The spectacular images went around the world: more than 100 years after it sank, the famous research vessel "Endurance" was found at the bottom of the Weddell Sea at a depth of 3008 metres in 2022. The images show a remarkably well-preserved ship with the name "Endurance" still visible on the stern. They barely give an idea of the massive forces with which icebergs and pack ice beset her for months and how Shackleton and his crew fought to save her. The fight was in vain. Eleven months after the pack ice had taken the almost 44-metre-long schooner barque in its grip, it sank on 21 November 1915.
Shackleton and his crew, who had set out to be the first people to cross Antarctica, had to make their way north on foot, with the dinghies in tow. The adventure of their successful rescue gave polar explorer Ernest Shackleton hero status.
For a long time, the main cause of the sinking was thought to be the rudder breaking off. However, Finnish engineer Jukka Tuhkuri from Aalto University has now disproved this theory. Based on diaries from the expedition, Shackleton's letters and structural analysis of the "Endurance" he shows: It was not the loss of the rudder, but the general pressure of the ice that caused the ship to sink. He also comes to the conclusion that Shackleton deliberately chose an unsuitable ship for the dangerous journey.
Unsuitable ship despite better alternatives
When the "Endurance" - then still known as the "Polaris" - was launched on 17 December 1912 in Sandefjord, Norway, its purpose was clear: to take tourists to the edge of the Arctic in the Arctic summer, to the Greenland Sea and to Spitsbergen. With extra-thick planks and frames, she is ideally equipped for the conditions at the edge of the pack ice. Thanks to her comparatively slim and straight hull shape, she sails well and can sail through ice floes. However, the schooner barque was never intended to take on this task: Her owner is broke and sells her to the adventurer Shackleton for an Antarctic expedition into the pack ice. "But the conditions at the edge of the pack ice in the Arctic are very different from those deep inside the pack ice in the Antarctic," writes Tuhkuri. "At the ice edge, the ships usually have to contend with collisions with ice floes. The Endurance was designed for these kinds of ice conditions, and its planking and frames are thick and strong enough for the task."
The thickness of the planking and the frames is one thing, says the Finnish engineer, but: "In pack ice conditions, where the pressure of the ice has to be taken into account, the deck beams are of crucial importance. They are what hold the two sides of the ship apart and maintain the shape of the ship. If they are not strong enough, a ship will be crushed by the pressurised ice."
It is here in particular, but also in other design details, that the "Endurance" differs from other expedition ships of its time (see below). Tuhkuri's research has shown that Shackleton must have known that the "Endurance" was unsuitable. In 1910, the German Wilhelm Filchner took over a boat built at the Framnæs shipyard in Sandefjord for whaling and sealing in the Arctic and initially christened "Bjørn".
Filchner plans the second German South Polar expedition. He names the ship "Deutschland" and has it modified for the new purpose at the Norwegian shipyard.
He was advised by Ernest Shackleton, of all people, who visited the shipyard in early 1911. A few years earlier, the explorer himself had already toyed with the idea of buying the "Bjørn" for his first Antarctic expedition from 1907 to 1909, but a chronic lack of cash for his endeavours was a recurring theme in the adventurer's life, so he had undertaken the journey on the less expensive "Nimrod".
Based on his experience in the ice, he now advises Filchner to reinforce the hull of the "Deutschland". Diagonal support beams are used and the deck beam span is reduced, making the structure significantly more robust against compressive ice loads; according to Tuhkuri's calculations, the "Deutschland" was able to withstand one and a half times more ice pressure than the "Endurance" later on - which was being built in the same shipyard at the very time that the "Deutschland" was being modified.
The measure proves successful. Filchner reaches the Weddell Sea and is trapped by the pack ice. The "Deutschland" drifts with the ice in slow motion for eight months, but is finally freed unscathed - two years before Shackleton is due to set off with the "Endurance".
There were also other proven models for truly stable, wooden expedition ships at the time the schooner barque was launched. The most famous of these is probably the "Fram", developed by Fridtjof Nansen and Colin Archer especially for the pack ice. It was launched in 1893 and was first used by Nansen in his attempt to reach the North Pole from 1893 to 1896 by drifting with the ice, and then by Roald Amundsen on his legendary Antarctic expedition from 1910 to 1912.
The successes of the "Fram", the "Deutschland" and other ships had shown how a ship must be designed to withstand the enormous demands of the Antarctic, and Shackleton is aware of this. As well as the fact that with the "Endurance" he may have a ship with an excellent reputation, but certainly not the one with the best suitability. So he writes to his wife Emily from the road: "This ship is not as strong as the "Nimrod" in terms of construction, I saw that in her behaviour when she pressed against the dock wall here in a storm, but there is nothing to be afraid of, because I think she will get through the ice just fine. Still, I'd swap her for the old 'Nimrod' any day."
