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: Beating a Dead Horse (aka Worley's Sextant)
    From: Brad Morris
    Date: 2014 Feb 2, 15:36 -0500

    Hello Seb

    Firstly, congratulations on surviving the boat journey.  I dearly loved the footage and the reenactment.  Brilliant!

    In reference to Worsley's log you make mention of the copy by James.  It may astonish you (maybe just a little bit) but I managed to track down the original log, now reverentially preserved in a museum.  So its Worsley's navigation, in Worsley's own hand.  George and I were frankly astounded.  George and I struggled with how to publish this information without descending into the navigational terminology weeds.  As George Huxtable is no longer with us, I have refrained from publishing such that a suitable period has passed.  It may finally be time.

    Frank Worsley navigated by the Time Sight method.  Even though Sumner had discovered the modern method of Line of Position (LOP) nearly 50 years earlier, Worsley did not bother with that graphical method when a much more traditional and numerical method was available. 

    The Time Sight method begins with the noon sun in the determination of latitude.  Used for hundreds of years prior to the heroic journey, this method finds the greatest altitude of the sun at meridian crossing.  Then, knowing the declination of the sun (for the day of the year), one can discover the latitude.  The longitude may be found by taking the altitude of the sun in early morning or late afternoon.  The sextant is essentially turned into a sundial.  Through a calculation that depends upon knowledge of the latitude and the (for the period) GMT, the numerical value of the longitude is found.  In combination, daily knowledge of the latitude and longitude may be had.

    The Time Sight method 'advances' each previously found latitude to discover the longitude.  

    Worsley's log can be summarized by the following (1) Time Sight Navigation, when the sun was available (2) Dead Reckoning, when the sun was not and (3) calculation of the distance to South Georgia Island.

    Worsley was most concerned about Cape Belsham.   Cape Belsham is a prominent location on Elephant Island and was noted in several Sailing Directions well prior to 1914.  The latitude and longitude of Cape Belsham was given in those Sailing Directions, but which land mass was it?  From the camp, it was hard to tell. Why was Worsley so concerned?  Because this would provide a reset to his imperfect knowledge of longitude, specifically with the rate of chronometers exposed to cold temperatures.  Knowing the location of the camp to Cape Belsham would allow him to provide a reference for the chronometer, a well respected tradition when ashore.

    Worsley was also concerned with Bird Island, a small islet near South Georgia Island, because they intended to navigate around it on the way to the whaling station, a plan abandoned in the face of peril.

    That's the summary, for explicit details, I'm afraid you'll have to wait.  The above should be enough of a summary for a layman to get a sense of how Worsley navigated.

    I have some questions for you about the recreation:
    1) in regards to the navigation, did you perform noon sun (meridian crossing)?
    2) was the navigation the modern LOP fix which uses multiple bodies around civil twilight to simultaneously determine latitude and longitude? 
    3) did you start out with perfect knowledge of your position on Elephant Island (latitude and longitude)?  Shackleton and Worsley did not!
    4) why did you use a micrometer sextant when Worsley navigated with a vernier sextant?

    As to the markings on "the" sextant, I have been in correspondence with Pippa Hare (Secretary of the James Card Society) who has promised to look into it for me.  I am patiently waiting.



    Seb here, I've really enjoyed reading your posts and I am delighted to see mention of my website pages. I would like to address various points raised:

    1. I would like to add more detail to my navigational instruments however my duties with the RN have prevented that from happening.

    2. Shackleton Epic Expedition did indeed refer to Worsley's Log; a copy of which was kindly given to us by the James family (who recently donated the actual almanac used during the voyage to South Georgia Museum). For many years I've tried to 'decode' Worsley calculations. If any of you fine gentlemen has done so already, I would be delighted to add that information to my website if you're...with full acknowledgement of course. The tricky part is making this information available in 'layman terms'...I want to avoid baffling people with abbreviations and mathematical conundrums. I would welcome your help enormously.

    3. What is the serial number of Worsley's sextant? I've been baffled for years and I can't deduce that from photographs alone. Every time try to see Worsley's sextant, its removed from display or overseas - very annoying!

    4. With regards Worsley's sextant, the one used on the James Caird, there was only one sextant aboard the boat according to the equipment list recorded in Shackleton's personal account: South. In combination with Worsley's personal account, we know that the sextant used was loaned to Worsley by Hudson, it was manufactured Heath & Co without a doubt.

    5. The sextant is not on display at Dulwich College, only the James Caird can be found on display there alongside two Nansen style seldges, and a Burberry windproof suit worn by Kenneth Brannagh in the film 'Shackleton'.

    6. The photograph of Worsley using a sextant was taken aboard Quest, I doubt it would be the sextant used during the voyage of the James Caird. It would be too precious in my personal opinion to be used again...perhaps I am wrong. It strikes me that Worsley would probably use a new sextant provided by the expedition.

    7. With regard switching instruments during a critical voyage, it would be bad practice to switch between instruments - the errors could amount considerably in estimating a position. If anything, both sextants would be used at the same time by Worsley and Shackleton in order to do a comparison - which was common practice for hundred of years however, there is no mention of this taking place during the voyage of the James Caird so I strongly believe only one sextant was taken on the journey. These were very smart men, with great seamanship ability...they' would risk switching instruments, unless one was catastrophically damaged, or lost.

    I would be delighted to continue discussing this interesting topic, can I invite you to join my website Forum. Likewise, I would be delighted to continue contributing through this site.

    Regards to all your readers.

    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

    View and reply to this message: http://fer3.com/arc/m2.aspx?i=126772

    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