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
    Re: Puzzle
    From: Richard B. Emerson
    Date: 2000 Sep 13, 10:11 AM

    Anthony writes:
     > I think (conclude) that your original thought of time being in error
     > was correct.  Yesterday I ran a curve fit on your Betelgeuse hs data
     > and came up with reasonable results for UTC time exactly 8 minutes LATER.
     > Consider:
     >         UTC             Tow/Away
     >         ---             --------
     >         09:36:29        1.7 A
     >         09:37:34        2.6 T
     >         09:38:34        2.4 T
     > There appears no doubt that you were observing Betelgeuse because of its
     > brightness in that portion of the sky. (the question was raised earlier
     > by someone).
     > I also examined your other body sights closely and find they are as good
     > as one could expect from your platform.
     > Also: with the altered time on Betelgeuse fits well for any Fix using
     > bodies 2-3 and 1-2-3
    As the above suggests, the three rounds of sights for Betelgeuse,
    Jupiter, and the Moon do, in fact work plausibly.  The difference
    between the AP and the final fix is about 4nm to the SW which, in
    ocean sailing terms, is pretty good.  Even for coastal work, given the
    boat was moving on a course of 237M at just under 6 knots and there's
    about 30 minutes between the first and last sights, this is pretty
     > How you may have arrived at a time with 8 minutes difference is in your
     > ballpark! :)  I could only make a wild guess because your hack method
     > is strange to me.
     > Any further reflections?
    Now, how did the timing error happen?  I can think of any number of
    scenarios but most are ruled out by conflicting information.  For
    example, the stopwatch never stopped running and it loses time over a
    much longer period than ten to twenty minutes.  It's a mechanical
    watch and the second hand is easy to read.  The watch wasn't dropped
    and it performed well later as well as on other days.  One thought did
    occur to me.  A possible explanation hinges on how was the timing
    done.  That's done by starting the stopwatch at a known, accurate time
    and noting that time.  The obvious differences of something divisible
    by 10 just don't work.  That is, being off by 10, 20, or 30 minutes
    and adjusting accordingly gives errors in excess of those seen in the
    latter two series.  Of all the remaining choices (e.g., being off by
    1, 2, or 3 minutes), 8 minutes seems the most likely choice because
    the stopwatch was started from an LCD display on a GPS receiver.  It's
    *possible* that I read 09:28:00 for 09:20:00 or simply wrote down
    09:20 (although I doubt that).  To avoid ambiguity, I put a slash
    through my zeros so they're not mistaken for 6's or 9's.  The time
    09:20 is very clearly written *but* if it's clear but wrong...?
    Unfortunately, there's no way of being certain this is what happened
    and this brings me back to the main reason for asking the question.  I
    wasn't so much concerned about retrieving a series of sights for their
    own sake.  Clearly we made it into Cape May and didn't need someone
    holding our hands to do so.  I asked the question to examine a
    situation where there's a set of internally consistant sights which,
    for some reason, are simply wrong for the boat's position.  How does
    one *confidently* resolve such an error?  I hope everyone else has
    learned as much from this exercise as I have.  Again, my thanks to
    everyone who contributed and thanks to Tony for some very good
    "outside the box" thinking.
    S/V One With The Wind, Baba 35

    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