EcosNavis Solutions is developing a next generation wind-assisted propulsion system designed to enhance the performance and commercial viability of Flettner-type rotor sails for deep-sea shipping.

The company’s Eco Rotor Sail introduces a patented tail-appendage device designed to increase thrust, reduce power demand, and widen the range of wind angles in which rotor sails can operate efficiently.

Flettner rotors – rotating cylindrical sails first introduced in the 1920s – are enjoying a come back as shipowners seek credible ways to cut fuel consumption and greenhouse gas emissions. But a major deterrent to much wider take-up is performance reliability when the wind direction changes. Anton Flettner’s underlying principle has changed little in more than a century.

Polar diagram at a 25m/s True Wind Speed comparing a conventional Flettner rotor with the tail-appended Flettner rotor.

The EcoNavis design, however, essentially broadens the rotor’s effective “wind window” by reshaping the wind flow in the rotor’s wake to deliver higher thrust with lower torque demand.

According to the Glasgow-based innovator, initial simulations indicate an increase in thrust of up to ten per cent alongside a five per cent reduction in torque.

The Eco Rotor Sail retains the conventional rotating cylinder but introduces a fixed aerodynamic appendage downstream to stabilise the airflow behind the rotor, reducing losses and allowing the system to continue generating thrust as wind conditions change.

“Flettner rotors already offer one of the highest lift-to-drag ratios among wind-assisted devices, with a relatively modest footprint, but the main drawback has been the narrow band of wind angles – typically beam and stern-quarter winds,” said EcoNavis CEO and founder Dr Batuhan Aktas. “The Eco Rotor Sail expands the range of wind angles over which the rotor can operate efficiently.”

The flow regime, represented by the same scale of the wind speed, behind the standard (left) and tail-appended (right) Flettner rotor

Aktas said compared to existing rotors, the new design strengthens the case for the technology on larger commercial tonnage. “It offers more energy savings and lower operating costs,” he said.

“By recovering energy that would otherwise be lost and optimising the flow behind the rotor, we can provide a Fletner rotor design with a greater operational range. This means shipowners can have greater flexibility in route planning and more consistent performance over a typical trading year, without fundamental changes to vessel operations.

“If you can maintain performance across a wider range of conditions, you change how the technology is used. It becomes something operators can plan around, rather than something that depends on favourable weather,” Aktas said.

Cargo ship with rotor sails at sea

Eco Rotor Sail development is backed by a £100,000 research grant from Scottish Enterprise to take the £265,000 project through to validation and demonstration stages. The next phase will move into physical testing.

EcoNavis plans to build a scale model for wind tunnel trials at Politecnico di Milano, Italy, to validate performance and correlate results with simulation data.

Subject to successful validation, a full-scale prototype could be built this year for shipboard trials as part of an integrated power system.
Source: EcoNavis