A Flettner freighter in the making

For
centuries shipping depended on wind, but the industrial revolution changed that.
No longer vessels were stuck in the doldrums. Today, with the Paris Climate
Agreement in mind, shipping companies are looking at wind again for efficiency
reasons. Recently C-Job Naval Architects has delivered the design for a
wind-assisted general cargo vessel to Dutch shipping company Switijnk Shipping.
The 8,500 DWT vessel will be equipped with two Norsepower Rotor Sails that will
supplement the main engines and is expected to achieve fuel savings of
approximately 14 per cent.

This vessel,
called the FF8500, is a Flettner ship. They are a type of ship that uses the
Magnus effect. In the design Rotor Sails are deck-mounted rotating cylinders
that utilise the Magnus effect to create a propulsive thrust. The Magnus effect
is a force that acts upon a spinning ball or cylinder in a moving airstream.
Although the phenomenon is named after the German physicist, Heinrich Gustav
Magnus, who described it in 1852, it was originally observed by Isaac Newton almost
two hundred years earlier. The name Flettner ship comes from Anton Flettner, a
German engineer, who built the first vessel, the Buckau, using this effect in 1924. This vessel successfully
crossed the Atlantic in 1926.

C-Job Naval
Architects was approached by Switijnk Shipping following its involvement in the
European Union Interreg project S@IL, for which C-Job developed the earlier
design of a 4,500 DWT Flettner Freighter. C-Job designed this smaller vessel
with four Rotor Sails. However, after studying the prevailing wind patterns on
Switijnk’s proposed sailing routes, C-Job decided to design a new vessel with
two larger Rotor Sails. The Magnus effect acts at 90 degrees to the direction
of the airstream. Because the Magnus effect acts perpendicularly to the
direction of the airstream, the optimum wind direction for Flettner ships is
from side winds.

“Our
experience from the Project S@IL study showed that Rotor Sails were the most
viable choice compared to other wind assisted propulsion systems,” explains C-Job
Business Manager Jelle Grijpstra. “And then, together with Finnish Rotor Sail
supplier Norsepower, we concluded that two larger Rotor Sails were most
effective for this project. This was because these would yield a comparable
propulsive force to four smaller units. Also, with two Rotor Sails, one on the
bow and one on the stern, there would be no chance of wind shadows affecting
performance.”

The Rotor
Sails were chosen for this project because they are easy to use, safe,
reasonably quiet, with no need for extra crew, and cheaper in investment
compared to other systems. In addition, the effectiveness of Rotor Sails has
been successfully proven.

“The effectiveness of rotor sails has been successfully proven”

The subject
of the main engines of the FF8500 has yet to be decided upon. “Switijnk has a
well-defined vision of sustainable shipping and we are glad to sit down and
share our knowledge with them. We have an extensive track record of integrating
mission equipment, and we have looked at all the options available to help them
achieve their ambitions. We have reserved space for LNG engines; although this
will be dependent on LNG bunkering infrastructure along their sailing routes.”
Due to the dependence on trade winds, a 100 per cent sailing vessel without an
engine is not economically feasible within the commercial cargo transport
sector.

With the
concept design of the vessel complete, the next stage of the project will
consist of testing at Maritime Research Institute Netherlands (MARIN). The
intention of this velocity prediction research is to validate the design and to
quantify the fuel savings to be gained. “Once investors are convinced and the
financing is arranged, then Switijnk can continue with the process of selecting
a shipyard to build the vessel,” Grijpstra adds.

This article was previously published in Maritime Holland magazine, issue 1, 2018