In Depth: Wind Assisted Propulsion – Flettner Freighter Design for Switijnk Shipping

As Maritime Holland readers undoubtedly know, the 2015 Paris Climate Agreement makes no reference to the shipping industry. However, this doesn’t mean that the sector is not making its own progressive steps on the matter. The recent contract between Switijnk Shipping, a family-owned Dutch shipping company, and C-Job Naval Architects for a Flettner Freighter is one example of how the shipping sector is independently and pro-actively looking for sustainable shipping solutions. 

Before we start, it is probably a good idea to have a quick recap on the concept of Flettner ships. They are a type of ship that uses the Magnus effect – a force that acts on a spinning body in a moving airstream – for propulsion. In Flettner ships, these spinning bodies are tall rotating cylinders on the deck that are powered by a motor. Because the Magnus effect acts perpendicularly to the direction of the airstream, the optimum wind direction for Flettner ships is from side winds. Anton Flettner, a German engineer, built the first example, the Buckau, in 1924. It was this vessel, renamed the Baden Baden, that successfully crossed the Atlantic in 1926.

Rotor Sails in action

Although the Flettner concept of propulsion never really gained momentum back in the 1920s, the idea has garnered more attention in recent times. Why? Most probably because the priorities of the modern world have changed considerably since the early twentieth century. The modern maritime industry is faced with a range of complex issues involving oil production and pricing, as well as increasing environmental regulations and awareness.

Switijnk Shipping’s decision to call on C-Job Naval Architects is perhaps a logical reflection of this, as managing director Stefan Switijnk highlights: “Sustainable development is part of our future-proof philosophy as a family business.” The C-Job design will be a 131-metre long, 8,000 deadweight tonnage dry cargo ship – taking the project name of FF8000. The vessel will be equipped with two Rotor Sails; the modern version of Anton Flettner’s rotating cylinders that are marketed by Finnish company Norsepower. Switijnk describes his first encounter the Rotor Sail set up: “We were invited on board the Estraden [a car carrier equipped with Norsepower Rotor Sails] and we were very impressed by the whole system. It is fully automated with a very user-friendly interface. The Estraden is also a fast ship.”

Key decisions 

A crucial part of the design phase has been to analyse average wind conditions on Switijnk Shipping’s predominant sailing routes. In terms of fuel consumption, this has generated some attractive results: “We are expecting fuel savings to be in double figures, which will also significantly reduce our CO2 emissions.” However, this fuel efficiency means that some unexpected decisions will have to be made, says Switijnk. “Our fuel use with this design will be so low that we are rethinking our initial decision to use LNG as main engine fuel. In terms of things like investment, personnel training and certification; will it be the wisest choice?”

Maximising thrust 

For this project, C-Job has been able to draw on the experience it gained from penning a 4,500 deadweight tonnage concept design (the FF4500) for a Rotor Sail equipped Flettner Freighter for the European Union Interreg project SAIL. The most visible difference between the two designs it that the vessel for Switijnk Shipping will be fitted with two Rotor Sails instead of four; thus removing the possibility that the rotating cylinders will affect each other’s wind shadow. “Supplementing engine power with wind is a pure hybrid system. This is a very efficient technique – gaining a high yield from the wind. And it is a system that requires minimal handling and low maintenance,” notes C-Job Naval Architects Business Manager Jelle Grijpstra.

“This is a plug and play concept. You need a foundation for the rotors and, because the technology is based on a moving object in an airstream, you need to supply about 75 kilowatt to get the rotor sail moving at the right revolutions per minute. After that, the system’s software adjusts the rotation speed to deliver maximum thrust. Our involvement has been to design a ship that maximises forward propulsion using the Norsepower Rotor Sails.” There is also potential for this wind assisted propulsion in other vessel types, notes Grijpstra: “This technology is also suitable for oil tankers, cruise ships and ferries – although the matter of air draught needs to be taken into account.”

Showing potential

The attention that the Rotor Sail technology is receiving is certainly increasing – Norsepower won the ‘Innovation of the Year’ award at the Electric and Hybrid Marine World Expo in Amsterdam this year. Furthermore, the Finnish company recently received € 2.6 million from the European Commission and the Finnish Government’s funding agency for innovation to further its research and development programme.

For Switijnk Shipping’s managing director, cleaner shipping has a future. “It’s still early days, but you have to start somewhere,” says Switijnk. “There is so much potential for this technology in coastal shipping industry in North West Europe.” He is currently focusing his attention on finding partners to develop and finance the project: “While the technical aspect is the most exciting, the financial aspect will be the most challenging.”

Tom Scott

This article was previously published in Maritime Holland edition #6– 2016.

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