M/S Berlin gets a new rotor sail: Ingeniøren observes the process

30. maj 2022 kl. 11:05
M/S Berlin gets a new rotor sail: Ingeniøren observes the process
It took about an hour for the engineers and technicians to carefully lift the rotor sail onto the M/S Berlin ferry. Illustration: Scandlines.
At the industrial port of Rostock, a ferry berth is ready to lift the 30-meter-long and 42-tonne rotor sail and put it into place.
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Quite slowly, the cylindrical tube is lifted into the air. A handful of men wearing yellow reflective vests and safety helmets rush around the port, attentively following every movement of the 42-tonne sail. Finally, the 30-meter-long cylinder reaches just the right height, and the crane operator can start the rotation so that the rotor sail can be put into place on the MS Berlin ferry.

With great care, the crane operator rotates the huge sail into place. An hour and a half had been set aside for the procedure, but it ended up taking just under an hour. Illustration: Benjamin Bøllehuus.

We are located in the large industrial port of Rostock, where Scandlines has rented a ferry berth for the occasion.

Scandlines is getting a rotor sail installed on one of two ferries that sail back and forth between Rostock and Gedser. In 2020, its sister ferry, M/S Copenhagen, had a rotor sail installed by the Finnish company Norsepower, and after collecting sufficient data and concluding that the fuel savings were satisfactory, it was decided that both ferries should have rotor sails.

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Tonight it is the M/S Berlin that is getting a rotor sail. Engineers and technicians from Norsepower are rushing around the quay, and as the sail after a little less than an hour of gentle travel hangs over the foundation, the engineers begin to prepare for the descent so that the sail can be securely fastened to the foundation.

From there, power is supplied to the sail, so that it can reach the necessary revolutions and enable the sail to operate at wind speeds of up to 25 m/s.

Norsepower employees are in the process of preparing for the installation of the rotor sail. The foundation on which they stand was installed as early as last autumn and will carry the 42-tonne sail. Illustration: Scandlines.

Rasmus Nielsen, naval architect at Scandlines, says that the biggest challenges in mounting a rotor sail on a ferry are transferring the forces from the rotor sail to the ship’s structure and ensuring rigidity in the foundation.

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“We had to mount four pillars down on the passenger deck to ensure sufficient rigidity in the foundation of the rotor sail,” he says.

“If the foundation is not rigid enough, resonance will lead to the rotor sail not being able to reach maximum revolutions.”

The two pillars next to the stairs have been mounted in connection with the installation of the rotor sail to ensure the stability of the ship. There are two more pillars 10 meters further down the hall. Illustration: Benjamin Bøllehuus.

The rotor is a composite material - in this case fiberglass. The foundation and tower inside the rotor are made of steel. The sail rotates constantly, even when not in use. In that case, it rotates only 10 times a minute, but that is to keep the bearings straight so they do not get damaged.

The sail has been lifted into place. The very next day, the ferry will return to its regular route, but the engineers need a few more days to retighten everything inside before the sail can be put into use. Illustration: Benjamin Bøllehuus.

At 5:55 PM the sail is carefully manoeuvred into place. Meanwhile, wind picked up speed, and the hair of those on board is gradually getting windblown. However, the wind does not affect the sail, which has steadily slid into place on the foundation, so the employees from Norsepower can start bolting the sail to the foundation.

Inside, the column is hollow. The video below shows the foundation to which the sail must be attached as well as the cables that will ensure power is supplied to the sail.

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The fully automatic system makes use of the Magnus effect

The concept behind the rotor sails, called the Magnus effect. Illustration: Norsepower.com.

On a day with favourable wind conditions, the sail can reduce CO2 emissions by up to 20 percent. On average, Scandlines expects a reduction of between four and five percent. The stretch between Gedser and Rostock is particularly suitable for rotor sails, as the wind is usually perpendicular to the ship’s sailing direction, which are optimal conditions for a rotor sail.

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In April, data from the rotor sail on M/S Copenhagen showed that the sail did not contribute to the propulsion on only a single day.

At the front is M/S Copenhagen, which has now been sailing with a rotor sail for more than a year, while in the background you can see M/S Berlin, which is having its sail installed. Illustration: Scandlines.

The rotor sail works by utilizing the Magnus effect, which occurs when the wind meets the rotor sail, which rotates about its own axis. The wind will decrease in speed on one side of the column, while it will increase on the other side. This creates a difference in pressure that gives the ship extra propulsion.

One of the requirements for the rotor sail is that it must not require any manpower, says Rasmus Nielsen, naval architect at Scandlines.

“The system is completely automatic, which was a requirement for us, so we don’t have to use crew to check up on the sail,” he says.

“With input from the wind direction and speed as well as the ship’s speed, the rotor sail continuously calculates the correct direction of rotation and speed, so that it operates as efficiently as possible.”

At the same time, the sail is also automatically switched off at geographically defined positions when the ferry comes close to the ports of Gedser and Rostock.

Scandlines will not say how much has been invested in the rotor sails, but Rasmus Nielsen says that the financial gain is directly related to fuel prices.

“We estimate that the sail can last the 25–30 years that the ship itself can last before it has to be scrapped,” he says.

Not the first of its kind

The idea of a rotor sail is almost 100 years old and was invented by the Finnish engineer Sigurd Savonius, while the German engineer Anton Flettner demonstrated the technology on a transatlantic sail in 1926—hence it is also sometimes called a Flettner sail.

The height varies depending on which ship it is to be installed on and is available in different sizes: 18, 24, 28, 30, or 35 meters. The sail is controlled via a simple control panel from the ship’s bridge, where the captain can activate and deactivate the sail.

A large 35-meter-high column can of course present its own challenges for certain ships when they have to sail under a bridge. However, Norsepower solved this issue last year by making a system that enables the rotor sails to be tilted to an almost horizontal position so that the ship can sail under a bridge.

The same solution does not apply to M/S Berlin’s rotor sails, and Scandlines also states that even with the 30 meter high rotor sail installed, the ferry can pass under the Great Belt Fixed Link when it goes to the shipyard.

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