According to EMSA, the maritime industry faces substantive challenges due to increasingly strict air emissions and climate legislation as its practitioners navigate the course towards decarbonisation. The potential of wind assisted propulsion systems as a power source in the shipping sector is analysed in a new report released by EMSA.
Among the broad spectrum of technologies and fuel solutions being considered, wind-assisted propulsion systems (WAPSs) are seen as a technology that could reduce the fuel consumption from ships and, consequently, lower their greenhouse gas (GHG) and other emissions.
Wind-Assisted Propulsion Systems
As explained, wind propulsion systems are designed to transform wind energy into ship-propulsion power. Depending on the specific type of technology, different physical principles are used in this energy conversion. In addition, the technologies may be distinct in their approach to implementation and installation. Six categories of wind propulsion technologies are distinguished: rotor sails, hard sails, suction wings, kites, soft sails and hull technology. Aside from these systems/designs, wind turbines for electricity generation on board ships also are being developed. The focus of this study, however, concentrates on the wind propulsion
systems that can directly contribute to the propulsion of a ship. It presents an overview of current wind propulsion technologies for maritime shipping, based on literature reviews, internet research, information from the technology providers and input from the International Windship Association (IWSA).
- Rotor sails (traditionally also known as Flettner rotors) are spinning rotors, driven by small electric engines that are vertically mounted on the deck of the ship. The active rotation, together with the wind, creates a pressure difference on the cylinder orthogonal to the wind direction – the so-called ‘Magnus
effect’ – that in turn provides a propulsive force (ScandiNAOS AB, 2013). - Hard sails function like traditional soft sails: aerodynamic lift and drag forces are generated by the interaction between the wind and the sails. Hard sails, however, have a rigid geometry and are made of light and strong materials such as carbon fibre. Generally, the sails can be rotated to adjust to wind
directions and to maximise propulsion, a function that is often automated. Most hard sails are wingshaped sails, which is why they are also referred to as wing sails. - Suction wings are wing-shaped vertical structures that are mounted onto the deck. In contrast to rotor sails, their outer parts do not rotate to generate thrust, although the wings are orientable, i.e., they can be rotated automatically to adjust to the direction of the wind.
- Kites can be attached to the bow of a ship to generate lift and drag. They need to be launched/retracted, depending on the wind conditions, for which automated systems have been developed. Compared to other technologies, kites can make use of the higher wind speeds found at higher altitudes, although there is a trade-off between altitude and drive-force due to the increase of the elevation angle (Dadd, Hudson, & Shenoi, 2010).
- Soft sails are flexible sails like traditional sails. Just like hard sails, some modern soft sails are wingshaped to maximise the force of the thrust. In some designs, the masts of the sails serve a double function as cranes, to also be used for loading and unloading. Another approach are inflatable soft sails
(Michelin, 2022).
GHG Reduction Potential
The performance, fuel and emission reduction potential of WAPS depend on several internal and external factors. These factors include:
- WAPS-related factors:
- Type of WAPS
- Number and dimensions of WAPS units
- Position of WAPS units on the ship
- Type of installation (retrofit or newbuilding)
- Operation/automation
- Environmental factors:
- Weather conditions
- Ship-related factors:
- Technical characteristics
- Operation of the ship
- Crew training