Why Shackleton still went on an expedition with the "Endurance"
Nevertheless, he sails with her towards the South Pole. And he has good reasons for doing so. For a long time, Ernest Shackleton has been something of a dowdy child among respected polar explorers. The man of Irish origin was not a member of the honourable Royal Navy; he had only spent a few years in the merchant navy. Nevertheless, the highly respected Sir Robert Scott took him on board the "Discovery" in 1902 for a South Pole expedition. The golden age of Antarctic exploration had begun, the race to be the first to reach the pole. Scott, the explorer and doctor Edward Wilson and Shackleton set off on foot from the frozen "Discovery" in dog sledges towards the Pole. But Shackleton falls ill with scurvy and has to travel temporarily on a dog sled. Back on board, he quickly feels better after eating plenty of fresh seal meat, but Scott declares him unfit for service and sends him home at the first opportunity. Shackleton is in his late 20s, full of the spirit of discovery, but broke and inglorious. During this time, he may have developed a certain ambition to overtake Scott in the race to the Pole. To achieve this, he organised his own expedition. Between 1907 and 1909, he travelled closer to the South Pole in the "Nimrod" than anyone before him. This brought him a certain degree of fame, but also doubts.
He travelled the country to pay off the mountain of debts that his expedition had brought him with lectures and publications. At the same time, a debate about his credibility was sparked by the Royal Geographic Society. Its distinguished member Sir Clements Markham wrote to the current president in September 1909: "Shackleton's failure to reach the South Pole, although it could have been done by someone else, is really a matter of calculation and it annoys me. (...) I cannot accept the latitudes."
Markham doubts that Shackleton and his men could have gone "pulling the sledge and half-fed, in a straight line fourteen miles a day, up a steep slope 9,000 feet above the sea, for twenty days". The "other" whom he believes to be the only one capable of winning the race around the Pole is his protégé, Sir Robert Scott.
The seeds of doubt about Shackleton's achievement are sown. Scott hurriedly set about claiming the rights to the next expedition for himself. The idea that the two best expedition leaders in Great Britain would be most likely to succeed if they tackled the task together no longer occurred to anyone at this point. The rivalry was too great. It would not end until 1913 with the news of the death of Scott and his companions, almost a year after they had died in the perpetual ice while attempting to reach the South Pole - and also a year after Roald Amundsen had reached the Pole first from his "Fram" and outdistanced his companions.
Shackleton does not let this get him down and develops his next major project. In a letter in The Times in December 1913, he announced an expedition for the following year in which he intended to cross the continent from sea to sea. Generous support from the Royal Geographic Society is not to be expected; old doubts speak against this, as does Shackleton's refusal to subordinate the expedition solely to scientific benefit.
He calls it the "Imperial Trans-Antarctic Expedition" - a British mission designed to generate patriotic feeling among the masses beyond the scientific elite and raise money for his endeavour. He raises just enough to buy the "Endurance" and the necessary equipment. There is also no time to think about an elaborate modification: it is 1914 and England is mobilising. So the "Endurance" sets sail from Plymouth on 8 August and travels to Antarctica via Argentina and South Georgia.
Shackleton describes his personal motivations in a letter to his wife: "I am only as good as an explorer and nothing more; I am hard and damned stubborn when I want something: altogether a generally unpleasant character. I love the struggle, and when things are easy, I hate it."
Sinking in the ice
At that moment, he probably doesn't realise just how simple things are about to become. He concludes: "Now that I'm working on my own work, I'll be better and more peaceful, and I don't think I'll ever go on another long expedition; I'll be too old."
On 18 January 1915, the ship is stuck in the ice in the Weddell Sea. In slow motion, it drifts 570 miles to the north-west in ten months. The crew tried again and again to break up the ice around the ship, to steer it, to save her. "The behaviour of our ship in the ice," writes navigator Frank Worsley in his diary, "has been excellent. Since we have been shut in, its steadfastness and endurance have always seemed beyond imagination. It would be sad if such a brave little ship were ultimately crushed by the merciless, slowly suffocating grip of the Weddell Pack, after ten months of the boldest and bravest fight ever waged by a ship."
