What Are Rotor Sails On Ships?

The Rotor sail was named after the German aviation engineer and inventor Anton Flettner, who started developing the rotor sail in 1920.

Rotor Sails have improved vessel efficiency by lowering fuel use, bunker expenses, and hazardous pollutants. Rotor Sails provide significantly more thrust force per square meter of sail area than other wind propulsion methods.

Let us get into more details to find out how the function of the rotor and much more.

What Is The Magnus Effect?

Ever wondered why a tennis or golf ball curves during its flight path? The scientific reason behind this is the Magnus effect.

Magnus effect is when wind meets the spinning rotor sail, the airflow accelerates on one side of the rotor sail and decelerates on the opposite side creating a pressure difference.

Thrust is produced by the rotation of the sails in an airflow, which results in a pressure differential on the rotor’s aft and front surfaces. This thrust force is determined by wind angle and speed; the greatest thrust is produced when the wind direction is directly from the beam.

In operation when the rotor is switched on and starts rotating in presence of wind, the change in the speed of airflow results in a pressure difference which creates a lift force that is perpendicular to the direction of wind flow. This provides the ship with an additional forward force which reduces the engine’s fuel consumption.

The Magnus Effect used in rotor sails
The Magnus Effect used in rotor sails

How Does The Rotor Function?

There is an end plate fitted on the rotor which is used to optimize its aerodynamic efficiency. The crew has control of the rotor sails from the control panel on the bridge, also some systems can automatically monitor the wind and speed direction to determine the optimal rotational direction and RPM values which thereby maximizes the fuel savings for the vessel.

The rotor sails are mounted on vessels’ tailored foundations which also house a variable drive motor that can control the speed and direction of the rotor.

Flettner rotors are vertical cylinders that spin and generate lift forces due to the Magnus effect. These lift forces support the overall thrust forces acting on the hull for propulsion thereby reducing the loads on the main engines.

The total number, size, and location of rotor sails depend on the following factors,

  • Available deck space
  • Location of the structural members on the deck
  • Vessel operation parameters and functions

What Are The Benefits Of Rotor Sails?

Most rotor sail manufacturers make sure that the rotors are designed and certified in line with the norms of the world’s main classification societies, assuring compliance with the highest maritime quality requirements.

The main benefits of rotor sails are ship performance and environment improvement, lightweight and flexibility, endurance, safety and compatibility, and versatility.

  1. Lightweight – Rotor Sails are made of the most modern composite structures and the most advanced manufacturing process to come up with lightweight yet strong materials to ensure exceptional performance while adding as little weight as possible. A sturdy steel tower at the center of the Rotor Sail securely transfers all loads into the ship structure.
  2. Endurance – By Class Requirements, rotors are intended to endure the most severe weather conditions as they stand very high above the main deck. Rotors can be designed for high seas and winds to withstand up to 35m/s (70kts). Some automated rotor sails automatically shut down in harsh situations that exceed their working limits. Reefing is not necessary, as it is with other wind technologies.
  3. Compliant with regulatory bodies – A 5-30% reduction in hazardous emissions such as CO2, SOx, and NOx benefits the environment while also assisting vessels in meeting regulatory requirements and objectives. Rotor Sails have a favorable influence on a newbuild vessel’s EEDI score and can give a path to compliance with the forthcoming 2025 Phase 3 standards, as well as improve possible operational indicators for retrofit installations (e.g. EEXI and CII).
  4. Performance benefits – Annual economic savings potential of 100 000 – 200 000 EUR per Rotor Sail under global average wind conditions.  Typical average fuel savings of 5-20% per ship.
  5. Environment Benefits – The biggest Rotor Sail type has an annual average savings potential of roughly 300-350 kW. Annual fuel savings of around 300-400 tons. A 900-1200 ton decrease in yearly CO2 emissions.
  6. Movable – Sails may be redeployed between vessels based on operational needs, giving owners confidence in the lifetime of their investment and ensuring return.
  7. Safety and compatibility – Rotor Sails are appropriate for a wide range of vessel types, including newbuild and retrofit, Bulk Carriers (geared and gearless), Tankers, LNG and LPG Carriers, Ferries, and RoRo ships.

