Mechanical rotor sails harness the renewable power of the wind to propel ships

Anemoi Rotor Sails Wind Energy
The spinning Rotor Sails use the Magnus Effect to generate a thrust force which provides auxiliary propulsion to the vessel. Images © Anemoi Marine

Singapore-based dry bulk owner Berge Bulk has signed a deal with Anemoi Marine Technologies Ltd – a global leader in wind-assisted propulsion for commercial vessels – to supply and fit two vessels in their dry bulk fleet with Anemoi Rotor Sails.

Originally known as Flettner rotors, rotor sails are an energy-saving technology for shipping. These modern mechanical sails consist of tall cylinders that, when set in rotation, harness the renewable power of the wind to propel ships. This results in improved vessel efficiency and reduces the fuel consumption and release of harmful emissions into the atmosphere.

Anemoi Marine mentions that if their rotor sails were installed on every suitable vessel in the world fleet, the average savings per year would be: 17 million tonnes of fuel and 56 million tonnes of carbon.

How do rotor sails work?

Rotor Sails, traditionally known as Flettner Rotors, were first installed on ships in the 1920s after being invented by Anton Flettner. At the time, the technology was not widely adopted due to the rising popularity and low cost of diesel fuel. Now, 100 years later, this wind technology has garnered new interest in its ability to help lower emissions.

The Rotor Sails are driven to rotate by a motor. When a wind flow meets the spinning Rotor Sails, a pressure differential is created. This causes a thrust force which provides auxiliary propulsion to the vessel and can be used to increase the vessel speed or reduce the consumption of the main power unit.

Anemoi Rotor Sails Magnus Effect
When a wind current hits the spinning Rotor Sails, a pressure difference is created.

Rotor Sails have demonstrated increased vessel efficiency, reducing fuel consumption, bunker costs and harmful emissions. Compared to other wind propulsion technologies, Rotor Sails offer a much greater thrust force to propel the ship per square meter of sail area. This means they can be made more cost effectively and with less impact on vessel operation than traditional sails or wings.

Easy deployment

For vessels with complex cargo operations, such as Bulk Carriers, Anemoi has developed a patented Rail Deployment System. This allows their Rotor Sails to be moved along the deck of the ship so cranes can effectively load and unload without obstruction. Dependent on deck layout, the Rotor Sails can either be moved from side to side (transversely) or along the length of the ship (longitudinally). This system ensures the Rotor Sails have no impact on vessel operations.

Anemoi Rotor Sails Folding Deployment System
The Rotor Sails can be lowered for cargo operations and/or to allow the vessel to pass under low bridges.

If air draft and cargo operations both come into consideration, Anemoi also offers a Folding Deployment System. Rotors Sails fitted with this system can be lowered from vertical to horizontal, to allow the vessel to pass under low bridges and/or avoid impact to cargo loading and unloading.

Both the Rail and Folding Deployment Systems require minimal crew input and take only 10 minutes to complete operation.

Seamless installation and minimal maintenance

The number of Rotor Sails on a ship is determined by factors such as vessel size and deck space.

Rotor Sails can be installed on new ships or retrofitted onto existing ships. When retrofitting, installation is aligned to take place during standard or special surveys, with the Rotor Sails lifted on board in a matter of hours. Anemoi mentions that dry docking is not required for retrofit installation.

Anemoi says that their Rotor Sails have a lifespan of 25 years and require minimal upkeep. Any required maintenance is timed to align with typical vessel maintenance activities to ensure ship operations are not impacted.

Wide range of Rotor Sail sizes

Anemoi offers a wide range of Rotor Sail options. Their standard sizes are suitable for most vessel types. The company mentions that, “our cleverly engineered core design is easily scalable so we are able to tailor the Rotor Sail size based on individual vessel designs in order to optimise performance.

Having this flexibility means Anemoi Rotor Sails are suitable for almost all commercial vessel types, including all sizes of Bulk Carriers, Tankers, Gas Carriers, RoRos and Ferries.”

Source: Anemoi Marine