In October, however, the melting ice in all its enormous forms - ice floes here, an iceberg there - turned its grip into one of destruction. Shackleton describes the situation in his book "South": "The central part of the ship was pressed downwards, the ship tilted more and more to port and starboard until the Endurance settled on the ice floe and remained there, crushed between ice floes and icebergs. The joints of the planks opened (...), and at the same time we could see the ship bending like an arch under titanic pressure. Almost like a living being, it resisted the forces."
The crew had to disembark and watch from their camp on an ice floe as their ship slowly fell victim to the merciless ice. On 21 November, the "Endurance" finally sinks into the ice.
What follows is one of the most astonishing rescue operations in history. The 28 men fight their way to the uninhabited Elephant Island, first on foot and later with dinghies. From there, Shackleton and five of his men sailed 800 icy, stormy nautical miles in an open boat to South Georgia, crossed the mountainous island on foot and reached a whaling station.
After several failed attempts, he was finally able to rescue the men left behind on Elephant Island in August 1916. All of them survived. It is this almost superhuman feat that makes Shackleton a British national hero. On the way to his fourth polar expedition, the expedition leader and polar explorer died of a heart attack in Grytviken on South Georgia in 1922 at the age of 47.
What sets the "Endurance" apart from other expedition ships
Tuhkuri divides the polar ships of the late 19th and early 20th centuries into three structural categories: Wooden ships following the tradition of whalers, wooden expedition ships built for pack ice conditions, and steel icebreakers and other icebreaking vessels. The "Endurance" is an example of the first type. It is one of the last polar ships - if not the last - to be built in the tradition of wooden whalers and sealers, designed to operate at the ice edge because that is where whales and seals can be found, but not for the permanent pressure of being trapped in pack ice.
The shape and size of the "Fram", on the other hand, is such that it is lifted by the ice that presses against its sides. This is ensured by an optimised, more oval hull shape and a short waterline length. Poor sailing characteristics, but excellent ice-capability. Retractable rudders and propellers also contribute to her safety in ice, but above all diagonal supports and additional stanchions to reinforce the hulls.
The "Endurance" does not have these additional reinforcements. Its large, open engine room also makes it particularly vulnerable. The 350 hp engine and steam boiler take up so much space that there is hardly any room for a stabilising tween deck. Lengthways, there is a bulkhead in front of the engine room and another behind it, but vertically, the open space is only defined by the main deck and the keel. This means that the entire pressure load is borne by the main deck at this point, while the stabilising deck beams lose strength due to their span.
Wreck found after more than a century
More than 100 years after its sinking, the wreck of the "Endurance" is discovered in March 2022 by an international team of researchers as part of the "Endurance22" expedition. The search is based on the detailed diary entries of Captain Frank Worsley. Hybrid autonomous underwater vehicles are used to search the seabed in a grid pattern until the wreck is found about four miles south of the position noted by Worsley. The images show a remarkably well-preserved ship, with the name "Endurance" still visible on the stern. The extensive damage, particularly to the rudder, keel and side planks, that caused her sinking is barely visible in this position. And they will always remain hidden, because according to the Antarctic Treaty, the wreck is considered a "cultural property of mankind" and may not be salvaged.
The chronicle of the Endurance expedition
Despite the decision regarding the choice of boat, which is questionable from today's perspective, the story of the "Endurance" expedition remains an extraordinary chapter in polar research.
17 December 1912: The schooner barque "Polaris", later renamed "Endurance", is launched in Sandefjord, Norway
8 August 1914: The "Endurance" departs from Plymouth and travels to Antarctica via Argentina and South Georgia. Her destination: Vahsel Bay
18 January 1915: The "Endurance" is stuck in the ice in the Weddell Sea. She drifts 570 miles to the north-west in nine months
27 October 1915: The melting ice crushes the ship and it springs a leak. The crew disembark and camp nearby
21 November 1915: The "Endurance" disappears under the ice and sinks. Captain Frank Worsley notes her last position
23 December 1915: The crew sets off on foot on the arduous journey north, the dinghies in tow
29 December 1915: The ice becomes insurmountable. The crew holds out in tents for three months on a drifting ice floe
9 April 1916: The ice floe breaks. In open boats, the men row and sail to Elephant Island in seven days
24 April 1916: Shackleton and five of his men set off in the dinghy "James Caird" to fetch help in South Georgia
10 May 1916: The "James Caird" reaches South Georgia. Shackleton walks across the island to the Husvik whaling station
30 August 1916: After three failed attempts, Shackleton succeeds in rescuing the 22 men on Elephant Island. All live
8 March 2022: The research team of the "Endurance22" expedition finds the wreck at a depth of 3008 metres in the Weddell Sea
