100 years ago, the “Ghost Ship” sails disconcerted Einstein – now they make a comeback

On the rough and frozen waters of the North Sea in 1925, an unusual ship has made a way in Danzig, Poland, Leith, Scotland, marking a first in maritime history. This first trip was historic not for its distance but for the ingenuity of the ship: its simple design even impressed Albert Einstein, who then wrote a test dedicated to his meaning.

“Bare from all sails, masts and rigs,” wrote GB Seybold, reporting for Popular science,, The 177 -feet long steel schooner was propelled by nothing more than “two strange cylinders, resembling giant steps of smoke. But no smoke spilled and no engine noise was heard. Like a ghost ship, it mysteriously moved into water without a means of propulsion. ”

Several months later, on Charles River in Boston, two officers of the American Navy, a MIT student, launched their own modified version of the same strange ship. “This American boat,” wrote Popular science In September 1925, “was the first real demonstration in this country of the way a rotating metal tower can replace the sails on canvas.”

In the late 1920s, orders for strange “strange rotor ships” began to rise. These hybrid ships – combining oil or coal engines with large rotation cylinders – processes to halve fuel consumption. Such savings were not only theoretical. In 1926, the first Rotor ship, the Buckauwho had made the Trek of the North Sea, was rebuilt as a hybrid and renamed the Baden-hobby. He sailed from Germany to New York via South America, a journey of 6,200 nabin miles which used only 12 tonnes of oil compared to the 45 tonnes that it would have required without rotors. A new, more efficient shipping age seemed imminent.

But just as the momentum has gathered for the new Wind-Ship technology, the stock market crashed. The great depression followed. Fuel prices have plunged. The economic advantages of rotor sails have disappeared almost overnight, and with it promising technology. A century later, however, when the maritime transport industry confronts the volatile costs of fuel and climate change, Rotor sails are making a return.

The math teacher who invented a new type of ship’s sail

The idea of ​​Rotor Sails belonged to Anton Flettner, professor of mathematics and self -taught engineer, who patented his new invention in 1922. His conception was based on a well -known aerodynamic principle, described for the first time in the 19th century by the German physicist Gustav Magnus.

Baseball fans know the effect of Magnus well: he explains how a curve ball folds. When a rotating object moves in the air or any liquid, its rotation modifies the air pressure – moving with the rotation of the flows faster and the air moving against the rotation flows more slowly. The result creates a force that pushes the object laterally. This is how Coco Gauff hits a shot with Topspin or Tarik Skubal launches a curve ball. The airplane wings also get an elevator of the same principle.

Flettner understood that if he could keep a vertical cylinder turning on the bridge of a ship, it would exploit the Magnus effect, catching the wind and pushing the ship forward or backwards, depending on the direction of the rotation. Unlike conventional sails, which stand out from the wind, making them capsizing, the Magnus effect pushes the sails of the rotor in the opposite direction, which forces them to look into the wind, making them surprisingly stable in stormy weather. But unlike conventional sails, which require no power other than wind, rotor sails require something to keep them in rotation.

Rotor Sils’s Rise and collapse

In Boston, the Navy officers Joseph Kiernan and WW Hastings, put the invention and theory of Flettner to the test. When they ran their rotor ship made up for a yacht in the Charles river in 1925, losing by a small margin, the Time magazine was amazed by the ship’s mechanics: “A 35-foot 35-foot cup was moving regularly, not making gas smoke, a range of the size of the terrace. A smokeless battery which increased in the middle of a cylinder three and a half feet in diameter and nine and a half feet high. The slight “put-step” was the sound of the gas engine at a and a half Kiernan and Hastings used to keep their cylinder turning and direct the ship.

When the bottom fell from the nascent Rotor ship industry during the Great Depression, Flettner left. At the time, he was already a prolific inventor. He had previously invented the adjustable fitting system, or Servo tabs, still used by planes and ships today. A small articulated surface, the Flettner servo tabs use the power of the air or water passage to move a much greater control surface with a minimum of effort, mainly acting as a “powerful direction”. In the 1930s, Flettner adapted its rotor conception to helicopters, developing intermesting rotorcrafts (rotor sets which were turning in opposite directions for stability) which influenced subsequent conceptions.

In 1961, Flettner died. Despite a prolific life of innovation in the aeronautical, marine, automobile and energy industries, Flettner – who had started as a math teacher at high school and became director general of the Institute for the aerodynamic and hydroelectric dynamics in Amsterdam, as well as as a consultant for the American Naval Research Office after the Second World War – adopted.

The modern return of the invention of the old

Today, the maritime transport industry carries more than 80% of world goods, but this generates around three percent of global greenhouse gas emissions. In 2023, the international maritime organization set an ambitious target of GES Net-Zero emissions by 2030 for the maritime industry. The ports began to tighten the emission rules, put pressure on ship owners to find and implement greener propulsion systems. With the volatile oil prices and the urgency to reduce emissions, the Rotors of Flettner have returned.

Norsepower of Finland, founded in 2012, equipped 22 Rotor sails ships in June 2025 with 17 other under contracts. Although it is a tiny fraction of the more than 100,000 cargos with the Earth oceans, the economy – up to 25% or more savings in fuel and GHG emissions – are convincing.

It remains to be seen if they will remain convincing enough for a generalized adoption. But a century after Einstein was amazed at their simple design, the Rotors of Flettner could finally reproduce.