On Oct. 27, 1915, after being caught and crushed by packed ice for nine months in the Weddell Sea off Antarctica, Ernest Shackleton and his crew abandoned the Endurance and their quest to traverse the frozen continent by land. The doomed ship drifted atop the ice for three more weeks before finally sinking.

For over a century, experts have put the blame for the ship’s demise on an ice floe overwhelming the rudder and creating a large gash in the vessel. But a study released Monday in the journal Polar Record contends that the ship, not the ice, was to blame. The Endurance was ill equipped for its mission, a flaw that Shackleton was aware of long before he launched to Antarctica.

Jukka Tuhkuri, an ice researcher and naval architect and author of the new study, was aboard Endurance22 with the team that discovered the wreck in 2022. As a side project, he began analyzing diaries, personal correspondences and the ship’s wreckage to find out why the Endurance sank.

A year and a half later he was staring at images of what had been described as the strongest wooden ship ever built in the archives of the Royal Geological Society in London. A hypothesis came to him.

“It’s not the ice, it’s the ship,” Dr. Tuhkuri said.

He noticed that the hull of the Endurance lacked the beams that would have given it enough brawn to endure an onslaught of crushing ice. As a result, the rudder, stern post and part of the keel were torn apart, causing the ship to fill rapidly with water.

While Shackleton wrote in his book “South: A Memoir of the Endurance Voyage” that it was insurmountable ice floes that doomed his ship, the study suggests that he knew otherwise. He wrote to his wife, Emily Shackleton, that “this ship is not as strong as the Nimrod constructionally,” referring to the wooden vessel Shackleton took on his 1908 Antarctica expedition.

Endurance, a touring ship built for hunting polar bears and walruses in the Arctic, was “designed to work at the edge of the pack ice but not to be frozen in,” said Walter Ansel, the senior shipwright at Mystic Seaport Museum, in Mystic, Conn., who was not involved in the study.

Not only was Shackleton aware of Endurance’s shortcomings, but he also had the expertise on how to fix them. He had helped the German polar explorer Wilhelm Filchner equip his ship Deutschland with the same structural beams that Endurance lacked. Later, in 1912, Deutschland drifted in the ice-packed Antarctic waters for eight months but survived.

The paper notes five ice compression events taken from the diaries of crew members, building up to a culminating event on Oct. 17. One crew member, Reginald James, wrote that “the pressure was mostly along the region of the engine room where there are no beams of any strength.” Capt. Frank Worsley described the engine room as “the weakest part of the ship.” Both entries, dated to Oct. 17, describe a ship being crushed by ice because of its structural inadequacies.

The American whaling fleet had repeatedly run into similar catastrophes. In 1876, 12 inadequately reinforced ships were lost as a result of compressive ice near Alaska, Mr. Ansel said.

Michael Bravo, a professor at the Scott Polar Research Institute at the University of Cambridge, who was not involved in the study, said many polar exploration ships were not suited for their journeys. Such vessels were seldom readily available. “Most of them were purchased second hand and adapted as time and money permitted,” Dr. Bravo said.

Indeed, this could have been true of Endurance, suggests Michael Smith, author of the book “Shackleton: By Endurance We Conquer,” who was not involved in the new study. Shackleton may have known that the ship wasn’t ideal for the voyage. But he was restless at home, and struggling with financial debt and a failing marriage.

“The scale of this expedition is truly daunting, but he needed something to get his teeth into and he wanted to get away,” Mr. Smith said. He added that Shackleton was competing with other explorers to conquer the Antarctic.

Still, Mr. Smith doubts this will change our view of Shackleton. Historians knew already that he was a man who took chances and made big calls under pressure. The grave risks of these missions were known to the explorers.

“To be a polar explorer a century ago was an act of faith in itself,” Mr. Smith said.