Sustainable wind power for the maritime sector

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The maritime sector is under significant pressure to reduce emissions of greenhouse gases and other harmful substances. Radical changes are required to comply with increasingly stringent international regulations and to meet the growing demand for CO₂-neutral transport. Wind-Assisted Propulsion Systems (WAPS) provide shipping companies with directly deployable technology to reduce fuel consumption and emissions. The systems harness wind energy as an auxiliary source of propulsion.

‘WAPS make an important contribution to the energy transition. We notice that more and more vessels are being equipped with the technology. We applaud this and are, of course, pleased to welcome these vessels to our port,’ says Hanneke te Niet, Harbour Master Policy Advisor at the Port of Rotterdam Authority. The port of Rotterdam has been familiar territory for sailing ships for centuries. Even in their modern, sustainable form, such vessels are increasingly frequent visitors to the port. Sea-Cargo’s SC Connector is among them. The shipping company owns and operates a modern fleet of multifunctional vessels designed to carry various types of cargo. After five years of preparation, Sea-Cargo launched its first vessel fitted with a WAPS installation in 2021. ‘Wind is free and non-polluting. Furthermore, our CO₂ emissions have decreased markedly, resulting in lower ETS payments and fewer costs being passed on to clients. This provides us with an additional competitive advantage,’ says Siebe Kramer, General Manager at Sea-Cargo. But what precisely are WAPS, and are there any restrictions that shipping companies must take into account?

Various WAPS technologies

WAPS encompass several technologies. The most commonly used are:

• Rotor sails (Flettner rotors)
  Rotor sails are cylindrical structures that rotate on their axis and utilise the Magnus effect, which generates a lift force that serves as additional propulsion for the vessel, thereby reducing fuel consumption. Rotor sails are relatively compact and modular, which often makes retrofitting on existing vessels feasible. Rotor sails require sufficient clearance and stability to accommodate the additional forces generated.
• Wing sails
  These stiff wing sails have a profile similar to that of aircraft wings. Due to their fixed shape, they offer high aerodynamic efficiency but require robust structures and more free space on the deck.
• Suction sails and soft sails
  Suction sails combine traditional sail shapes with air suction across the surface to increase lift. Soft sails, frequently designed to be flexible, offer a lighter solution and can be stored more easily when not in use.
• Kites
  These autonomous kites operate at higher altitudes (100–300 metres), where winds tend to be stronger and more consistent. Kites have minimal impact on deck space but necessitate specific operational procedures for deployment and retrieval. These systems are particularly suitable for vessels navigating long ocean routes.

More than just fuel savings

‘The choice of WAPS technology depends on factors such as vessel type, shipping routes and operational constraints,’ Kramer explains. Sea-Cargo opted for a Flettner system, comprising two rotor sails each measuring 35 metres in height and five metres in diameter.

For shipping companies and ship owners, a WAPS installation offers immediate financial benefits. Depending on the system’s type and size, as well as the sailing route and wind conditions, a wind-assisted propulsion system can deliver annual fuel savings of 5 to 20%, with peaks exceeding 25% under optimal conditions. ‘An additional advantage is that the rotor sails provide the vessel with enhanced stability, thereby reducing the risk of cargo shifting,’ Kramer adds.

Sea-Cargo is sufficiently convinced of the benefits that the shipping company has decided to convert two additional vessels. It hopes to commission the new systems later this year. In addition to the improved WAPS, further modifications have been made to these vessels to reduce CO₂ emissions. ‘With all these adjustments, we anticipate fuel savings of up to 50%,’ says Kramer.

No drawbacks or restrictions

The general manager notes no disadvantages, not even during port calls. ‘Due to the height of our current rotor sails, restrictions apply in certain ports, such as at terminals and bridges. However, because we have constructed the cylinders so that they can be folded, those restrictions no longer apply. And in Rotterdam, there are absolutely no restrictions,’ says Kramer.

‘Rotor sails and wing sails are classified as fixed ship equipment and are therefore not subject to additional regulations when navigating the port,’ Te Niet explains. ‘Because sails are lowered, rotor sails are retracted, and the systems typically stay within the vessel’s contours, the presence of a wind-assisted propulsion system rarely impacts the port call.’ The port of Rotterdam therefore does not have a specific wind or WAPS protocol, nor does it appear that one will be introduced. Simply because there is no justification for it.

‘Should a system nevertheless extend beyond the vessel’s contours, or should the vessel’s manoeuvrability be reduced due to an increased wind surface, this specific case may require a tailor-made approach, and a harbour master may impose additional measures. After all, you don’t want any contact with a port crane, for example, or for the systems to be damaged,’ adds Te Niet. However, this is not anticipated, not least because WAPS are constantly being further developed, in part to facilitate the most efficient organisation of port calls.

Future perspective

The WAPS market is expected to experience significant growth in the coming years. With an average payback period ranging from three to seven years – depending on system type, fuel prices, and subsidy programmes – WAPS represent a financially attractive investment. ‘Especially as WAPS have little or no impact on processes within the port, they make an essential contribution to the maritime energy transition,’ says Te Niet.

Combined with alternative fuels and optimisation software, wind-assisted propulsion can become a key component in advancing more sustainable shipping. Wind, long the driving force behind maritime trade, is once again assuming a pivotal role in the future of the maritime sector.