Wind-assisted Propulsion
Otilia Mojarro
Wind assisted propulsion is the practice of decreasing the fuel consumption of a merchant vessel through the use of sails or some other wind capture device. Sails used to be the primary means of propelling ships, but with the advent of the steam engine and the diesel engine, sails came to be used for recreational sailing only. In recent years with increasing fuel costs and an increased focus on reducing emissions, there has been increased interest in harnessing the power of the wind to propel commercial ships.
A key barrier for the implementation of any decarbonisation technology and in particular of wind-assisted ones, is frequently discussed in the academia and the industry is the availability of capital. On the one hand, shipping lenders have been reducing their commitments overall[1] while on the other hand, low-carbon newbuilds as well as retrofit projects entail higher-than-usual capital expenditure.[2][3][4] Therefore, research effort is directed towards the development of shared economy and leasing business models, where benefits from reduced consumption of fossil fuels as well as gains from carbon allowances or reduced levies are shared among users, technology providers and operators.[5][6]
The kite sail concept has recently received a lot of interest. This rig consists of flying a gigantic kite from the bow of a ship using the traction developed by the kite to assist in pulling the ship through the water. Other concepts that have been explored were designed to have the kite rig alternately pull out and retract on a reel, driving a generator. The kite used in this setup is similar to the kites used by recreational kiteboarders, on a much larger scale. This design also allows users to expand its scale by flying multiple kites in a stacked arrangement.
The idea of using kites was, in 2012, the most popular form of wind-assisted propulsion on commercial ships, largely due to the low cost of retrofitting the system to existing ships, with minimal interference with existing structures. This system also allows a large amount of automation, using computer controls to determine the ideal kite angle and position. Using a kite allows the capture of wind at greater altitudes, where wind speed is higher and more consistent.[8] This system has seen use on several ships, with the most notable in 2009 being MS Beluga Skysails, a merchant ship chartered by the US Military Sealift Command to evaluate the claims of efficiency and the feasibility of fitting this system to other ships.[9]
The third design considered is the Flettner rotor. This is a large cylinder mounted upright on a ship's deck and mechanically spun. The effect of this spinning area in contact with the wind flowing around it creates a thrust effect that is used to propel the ship. Flettner Rotors were invented in the 1920s and have seen limited use since then. In 2010 a 10,000 dwt cargo ship was equipped with four Flettner Rotors to evaluate their role in increasing fuel efficiency. Since then, several cargo ships and a passenger ferry have been equipped with rotors.
The only parameter of the Flettner Rotor requiring control is the rotational speed of the rotor, meaning this method of wind propulsion requires very little operator input. In comparison to kite sails, Flettner rotors often offer considerable efficiency gains when compared to the size of a sail or kite, versus the size of the rotor and prevailing wind conditions.[10]
Wind-assisted propulsion system (WAPS) technologies have gained significant attention in the shipping industry as a means of reducing fuel consumption and emissions. These technologies harness the power of wind to supplement the propulsion of a vessel by generation of aerodynamic forces. They have the potential to significantly improve the efficiency of shipping operations and make a meaningful contribution to the decarbonization of the industry, as wind is an inexhaustible, free, zero-carbon energy source.
Several different sailing technology concepts have been or are being developed, including rigid or soft wing sails, Flettner rotors and ventilated foils, or kites. Most modern systems now utilize state-of-the-art intelligent control and automation systems to operate in a safe manner and without the requirement for additional crew. A combination of advanced aerodynamics, automation, computer modelling and modern materials is unlocking a new generation of innovative sail systems for ocean-going ships.
WAPS have already delivered fuel savings of between 4.5% and 9%, according to vessel owners and operators, and have the potential to achieve savings of 25% if installed as a retrofit. The margins are potentially higher if newbuilds are particularly designed to carry sail systems.
Developing wind propulsion systems for onboard installation presents a range of challenges for shipowners, shipyards, ship designers, equipment manufacturers and technology providers.
