Norsepower – sailing to a new age

Materials World magazine
1 Jun 2018

Jarkko Väinämö, CTO at Norsepower Oy Ltd, analyses the role that sandwich composites can play in wind propulsion and in efforts to decarbonise the maritime industry.

According to the third International Maritime Organisation (IMO) Greenhouse Gas Study, maritime transport emits approximately 1,000 million tonnes of CO2 annually, and is responsible for circa 2.5% of global greenhouse gas emissions. 

Those figures underline how fundamental the shipping industry is to global decarbonisation efforts, and there are plans in place, approved in April 2018 by the IMO, for a 50% reduction in these emissions by 2050. As such, shipowners and operators are turning their attention to clean technologies such as wind-assisted propulsion.

This technology relies on devices such as wingsails, soft sails, kites, or Flettner rotors, to capture the energy of the wind and generate forward thrust. Today, the number of commercial demonstration vessels remains minimal, however, this is set to change as more innovators trial wind propulsion technologies. 

The key to an effective emissions-saving system is in both the technology itself and the balance between stability, generated thrust, and the additional weight added to vessels. Manufacturing such technologies with materials that have the right attributes is, therefore, pivotal.

Out with the old, in with the new

The basic design of the Flettner rotor has been around for over 90 years, when German engineer Anton Flettner attempted to use the Magnus effect to harness wind power to propel a ship. 

The Magnus effect is named after the German physicist and chemist H.G. Magnus. When wind meets a rapidly spinning cylinder or sphere moving through air or another fluid (liquid or gas), the airflow accelerates on one side and decelerates on the opposite side. The difference in the speed of air flow results in difference of pressure, which creates a perpendicular force to the wind flow direction, propelling a vessel. 

Using this principle, large-scale cylindrical Flettner rotors were developed for use on ships as early as 1924. However, these were one-off projects and failed to capture the potential of the wider market. One of the reasons is the use of metals for the key structures. The weight of these materials meant that significant power was needed to spin them, they were easily dented, disrupting the balance of the system, and suffered from corrosion, resulting in significant maintenance requirements.  

Norsepower’s Rotor Sail Solution uses the same Flettner rotor technology to capture the energy of the wind and produce forward thrust through the foundation of the rotor sail. However, by working with Finnish naval architect, Kai Levander, new methods and new materials have been applied to the physics behind Flettner rotors.

Lightweight and fast

During initial testing, the rotor sails were produced using steel or aluminium, but composite materials were gradually introduced to some parts of the design due to the superior durability and static strength they demonstrated. In addition, the composite materials are lightweight, enabling the rotors to be rotated at the very fast speeds required with lower power consumption. When operational, the average surface speed is more than 100km/h and the maximum surface speed is close to 170km/h.

The load carrying structure – also referred to as the inner stationary tower – is made of steel, while the outer rotating rotor consists of lightweight composite materials made of carbon fibre and glass fibre reinforced plastics. 

In addition, the sails are controlled by software, activated with a push-button start. This creates a fully automated system that senses when the wind is strong enough to deliver fuel savings, at which point the rotors start automatically. Overall, it represents a reimaging of the Flettner rotor for 21st century ships. 

Despite using lightweight composites, the sails remain significant structures aboard a ship. The weight, with a typical foundation included, varies from 20 to 50 tonnes. On a ship where stability, balance, the ability to withstand the elements, and the integrity of the deck and relevant connections are critical, safety remains of paramount importance. As such, the sails have to go through land-based testing, including of mechanical and performance properties, to ensure their safety and effectiveness over a range of wind conditions and speeds. 

Out to sea

Part of the testing also includes sea trials, which the first prototype underwent in November 2014 onboard the Finnish shipowner Bore’s 9,700 deadweight tonne, cargo ship M/V Estraden. Following data analysis by data analysis, software and services provider, NAPA, which suggested that greater fuel savings were possible, a second rotor sail was installed in 2015. 

Today, the vessel sails its normal route between Teesport, UK, and Rotterdam, the Netherlands, with two of Norsepower’s smaller rotor sails. This wind-assisted propulsion has reduced fuel consumption by 6.1% – approximately 400 tonnes per year in and roughly US$246,800 per year in fuel costs, based upon the Rotterdam April 2018 MGO price. 

With the data collected from the M/V Estraden, up to 20% average fuel savings per year could be achieved on routes with favourable wind flows, sufficient sized rotor sails, and speeds.

The rotor sail can be used with new vessels or retrofitted on existing ships, and is particularly suited to passenger ships, such as cruise ships and ferries, and those transporting goods in bulk, for example tankers and bulk cargo carriers. The main requirements for installation are deck space and electrical connections to the ship. 

Typically, the foundations can be welded on the deck without changing the internal structure. The sails are then installed on the foundations with a bolt connection. After which the rotors can be lifted onto the vessel and attached to the foundations – either during a yard stay or port call. The sails are available in three sizes with heights of 18m, 24m, or 30m, and corresponding rotor diameters of 3m, 4m, or 5m.

Condition monitoring data is also collected via a cloud-based system, and supplemented with a ship’s data, to monitor how the sails are operating in real time, including the drives, bearings, and structure, to help plan preventative maintenance.

In April 2018, the liquefied natural gas (LNG)-fuelled M/S Viking Grace, became the first passenger ship to use auxiliary wind propulsion. With the addition of a 24m high, 4m diameter Norsepower rotor sail, the vessel hopes to reduce its carbon emissions by circa 900 tonnes annually, equivalent to cutting 300 tonnes of LNG fuel per year. Viking Line has also announced plans for a newbuild cruise ferry vessel that will also use rotor sails.

In addition, Norsepower is supplying two 30m tall by 5m diameter systems to be retrofitted onboard a Maersk Tankers ship. These are expected to reduce average fuel consumption on typical global shipping routes by 7-10%.

The new age of sail

These predictions are based on several measurements, including fuel consumption, CO2 emissions reductions, and how the physical components are performing. In addition, weather data is collated to better understand how the system behaves and reacts to varying environmental conditions.

To meet the goal of reducing maritime emissions by 50% by 2050, significant changes are needed to the fuelling, propulsion systems, and technologies onboard ships. Wind-assisted propulsion, empowered by materials technology and the development of advanced sandwich composites, is one of the potential pathways to achieving this. 

In fact, if applied to the 20,000 applicable vessels currently in operation, it is estimated that rotor sails alone could contribute a 5% reduction in total industry emissions. It’s time to usher in shipping’s next golden age of sail – this time, one that is built on carbon fibre, rather than canvas.