The real reasons Endurance sank — study finds Shackleton knew of ship’s shortcomings

Sir Ernest Shackleton’s ship, Endurance, was crushed by Antarctic sea ice and sank in November 1915. Emblematic of the heroic age of Antarctic exploration, it is widely considered the strongest polar ship of its time, albeit with a fatal flaw — a weakness in the rudder that caused the ship to sink. 

Now, a world-first study incorporating both technical analysis and research into diaries and correspondence sheds new light on the expedition and the man himself. Not only did the ship have structural weaknesses that made it notably less robust than other early polar vessels but also, remarkably, the famed explorer was well aware of them before he set sail. 

‘Even simple structural analysis shows that the ship was not designed for the compressive pack ice conditions that eventually sank it,’ says Jukka Tuhkuri, a professor of solid mechanics at Aalto University, and one of the world’s foremost ice researchers. ‘The danger of moving ice and compressive loads — and how to design a ship for such conditions — was well understood before the ship sailed south. So we really have to wonder why Shackleton chose a vessel that was not strengthened for compressive ice.’ 

A polar explorer himself, Tuhkuri was one of 15 scientists who were invited to join the Endurance22 mission, the team that discovered the wreck in 2022. Surprised that fundamental structural analysis of the vessel had never been conducted, the wreck’s discovery fuelled his own desire to reveal the scientific truths behind the legend. 

‘Endurance clearly had several structural deficiencies compared with other early Antarctic ships,’ he explains. ‘The deck beams and frames were weaker, the machine compartment was longer, leading to serious weakening in a significant part of the hull, plus there were no diagonal beams to strengthen the hull. Not only does this challenge the romantic narrative that it was the strongest polar ship of its time, but it also belies the simplistic idea that the rudder was the ship’s Achilles’ heel.’ 

After analysing Shackleton's diaries, personal correspondence, and other communications from the crew, what is less clear to the researcher is why the famed explorer chose to sail into the dangerous Antarctic ice pack aboard Endurance.

‘Shackleton knew about this. Before he set off he lamented the ship’s weaknesses in a letter to his wife, saying he’d exchange Endurance for his previous ship any day. In fact, he had recommended diagonal beams for another polar ship when visiting a Norwegian shipyard. That same ship got stuck in compression ice for months and survived it,’ says Tuhkuri. 

So was Endurance simply “ill-fated”, or were poor decisions the real root of the ship’s demise?

Tuhkuri doesn’t want to make that judgment. He says the study doesn’t seek to detract from the heroic achievements of Shackleton and the men who travelled with him to the Weddell Sea more than hundred years ago. But he does hope it will add a new perspective to the way we look at Endurance.

‘We can speculate about financial pressures or time constraints, but the truth is we may never know why Shackleton made the choices that he made. At least now we have more concrete findings to flesh out the stories,’ he concludes.

The study was published on October 6th in the prestigious Polar Record journal.

Professor Jukka Tuhkuri researches ice mechanics and arctic marine technology at Aalto University in Finland. His laboratory experiments are conducted in the Aalto Ice and Wave Tank, the world’s only large-scale ice and wave research facility. His research into changing ice conditions due to climate change has taken him to the Arctic and Antarctic and he is author of Jään voima (in Finnish) — his account of the sinking and discovery of Endurance.