Oct 20, 2022 | Clean shipping articles and long reads

By Nick Contopoulos, COO Anemoi.

Wind propulsion, which was used to power ships for thousands of years before fossil fuels became readily available, is back on the agenda.

As a renewable resource, wind is the compelling option in the push towards industry-wide decarbonisation.

Rotor Sails make use of the aerodynamic phenomenon known as the ‘Magnus Effect’. As the cylinder rotates within an airflow, a forward thrust force perpendicular to the apparent wind direction is created, which delivers additional thrust to the vessel. The thrust generated can either provide additional vessel speed or maintain vessel speed by reducing power from the main engine. The tall cylindrical sails can be installed on the main deck, bow or elsewhere with sufficient space.

They were first installed on a vessel over 100 years ago. But through research, innovation and meticulous development Anemoi engineers have reimagined the technology for modern use.

In July 2022, Dry bulk owner Berge Bulk announced an agreement with Anemoi to supply and fit two vessels in their dry bulk fleet with Rotor Sails.

The first vessel, Berge Neblina, a 388,000 dwt Valemax ore carrier built in 2012, was made ‘wind-ready’ earlier in the year. The structural integration required prior to installing the technology was carried out during a scheduled dry dock. Four of Anemoi’s large folding deployment Rotor Sails will be installed to improve vessel performance. Folding Rotor Sails can be lowered from the vertical to mitigate the impact on air draught and cargo handling operations.

This flexible ‘wind-ready’ approach was taken to align with vessel availability and Anemoi’s production slots. The same approach has been taken with the second vessel, Berge Mulhacen, a 2017-built 210,000 dwt Newcastlemax bulk carrier, which is also receiving four folding Rotor Sails. Plan approval has been obtained for both ships from DNV.

The exciting partnership with Berge Bulk was further confirmation that forward-thinking shipowners are turning to wind-assisted propulsion to help them achieve their environmental objectives. The agreement proved once more that Rotor Sails are a realistic and workable solution that results in significant emission reduction. 

In October 2022, Anemoi reached an agreement with Cosco Shipping Heavy Industry Co (CHI), one of China’s major shipbuilding organisations. CHI has numerous yards capable of up to 7.5m dwt annual production across all major vessel segments and a significant global customer base.

CHI customers will now have the option to install Anemoi Rotor Sails on newbuild vessels or retrofit during dry dock. Under the terms of the agreement, the companies can offer a turnkey installation solution to customers.

CHI shares a long-term vision of the role that wind assisted technology can provide in delivering carbon reduction. Anemoi is planning a highly successful co-operation in the years to come and are already lining up the first installation opportunities.

A smooth installation process

Incorporating Anemoi Rotor Sails is a streamlined process because wholesale changes to the vessel structure, or dry docking, are not necessary. The Rotor Sails, along with all the necessary equipment, get delivered to the dockside. A specialist and highly-trained team then supervise the full equipment installation. Each Rotor Sail is installed in a single crane lift and connected to the foundation on the ship’s deck once the vessel integration work is complete.

Prior to this taking place, a feasibility study – which is unique to each vessel – will have been conducted to determine the optimal Rotor Sail positioning. This is to maximise performance within the vessel constraints and the required deployment system for the vessel.

The vessel integration stage is crucial to the process and Anemoi constantly supports clients at every stage, including the design and installation of the structural foundations and the electrical cabling from the vessel main switchboard to each Rotor Sail. The vessel integration can be completed during the construction phase of a newbuild vessel, or during a survey at a shipyard for a retrofit vessel.

Once the Rotor Sails are installed and all cables are connected, final commissioning of the system is completed prior to handover. This crucial stage ensures safe operation and compliance with Class requirements through rigorous testing.


Anemoi has developed a Fuel Saving Assessment Model (FSAM) to accurately predict fuel and emissions savings from various sizes and classes of vessel. Central to FSAM are four key data sets which are:

  • Rotor Sail performance data (harvested from Anemoi’s full scale UK test facility),
  • vessel performance data,
  • route data and
  • wind data.

FSAM uses this data to simulate thousands of historic voyages over a five-year period to ensure the results accurately reflect the wind conditions experienced on the chosen route. Any additional drag and increased generator usage are included so that the net results are fair and transparent.

For a 310,000-dwt VLCC trading the Bonny-Ningbo route and fitted with five Rotor Rails, FSAM predicts an annual fuel and emission saving of 13.5% which equates to 1,622t of fuel and the equivalent to 5,051t of CO2 saved each year.

Peak performance and automation

The Anemoi Rotor Sail System comprises the Rotor Sail itself, the foundation, deployment system (if required), wind sensors and electrical, control, and automation systems. The main components of the Rotor Sails are the ‘rotor’ (the cylindrical, rotating part), the support tower, upper and lower bearings, and the electrical drive system.

The rotor is built from advanced lightweight composite material and the tower is a steel column structure. Anemoi uses these materials to ensure maximum performance of its Rotor Sails and to withstand all weather conditions.

The Rotor Sails have a control station located on the bridge. This automatically controls the speed and direction of the Rotor Sails, as well as monitoring the performance and status of the system. The control system is designed to maximise performance and minimise crew input with automated speed and direction setting, equipment monitoring, safety features and performance reporting to stakeholders using a ship to shore data transmission.

Training and development

Anemoi Rotor Sails are built to last 25 years and have low maintenance costs. Regular maintenance would usually include:

  • periodic visual inspection of components and primary structural items,
  • bearing lubrication replenishment and
  • greasing of mechanical components.

Minimal crew input is required to use Anemoi Rotor Sails due to the automated control unit. However, to ensure the maximum benefit is extracted and the equipment is well understood, Anemoi provides full training for the crew and on-shore technical departments.

All Anemoi Rotor Sails are automated and respond to the wind conditions to maximise performance with no crew interaction required. All safety features, shutdowns and alarms are automatic. Crew interaction is required when using the company’s folding and rail deployment systems.

Eyeing the future

The shipping industry has a huge challenge to decarbonise. With emerging technologies, like Rotor Sails, becoming widely available and adopted in the market, wind can offer a solution to energy efficiency in the short, medium and long-term for both newbuild and retrofit. As other eco-technologies, energy-saving devices and alternative fuels become market ready, these can be used in conjunction with auxiliary wind propulsion to achieve enhanced environmental benefits.

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