Everything new is well forgotten old. A month ago, the largest ship with rotor sails, the first version of which appeared 100 years ago, completed its maiden voyage. The Sohar Max superbulk carrier, designed to transport 400 thousand tons of ore, arrived at the Brazilian port of Tubarao, using, in addition to the engine, five 35-meter rotor sails. The use of these sails allows saving up to 6% of diesel fuel, making cargo transportation less harmful to the environment.
Image source: Anemoi Marine Technologies
A patent for a rotor sail was issued in Germany in 1922 to the German engineer Anton Flettner. In 1924, the former sailing vessel was launched, equipped with two rotor sails instead of traditional sailing rigs. The operating principle of rotor sails is based on the Magnus effect, discovered in the 19th century. A rotating body creates a significant lifting force directed perpendicular to the air flow. If the wind blows against the side of a vessel with rotor sails, its energy is effectively converted into heading motion.
Rotor sails are significantly smaller in area than traditional ones, but create a more powerful pushing force. They are easier to handle, and the use of modern materials and computer technology further increases their advantages.
Today, the British company Anemoi Marine Technologies is designing rotor sails. Manufacturing and installation are carried out by Chinese contractors. The bulk carrier Sohar Max itself was built at a Chinese shipyard in 2012. The sails, 35 m high and 5 m in diameter, were installed on the vessel at the COSCO Zhoushan shipyard. They can be folded onto the deck during loading and unloading without interfering with the operation of port equipment.
While the vessel is moving, the sails are rotated by electric motors, creating thrust in the presence of wind. The first voyage showed that the use of active sails allows saving up to 6% of diesel fuel, reducing CO₂ emissions by 3,000 tons per year. The vessel operator is the Brazilian company Vale S.A. — on the wave of success, it ordered the modernization of another bulk carrier and plans to equip its entire fleet with rotor sails.