The winds of change – how rotor sail technology can boost maritime decarbonization efforts


Aegyptian pioneer sailors sailed the Nile, the Mediterranean and the Red Sea using the power of the wind, laying the foundations for a time when sails dominated navigation before the rise of steam power in the late 1800s. Today, with pressing climate challenges to tackle and strict emissions restrictions to adhere to, the maritime industry is once again turning to Mother Nature for a helping hand.

“Rotor sails, also known as Flettner Rotors, are modern mechanical sails – large cylinders which, when spinning in circles, provide additional propulsion power to ships and thus reduce the amount of fuel consumed at board,” says Elias Boletis, Director of Propulsion R&D at Wärtsilä.

“They are an exceptionally environmentally friendly way to generate additional propulsion force as wind power is completely renewable, and they are also an extremely flexible solution that can easily be integrated onboard a wide variety of ship types. vessels without affecting their operational viability.”

Harness the Power of the Magnus Effect
When the wind speed and direction are optimal, the rotor sails, which are powered by electric motors, can be activated automatically. When the wind meets the sail, an aerodynamic phenomenon called the Magnus Effect means that the air in front of the sail accelerates as it is pulled in the direction of rotation. This faster moving air has a lower pressure while the air behind it slows down and increases in pressure – and this pressure difference propels the ship forward.

Big savings thanks to simple and flexible technology
Installing rotor sails can result in a 5-30% reduction in fuel consumption and emissions. These gains are a welcome boost for shipowners as they develop their roadmaps to tackle tougher regulations. These include the Energy Efficiency Index for Existing Ships (EEXI), which defines a minimum level of energy efficiency for existing ships, and the Carbon Intensity Indicator (CII) scoring system. , which assigns vessels an annual rating on a scale of A to E, with A being the least carbon intensive.

Wärtsilä is an authorized seller and service partner of the Anemoi Marine Technologies rotor sail system, which is particularly well suited for bulk carriers.

Anemoi has developed its own method for evaluating fuel savings in order to develop reliable performance forecasts for potential customer vessels. To give an example, this method predicts an annual fuel and emissions saving of 13.5%, or 1,622 tonnes of fuel and 5,044 tonnes of carbon, for a 310,000 dwt tanker with five rotor sails sailing on a route between Nigeria and China.

In June 2022, a student joint development project Anemoi Rotor Sails received approval in principle from Lloyd’s Register, which validated that a 210,000 dwt Newcastlemax bulk carrier operated by Oldendorff Carriers could reduce its design index score by 29% energy efficiency by installing six 5 x 30m rotor sails. But fuel and emissions savings only tell part of the story.

For example, Anemoi offers options for folding sails, which fold towards the deck during handling operations, and track-mounted sails which can be moved longitudinally or transversely away from cranes or other lifting equipment.

A transferable investment in decarbonization
“Once the vessel is ready, the owner can choose to install the rotor sails in stages at appropriate ports of call, using a plug-and-play approach. And if the vessel’s operational profile changes or the vessel is sold, the sails can simply be removed and transferred to another vessel – an advantage that is simply not possible with some other energy-saving technologies. In that sense, rotor sails are what you might call transferable CAPEX,” shares Elias.

Integrate to accumulate
When it comes to optimizing the energy efficiency of a new or retrofitted vessel, Wärtsilä takes a holistic approach to developing an integrated system that delivers significantly more value than the sum of its individual components. “Prior to installation, a full feasibility study is carried out to determine the optimum number and position of rotor sails. With our integration expertise, we can ensure that the rotor sails are integrated in a way that provide maximum propulsion advantage and that they complement the main propeller and other energy saving solutions on board.At the same time we can plan the integration so that the rotor sails n have no negative impact on the vessel’s course-keeping or maneuvering performance,” says Elias.

The Optiwise project gives wind propulsion a boost
Launched in 2022, the EU-funded Optiwise project aims to maximize the energy savings of wind propulsion technologies, with the aim of achieving average energy savings of between 30 and 50% compared to ships with conventional propulsion. Both Wärtsilä and Anemoi are participating in the project, with Wärtsilä as OEM driving technology integration at ship level, providing systems expertise and streamlining technology innovation to meet the needs of the maritime market.

“At sea, the wind is all around us and is a free source of energy when harnessed efficiently. With rotor sails such as the Anemoi system, shipowners can achieve significant efficiency gains that could mean the difference between meeting or missing the increasingly tight efficiency targets on the horizon. The time has come to put the sails back in the sail. Elias concludes.
Source: Wärtsila


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