Technical and Materials

The Rotor Sail System is made up of the Rotor Sail, the Foundation, the Deployment System (if needed), wind sensors, and the Electrical and Control System. The following diagram depicts the position of the equipment.

The “Rotor” (the cylindrical, revolving section), the Tower, the Upper, and Lower bearings, and the electrical motor are the four basic components of our Rotor Sails. The “Rotor” is composed of lightweight composite material, while the Tower is made of steel columns.

The material selection is based to guarantee that the Rotor Sails operate well in all-weather situations. with the use of advanced composite like carbon fibers, the rotor sail systems are often less than 0.1% of the vessel’s deadweight.

The Rotor Sail System
The Rotor Sail System

Controls And Electronics

A Control Station for the Rotor Sails is positioned on the bridge. This automatically regulates the speed and direction of the Rotor Sails while also monitoring the system’s performance and status. With automatic speed and direction setting, equipment monitoring, and safety shutdowns, the rotor sail control system is designed to maximize performance while minimizing crew involvement.

The electrical input power needs of the Rotor Sails vary with Rotor speed, which is affected by wind speed. When operational, the average power input of one Rotor Sail is approximately 40% of the rated power of the motor. A Rotor Sail with a 75kW motor, for example, would utilize 30kW on average.

Location and control of Rotor Sails On Ships
Location and control of Rotor Sails On Ships

Companies providing rotor sail technology and vessels that have them

The following are a few of the major industry-leading companies which provide rotor sail technology and have successfully installed them on different kinds of vessels.

NORSEPOWER

A company named NORSEPOWER which is a leading sail technology provider has already installed rotor sails on different types of vessels such as tankers, dry cargos, and passenger vessels. Norsepower’s Rotor Sail system is the first complete commercial mechanical sail that has been third-party confirmed. The completely automated control system detects favorable wind conditions and operates the Rotor Sails with no intervention necessary from the crew.

The company has recently installed two 35m high world-first tiltable rotor sails, which allow the vessel plying in height-resisted routes to benefit from this technology to save fuel. The range of cost for a Flettner rotor varies from $1 000 000-$4 000 000 depending on the size and utility.

Anemoi

This company was started in 2007 to combat the global emissions from the shipping industry and to come up with a design solution that could revolutionize the industry. From the period 2008-2014, they started working on the Flettner rotor technology and even developed a full-scale model for testing and trials.

At present, they deliver clients with outstanding design solutions which include rotor sails that can be retractable and even removable which gives the owner flexibility in different operational conditions.

Hyundai

Hyundai, based in South Korea, has been working on a new rotor sail design to help in environmentally friendly shipping throughout the world. This is gaining popularity in the maritime sector as a feasible method for reducing carbon emissions. When in use, this new system is said to reduce carbon emissions and fuel consumption by 6% to 8%.

Design Approval for Hyundai Heavy Industry Hi-Rotor
Design Approval for Hyundai Heavy Industry Hi-Rotor

Hyundai stated that its design “improves the stability of the drive system compared to the belt method of existing commercial products by applying the reduction gear method to the driving part connecting the electric motor and the rotor.”

The system has been named the Hi-Rotor, and Hyundai expects to undertake land demonstrations with it by the end of 2022, after having their Rotor Sail system Approved in Principle by the Korean Register of Shipping.

Rotor Sails Summary

The rotor sails are efficient solutions in terms of reducing fuel consumption and emissions and can have a huge role in decarbonization in the maritime industry. Shortly, we can find more vessels that implement the rotor sail technology making them more efficient.

Why Do Trawlers Have Sails?
Why Do Trawlers Have Sails?
Rotor Sail explained