In October 2020, the roro-vessel SC Connector will be retrofitted with two Rotor Sails and a battery pack. The installation will take place at JVP Steel in Poland. On leaving the yard, SC Connector will be a hybrid sailing vessel, and with good wind conditions she will maintain her service speed by sail alone. With rotor sails installed, SC Connector will be the tallest sailing vessel in Norway, soaring eight metres taller than the famous old Bergen tall ship, Statsraad Lehmkuhl.
With a growing international focus on reducing CO2 emissions and other gases/particles, the ability to harness wind to generate energy, reduce fuel consumption and emissions is a natural next step for the maritime transport industry.
The sails are designed as 35-metres tall and 5-metres wide cylinders. The Norsepower rotor sail is a modernised version of the Flettner rotor; a rotating cylinder that uses the Magnus effect to produce propulsion from wind (see next page). With the battery pack from Norwegian Electric Systems, SC Connector can avoid the use of auxiliary engines, which means that she can be 100% emissions free during sailings and at quay.
“By fitting rotor sails to SC Connector, we are utilising available renewable energy. The wind forces are used directly for propulsion, without the transformation losses associated with other energy carriers. As a sailing hybrid, we expect to reduce fuel consumption and CO2 emissions by 25 percent,” says Johan Christian Hvide, CTO at Seatrans.
Seatrans has a strong commitment to reducing the carbon footprint of their operations. “The goal for this project has been to design more environmentally friendly vessels by combining several existing technologies. In this case, we reduce emissions by 25 percent, which equals more than 1 million litres of diesel fuel annually. In addition to lower emissions, the project is customised for a future smart grid and prepared for shore power. The project has received funds from Enova, thanks to its environmental profile,” says Ole Sævild, Managing Director, Sea-Cargo.
“Currently, Sea-Cargo has major long- term agreements with the Norwegian export industry; including Hydro Aluminium, Boliden and others. This project will contribute to reducing the carbon footprint of these companies and will make both Norwegian short distance sea transport and Norwegian industry more environmentally friendly, thereby strengthening their position internationally,” Ole Sævild concludes.
“When we consider wind power, the aim is to catch as much wind as possible, and bigger sails catch more wind. The first Rotor Sails we looked at from Norsepower where much smaller, similar to previous installations on other vessels. After analysis, we asked Norsepower how big they could make their sails.
Due to transportation from the factory to the shipyard, the largest sail they can produce is 35 metres long and 5 metres wide. The two Rotor Sails for SC Connector will be the largest Norsepower has delivered to date,” Hvide continues.
Sailing service speed
In transit, the main combustion engine onboard SC Connector delivers all the power required for the propeller and ship systems. From calculations, we know that SC Connector’s propeller produces approximately 367 kN of thrust at 13.7 knots. As the wind speed increases, more thrust is generated by the rotor sail, relieving the main engine.
However, you cannot count on perfect wind conditions every time you cross the sea. SC Connector operates in the North Sea, which has some of the most favourable wind conditions in the world. With no wind, there will be no contribution from the sails. In stormy conditions, however, the vessel will need no other propulsion power. Similarly, with head winds there will be no contribution from the sails, while side winds will give maximum utilisation. With gale-force winds and a favourable heading, the vessel will maintain service speed on sails alone.
Combined with a battery pack from Norwegian Electric Systems, SC Connector can avoid the use of auxiliary engines, which means that she can be 100 percent emissions free during sailings and at quay
First in the world
Sea-Cargo has developed a new and unique technology that allows the sails to be raised and lowered while sailing. This tilt feature is designed for the extreme conditions in the North Sea, and allows the vessel to sail under bridges, overhead powerlines and into port. “By using hydraulics, we can lower the two sails in five to ten minutes with the push of a button on the bridge. When the sails are lowered, they will be the same height as the top lantern on SC Connector,” Hvide explains.
The visible, rotating parts of the Rotor Sails are made in Poland, using a light and strong composite material.
The rest of the structure is made from high tensile steel. Each rotor sails weigh in at 59 tonnes and will be mounted on a foundation structure that adds another 100 tonnes to ensure that the forces generated by the sails are absorbed by the vessel. The foundation structure elevates the rotor sail to a clear height of 7 metres above the weather deck. This is to avoid any impact to the vessel’s cargo capacity and operations.
Three hydraulic cylinders providing over 200 tonnes of pulling force raise and lower the rotor sails. This ensures that the system is redundant and can operate even in the harsh conditions in the North Sea.
Lessons learned from the sea
The maximum speed for the Rotor Sails is 180 RPM. That is a high speed for such a huge mass. The rotation is generated
by electric motors, and wind sensors will feed a computer which automatically calculates the optimal RPM to move the vessel forward with minimum or no use of the main engine.
The installation onboard will take place in October. “We are really keen on getting this project completed. We still have very much to learn, but we are convinced that it will be a profitable investment,”
Johan Christian Hvide concludes.
The Magnus effect
Anton Flettner was on a beach with his wife when he realised the potential of generating forces from rotating bodies. He used sand, flowing over his rotating hand to describe the Magnus effect. But can this force help move a vessel forward? The story starts with Isaac Newton in 1672 and his third law. He described the forces in his third law after observing tennis players at his Cambridge college. However, it was the German physicist Henrich Gustav Magnus (1802-1870) who investigated this in detail.
Think of a football game. You are the goalkeeper and your contribution to the team is to keep the ball out of the net. You are aware of a ball coming from around 20 metres out on the pitch. You automatically calculate where the ball will arrive, and you take your position based on that assumption. But, no. Suddenly the ball changes direction. It passes you half a metre on your right- hand side. Why? Most probably because the player who kicked the ball managed to give the ball an additional movement. As he kicked it forwards, he also made the ball turn around its own axis.
The result is that the ball moves slightly to the left (to your right). This is described as the “Magnus effect”.
Rotor ships use mast-like cylinders, called Flettner rotors, for propulsion. These are mounted vertically on the ship’s deck. When the wind blows from the side, the Magnus effect creates a forward thrust. Thus, as with any sailing ship, a rotor ship can only move forward when there is a wind blowing. However, when the Flettner rotors turns around its own axis (withan electric engine), the forces from the Magnus effect will provide propulsion for the vessel.
Today, the Flettner rotor sails are a supplementary propulsion system for transport vessels. Albert Einstein praised the Flettner rotor ship for its great practical importance. I wonder what he would have said about the modern-day Seatrans/Sea-Cargo version with its improved technology…