ferry. The company also recently announced the results of a one-year installation of two 30 x 5 m rotor sails on the Maersk Pelican, a 109,000 DWT tanker. The results of this test were analyzed by the Lloyds Register, which stated that fuel savings in one year were 8.2%.
The current momentum of technology will undoubtedly lead to more applications in the years to come. But it is clear that the role of the new hybrid electric systems assisted by wind propulsion to reduce emissions will not stop only in the commercial transport sector, but will also affect the pleasure market.
The SKS-Y system Image 3 VPLP-RO-RO VESSEL
Despite all these evolutions and improvements in the soft wing sector, rigid wings are still preferred because they can incorporate aerodynamic structures or photovoltaic coatings. Research is currently underway in this area exploring the application of the technology to ships of various different sizes. In a recent development, Japanese companies Mitsui OSK and Oshima Shipbuilding received approval in principle from the ClassNK maritime classification body for the construction of a 100,000 DWT transport vessel equipped with a telescopic sail system that the group says it could reduce fuel consumption by up to 8%.
While the ability to automate, use new materials and data to optimize performance is attracting a lot of interest from both owners and designers, there are still many issues that need to be addressed as size increases: 1- the systems can take up large amounts of deck space;
2 - and they can also induce a significant amount of heeling (or tipping from side to side) in the ship.
One concept that potentially overcomes this problem is a vertical, deck-mounted foil called “suction wing” which is presented as capable of delivering considerably more power per square meter than a normal sail at a fraction of the height.
The Flettner Rotors, named after the aeronautical engineer Anton Flettner (1885-1961), are also used for wind navigation. They consist of a vertical axis cylinder with fixed or movable blades, which create a motor moment
that rotates the cylinder around its vertical axis and a suction like around the supporting wing of an airplane. The first merchant ship propelled by two Flettner rotors was the Buckau which in 1926 sailed as far as New York. In the following years, however, the owners preferred ships powered by steam or diesel engines. Now, that the focus is very much on reducing fuel consumption, costs and sustainability, advocates of wind-powered transport are increasing and the Flettner rotor is being taken seriously by some of the major players in the naval sector.
The Flettner rotor operates by exploiting a curious aerodynamic phenomenon known as the magnus effect, the same force that causes a spinning tennis ball to swing. Resembling vertical cylinders mounted on the deck of a ship, these motorized devices rotate around their own axis. The rotation speed can be adjusted according to the wind speed and direction, and the interaction between the rotor surface and the wind creates a lifting force that generates additional thrust.
While a number of companies are actively working on developing the technology, the leader in terms of the number of installations is the Finnish company Norsepower. Its Rotor Sail technology, if applied to the entire global tanker fleet, would reduce annual emissions of CO2 by over 30 million tons.
In 2018, Rotor Sail was installed on Viking Grace, an LNG-powered passenger ferry. Last year Norsepower announced plans to install a 30-meter-high system aboard the M/V Copenhagen, a hybrid passenger
Hamburg-based SkySails is now launching the yacht version of its system consisting of three main components: • A kite • A launch and retrieval system • A control system for automatic operation
As with commercial ships for propulsion, large kites made of high- tech, high-strength fabrics are used. Recreational SkySails also operate at altitudes between 100 and 300m. The launch and retrieval system manages the movement of the kite and is installed on the bow. During launch, a telescopic mast lifts the kite from its storage compartment. At a sufficient height the kite unfolds to its full size. A winch releases the tow rope until the operating altitude is reached. The recovery process is performed in reverse order.
The entire setup and recovery procedure takes between 10 and 20 minutes. The latest generation of products features a 400 m² fully automated kite capable of replacing up to 2 MW of the propulsion power of a ship's main engine.
Even the smallest kite can replace up to 250 kW of engine power in good wind conditions. Since the engine usually only runs between 0 and 5% of the time, the yacht owner is more independent and has the opportunity to sail where he wants while saving fuel. SkySails combines the advantages of sailing with those of motor sailing. Numerous customization options are available to meet the special needs of super yacht customers, for example logos and insignia can be printed on the towing kite and the mast can be adapted to the yacht design.
The Report • June 2021 • Issue 96 | 67
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