The masts that support the rigid and rotating sails installed onboard ships can measure up to 80 meters high, taking up significant space on deck. The space required varies with the number of masts, which may reach up to four per ship, based on current prototypes. For ship designers and shipyards this represents a challenge, particularly for smaller vessels (e.g., fishing vessels, inland navigation vessels) that cannot accommodate such large masts.
Regulatory bodies such as the IMO have yet to produce official rules or guidelines for wind-assisted propulsion systems. Specific criteria have not yet been developed for commercial vessels, and compliance is carried out on a case-by-case basis. The shipping industry will need to adapt current regulatory frameworks to these new technologies, offering designers guidance on important aspects such as stability and visibility requirements.
One of the most innovative projects for wind-assisted propulsion is the CANOPE, a wind-propelled cargo ship built to transport ARIANE satellite launcher components from Europe to French Guyana. Jointly owned by Zephyr et Bore and Jifmar Offshore Services, the 120-meter ship will have four fully automated wing sails supported by a 30-meter mast. The ship will also be dual-fuel, LNG-powered, resulting in a 35% reduction in polluting emissions. Using its existing Rules for wind propulsion systems, Bureau Veritas will be classing the CANOPE, ensuring the safety and environmental compliance of the vessel.
As a leading classification society, Bureau Veritas is helping develop safe, sustainable wind propulsion methods and technologies. BV NR206 classification rules address safety and reliability from design review through to installation and operations, including maintenance and surveys. These rules help verify that clients have undertaken the necessary risk analysis, ship strength measurement, definition of load cases, etc., before adopting wind propulsion systems.
Bureau Veritas has also developed two new notations for wind-assisted propulsion, which provide load cases and coefficients for freestanding rigs, wing sails, kite sails and wind turbines. The WPS-1 notation is for wind-powered ships with standing rigging, and the WPS-2 notation concerns vessels with both standing and running rigging.
Bureau Veritas is also collaborating on a number of wind propulsion projects in addition to the CANOPE. Bureau Veritas experts are involved with the Ville de Bordeaux, a 20,000 DWT ro-ro cargo vessel with a kite system fitted onboard, owned by Louis Dreyfus Armateurs. Bureau Veritas is also working on Solid Sail, spearheaded by Chantiers de l'Atlantique. This project aims to develop a rigid sail made of glass-polyester panels that can be installed onboard large cruise ships.
Finally, as a member of the International Windship Association, Bureau Veritas is helping promote the development of wind propulsion solutions for commercial shipping worldwide.
Even though the total number of ships equipped with wind assisted propulsion systems is still at a comparatively low level, there is a perceptible increase in the number of ships that have installed or are planning to install these systems.
Wind-assisted propulsion technologies can potentially offer double-digit fuel savings and do not require specialist crew competencies or additional crew numbers. Due to these factors, the business case for retrofitting vessels with wind-assisted propulsion energy-saving devices is currently being explored and implemented by many industry stakeholders.
Wind-assisted propulsion retrofits such as suction sails, rotor sails (including Flettner rotors), rigid and kite sails offer a promising path for the shipping industry to move towards a more sustainable future. The technology is maturing, and with the right market conditions and regulatory support, it has the potential to become a widespread solution for reducing the environmental impact of maritime transport.
In response to the growing need for reduced energy consumption and the imperative to minimize carbon emissions, there has been a surge in the development of numerous energy-saving and cutting-edge technological ideas.
The urgency to find alternative propulsion methods requires innovative approaches and Wind-Assisted Propulsion is postulated to lead the change. Rooted in ancient maritime practices, it emerges as a key enabler in the decarbonization journey, with various types such as rotor sails, kites, suction wings, and rigid sails.
Regarding the goals outlined in the Paris Agreement, the International Maritime Organization (IMO) aims to achieve a minimum 40% reduction in total annual greenhouse gas (GHG) emissions by 2030, compared to the levels recorded in 2008.
Dassault Systmes has become a pivotal force in implementing digital technologies in shipbuilding and marine environments. Our focus lies in integrating Wind Assisted Propulsion Systems, as the most sustainable solution to reduce fuel consumption through retrofitting sails on existing ships.
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