On a cargo ship packed with 8,700 shipping containers, there isn’t much room for anything else. But in a new test aboard one of its vessels, Maersk is making an exception for a giant rotor sail—a spinning cylinder 10 to 12 stories tall that harnesses wind to help reduce fuel use.
The test comes as shipping fuel costs continue to soar. In some areas, the price has risen as much as 76% since the Iran war started. The tech, made by a U.K.-based company called Anemoi, is one way to help blunt future price spikes while also cutting carbon emissions for one of the world’s most polluting industries. It’s also an example of how the industry is increasingly making use of wind power.
The 115-foot-tall rotor sail works much like an aircraft wing, which generates lift as air moves faster over the top of a wing than underneath.
“Our rotor sails work on the same basic principle of creating a pressure difference, but instead of a wing, we use a tall spinning cylinder,” says Anemoi CEO Clare Urmston. “As the cylinder spins, it speeds the airflow on one side and slows it down on the other. This creates low pressure on one side and high pressure on the other, producing the force that pushes the ship forward.”
In some cases, each sail can reduce around 1 ton of fuel use per day, but depending on wind conditions, that can jump to as much as a 20-ton reduction. Each ton of fuel saved also saves the equivalent of 3 tons of CO2 emissions. It’s not turning a cargo ship into a sailing vessel—a ship like Maersk’s can use 100 tons of fuel in a day. (Some other companies, like Vela, are building cargo ships that do run entirely or almost entirely on wind.)
But the fuel savings are significant, and could translate into saving hundreds of thousands of dollars for a vessel in a year. The payback period for one of the devices is typically five years, but it can be faster for ships operating in Europe under stricter regulations for shipping emissions.
In the past, Anemoi has worked with other types of vessels, like bulk carriers transporting raw materials. But the new installation with Maersk is its first on a container ship. In theory, the wind flow around the shipping containers may actually help the sail perform better.
“It’s the first of its type,” Urmston says. “So we’re really excited to be part of this pioneering study and see how that works. It could be a big change for the container ship market going forward if successful.”
The rotor sail will be installed on the Maersk ship in mid-2027; the company will then track performance as the ship goes on a regular route across the Atlantic. Though the vessel uses standard shipping fuel now, the technology could also help as ships transition to lower-carbon fuels in the future.
“Wind is really attractive because it doesn’t require predicting which fuel will be burnt in the future, so it’s complementary to all alternative fuels,” Urmston says. Because alternative fuels are more expensive right now, she adds, there’s even more of a case for adding wind to help.