement
    From: John D. Howard
    Date: 2016 Jul 21, 14:14 -0700

    More thoughts on the sextant as used at sea.

    The one thing that makes the sextant a great instrument to use at sea is that when you use it you are looking at the horizon. Our brain and inner ears talk to one another and tell us when we are upright or not. On a boat that is not only rolling but bouncing around we can get disorientated but a sight of the horizon will usually help us figure where we are (which way is up).

    I am a pilot, not a sailor but the problems of disorientation are very similar. When doing training for instrument flying you usually have on your head some sort of vision restricting device (under the hood). One way to cheat is to get a glance of the horizon - one peek is worth a thousand crosschecks. My point is that when using a sextant the sun or star may be a bright small dot but the horizon is big and all around you. The boat may roll and you lose sight of your star but as soon as the horizon is visible you can re-acquire the star very quickly.

    Not having done a lunar I do not know for sure but I suspect that they cannot be done in rocking, bouncing weather. There are already binoculars and telescopes that you can point to a star, press a button and it will tell you the angle but I think such a device would be hard to do at sea.

    Aircraft sextants with the bubble are used different than a marine sextant. When taking a sight you get the star or sun in the eyepiece - bubble then at a pre-figured time you hit a button. You keep the star in the bubble the best you can for usually two minutes. The sextant then averages the position over the whole two minutes. Almost backwards from a marine sextant where we take one shot at one time - do it many times then average the many single shots.

    Perhaps combine many of these ideas. Have an electronic inclinometer along with a rotary sensor and digital readout but average one sight over a long time while looking at the real horizon.

    John H.

       
    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