The Magnus effect, named after Heinrich Gustav Magnus, is a phenomenon in fluid mechanics and describes the force that a rotating round body experiences in a flow.
A Flettner rotor is specifically a rotating cylinder around which the wind flows. The rotation creates a force that acts transversely to the direction of the wind.
If wind blows against a rotating cylinder, the air flow is accelerated on the side where the wind direction and the direction of rotation are the same. On the other side, the direction of rotation is reversed and the air is slowed down.
This creates negative pressure (faster flow) and positive pressure (slower flow) on the cylinder. This results in a force acting on the cylinder The Flettner rotor is both pulled forward and pushed. This force acts transverse to the wind direction and generates the propulsion of the ship.
The Flettner rotor is an old concept that is constantly being improved with modern technologies and materials. The aim is to reduce emissions in shipping and thus take a big step towards environmental and climate protection. The results are excellent.
The efficiency of the rotors is heavily dependent on wind strength and direction, as well as the route of the ship. However, independent analyses have shown that the use of Flettner rotors can save up to 25 percent fuel.
The first rotor ship was developed and converted by Flettner as early as 1924, the "Rotor Ship Buckau" had two 13 meter high Flettner rotors. However, these were not successful and lost the economic competition against steam engines and diesel engines in the years after 1930.
Nowadays, Flettner rotors are installed on ships as an auxiliary drive to create an energy-saving hybrid drive.