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I watched the National Geographic documentary on Endurance. Although the original photographs and colourized movies from Shackleton's Imperial Trans-Antarctic Expedition were engrossing and very well done, coverage of the Endurance22 search was tedious and probably deserves its 1.5 star rating. I had hoped that to get some insight into why, despite having solid evidence and analyses to the contrary, the Endurance22 team seemed to have clung to the unjustified belief that the wreck would be found near the position given by Captain Frank Worsley in the log. Consequently they wasted a great deal of time and effort in the first stages of the search in that area. In an opening sequence Dan Snow, historian and broadcaster, explains "We are near the latitude and longitude given by Worsley, the captain of Endurance, as the place where he estimates Endurance sank". This position is 69°39'30"S 52°26'30"W but an examination of how it was obtained clearly shows that it is not anywhere near where the wreck was to be found.

BACKGROUND

A collaboration of Navlisters that initially included Brad Morris and the late George Huxtable, Lars Bergman and myself had made a comprehensive study of Captain Frank Worsley's original logbooks in order to understand what methods he had used to navigate the James Caird from Elephant Island to South Georgia Island. Lars and I also examined the navigational methods Worsley had resorted to while Endurance was trapped in the sea ice during the winter of 1915. In particular the latter contained a detailed study of the occultation timings that Worsley and expedition physicist Reginald James had made to rate their chronometers and hence determine their longitude. Our results were ultimately published in 2018 edition of Records of the Canterbury Museum

Bergman, Huxtable, Morris and Stuart Navigation of the James Caird on the Shackleton Expedition. Records of the Canterbury Museum 32 (2018) 23–66.
Bergman and Stuart Navigation of the Shackleton Expedition on the Weddell Sea Pack Ice. Records of the Canterbury Museum 32 (2018) 67–98.

In April 2018 I listened to a BBC interview of Prof. Julian Dowdeswell of the Scott Polar Research Institute at Cambridge University. He was to lead The Weddell Sea Expedition 2019 that would carry out a program of science centred in the waters around Larsen C Ice Shelf and in addition search for the wreck of Endurance. This part of the expedition was to be directed by Mensun Bound. In the interview Dowdeswell commented that he believed they knew the position of Endurance to within about half a mile. This seemed a bit optimistic to me but, since we had access to Worsley's entire original logbook, it was something Lars Bergman and I could investigate. This we did and published our conclusions in Bergman and Stuart, On the Location of Shackleton’s Vessel Endurance. Journal of Navigation 72 (2019) 257–268.

Key findings from that paper were:

1) Endurance sank around 5pm on 21 November, 1915 but no sextant sights for position could be made on that day or for the 2 days prior.

2) The position given for the sinking was obtained by applying a 1.2 nautical mile (NM) south east offset to the location of Shackleton's Ocean Camp as it was at noon on the 22 November, a full 19 hours after the sinking.

3) Accounts from the crew's diaries indicate that, in the intervening 19 hour period, the wind was blowing predominantly from the south. This would cause the ice sheet to drift north from the sinking location. Extrapolating back from the ongoing northerly drift measured on 22 and 23 November the location of the wreck could be up 4.5 NM from the

4) Worsley made an arithmetic error in the reduction of his noon sight. When corrected this introduces an additional shift in true position of 1 NM to the south.

5) Uncertainties in longitude were a bit more difficult to determine but it appeared that Worsley had a tendency to underestimate how slow his chronometer was running. This would push the true position to the west of that given in the log.

The inescapable conclusion here is that it has been well-known for a long time that the position of the wreck would be south of the position Worsley recorded in the logbook by up to 5.5NM.

In September 2018 I sent Prof. Dowdeswell a copy of our paper. He replied thanking me and said that they were  already aware of it.

The expedition contracted Frank Reed to conduct an independent review of our work.

The Weddell Sea Expedition published an account of the search in a paper available at https://www.cambridge.org/core/journals/antarctic-science/article/seafloor-and-seaice-conditions-in-the-western-weddell-sea-antarctica-around-the-wreck-of-sir-ernest-shackletons-endurance/0D4511F2859986967E6F53490F27F0D3
that cited our paper. They had planned to search a 20 NM × 20 NM area centred on a position they correctly called the "location of Ocean Camp" and notably not Worsley's position for the sinking. Mensun Bound was not a co-author on that paper. Unfortunately the search was unsuccessful as the Autonomous Underwater Vehicle (AUW) being used was irretrievably lost before it could return any data. Had they completed the search as planned the Endurance would have been found.

Some time afterwards we were contacted by David Mearns of Blue Water Recoveries Ltd. David is a professional wreck hunter who has spent years scouring the archives for clues to the location of Endurance. He had found a paper which showed that, on his return to England, expedition physicist Reginald James worked with Greenwich Observatory astronomer, A. D. Crommelin, to reanalyze the occultation timings using the Moon's observed position rather than those given in tables in the Nautical Almanac which were known to be of limited accuracy. Their corrections shifted the true position of the wreck to the east of that in the logbook. We reanalyzed the occultation timings with modern JPL models of the Moon's motion and modern star positions and found a somewhat larger shift and an overall much better fit to the observations. This additional effect pushes the true position to the east and counteracts the westerly offset mentioned above.

For more details on all of this see the YouTube video of my talk to the Royal Institute of Navigation.

We submitted our updated conclusions to the Journal of Navigation on 29 July 2021 hoping and expecting that it would appear in print before the new search expedition, Endurance22, set out. Unfortunately the Journal of Navigation now seems to have a review process that takes an exceedingly long time compared to other professional journals and it still had not appeared in February 2022. Wanting to ensure that Endurance22 was in possession of the best available data we made the paper available as a preprint on Navlist. This paper concluded that the wreck would be to the east of the position given in the log by, depending on the strength of the easterly wind, by up to 3.5NM.

ENDURANCE22

We know that Endurance22 got the paper as there were some indications that they adjusted their planned search box to the east and Frank Reed was again contracted to review our work.

Navlisters could follow to search's progress thanks to the excellent charts produced by Matus Tejiscak. The search strategy is very hard to understand but may have been partly constrained by the sea ice conditions. They spent the first part of the permitted search period in the vicinity of the Worsley's log position even apparently searching to the north where the wreck couldn't possibly be. This was followed by a series wide area sweeps far to the east where again the wreck couldn't reasonably be. Only on 4 March, in the last few days of their extended search permit, did they start a west to east transect about 5NM south the log position. The wreck of Endurance was found at on 5 March 2022 at 68°44'21"S 52°19'47"W. This is 4.9NM south and 2.4NM east of the position given in the log.

Watching the National Geographic documentary I got no insight into why they adopted the strange search pattern they did nor what motivated their final successful transect to the south. Indeed I came away with the impression that the search was based more on starry-eyed awe for Worsley's legendary but mysterious navigational skills than by any real understanding of the meaning of the numbers in the logbook or the caveats surrounding them. When a potential target was found just 400 metres north of the log position it generated congratulations and hugs all round along with declarations of what an amazing navigator Worsley was. John Shears, expedition leader, exclaims, "I can't believe it. Worsley really was an ace!". When it was found that what was seen was at best just a small debris field and not the wreck itself Mensun Bound ruefully confides "I could hear Shackleton himself laughing his head off there somewhere in the background, 'cause we made fools of ourselves".

Robin Stuart