A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Robin Stuart
Date: 2018 Dec 19, 13:31 -0800
I trust that people notice that there are actually 2 papers that relate to the Shackleton Expedition in this year’s edition of the Records of the Canterbury Museum. The second one that I attach here for the Navlist Archives. This paper details with the non-standard navigation methods employed while they were trapped in and camped on the ice floe. Principally these are ex-meridian sights of stars and lunar occultations for rating the chronometers.
Lars Bergman informs me that his first email exchange with George Huxtable was in March 2009 on the subject of traverse tables. I was a relative latecomer but am very happy to have seen it to completion. Records of the Canterbury Museum is an annual publication and the James Caird paper had been accepted for publication by October 2017. At that time I visited the Museum and was given an hour to inspect and photograph the log and related materials. It was then that I came across Worsley’s signed sketch map of King Haakon Bay (Figure 5), decided it needed to be seen and that our paper would be the perfect vehicle for that purpose. So we requested a delay until the 2018 edition. In hindsight that turned out to be a good decision as it also allowed time to extend the transcript all the way to the end of the log entries. Perhaps more importantly, in the course of preparing our other paper, Lars noticed that one on the loose leaf pages contained a table of anticipated chronometer errors that completely changed our interpretation of the cryptic phrase “allow 1minute+4sec more”. This was crucial in correctly understanding the adjustments Worsley had made in rating the chronometer just prior to setting off for South Georgia.
I hear it stated from time to time that Worsley was just doing Parallel Sailing. This is complete and total BS and let it never be uttered again! Worsley was heading for a point 27 miles west of Wallis Island. From our Figure 6 it is very clear that he was sailing upwind of but roughly parallel to the rhumbline from Elephant Island to that point until instructed by Shackleton to head for the south coast of South Georgia.
Certaine Errors in Navigation
For me one of the more surprising bi-products of this work was the identification of some very longstanding errors.
First it should be pointed out that there are occasional simple errors to be found in the log but that in that crucial period 14 day of the voyage of the James Caird there are none!
Our investigations into the sources Worsley used to determine his longitude on Elephant Island lead to some mislabelled features being identified on Chart 29104 and resulted in two Notices to Mariners being issued as described here
In the second paper, Lars and I deciphered Raper’s Method for the reduction of lunar occultations. It was published in 1841 and in true navigational style it describes the required steps in terms same name and contrary name-ology. But Raper was just a bit imprecise and and his words were misinterpreted and incorrectly rephrased in the Royal Geographical Society’s Hints to Travellers. Reeves who was a later editor of Hints to Travellers even published a derivation of Raper’s method in his book Trigonometry: Plane and Spherical but did not notice or correct error. Reeve’s also extended the examples in Hints to Travellers from 4-figure to 5-figure logarithms but never bothered or was not able to extend the various constants that go into the calculation to 5 figures. He simply tacked a zero on the end. All of this seems just a bit shoddy.
This now incorrect methodology was made its way into Close’s Textbook of Topographical and Geographical Surveying which Worsley used. Fortunately the problem only arises when latitude and the star’s declination are contrary name which fortunately will never really happens in practice in the polar regions.