Tests on Viking Grace confirm rotor sail’s fuel saving potential

Finland’s Norsepower Oy Ltd. reports that the rotor sail installed on the Viking Line cruise ferry Viking Grace has the potential to deliver annual savings of around 300 tonnes of LNG fuel.

The LNG fueled Viking Grace was retrofitted with a 24 m high, 4 m diameter Norsepower rotor sail a little over a year ago (see earlier story). The sail is a modernized version of the Flettner rotor; a spinning cylinder that uses the Magnus effect to harness wind power to propel a ship.

Norsepower says that when looking at fuel consumption alone over the measurement period, the fuel savings made by Viking Grace were not immediately evident. However, when expert analysis companies NAPA and ABB reviewed the data, they were able to isolate an evident change in the propulsion power breakdown of Viking Grace, caused by the rotor sail. The same conclusion was confirmed with a strain gauge analysis, where forward thrust of the rotor sail was measured and converted into propulsion power.

Based on the different analyses, says Norsepower, the expected long-term change in Viking Grace’s annual fuel consumption due to the rotor sail has been verified to be between 231 and 315 tonnes on annual basis, equatng to an average propulsion power between 207 kW and 282 kW. According to the analysis results, the rotor sail delivers more forward thrust on the open sea legs of the route for the Viking Grace, but due to the route being located mostly in the archipelago, the annual fuel savings potential is on the same level within both route areas.

As a result, Viking Line and Norsepower have agreed to continue collaboratively using and optimizing the rotor sail on the M/S Viking Grace with the technology now fully operational.

Tuomas Riski, CEO, Norsepower, commented: “When the test period began, we had some challenges with our new product, but were able to fix them quickly, and since the end of September 2018, the technical availability of the rotor sail has been around 97%. We are pleased to see that independent testing from respected, independent companies NAPA and ABB has shown impressive fuel savings potential on the M/S Viking Grace. This project has confirmed, that our technology works also with high-speed cruise ferries and that favorable results can be achieved with a service speed of 21 knots.

“During the last year we have been using the rotor sails in extreme weather conditions including icing events and high wind speeds, in which the rotor sail has been operational. based on the harsh weather experiences so far, the rotor sail can be operated around the year without any weather-related issues.”

Commenting on the trials, Jan Hanses, CEO, Viking Line said: “Viking Line has been testing the Rotor Sail on M/S Viking Grace for a year now, and together with Norsepower we will continue testing and optimizing the sail for its current route. We are proud to be the first in the world to trial Norsepower’s world-class mechanical rotor sail solution on a cruise ferry.”

“This analysis showcases the importance of onboard data collection and the value of ABB’s analytical services. Besides optimizing operations through improved energy efficiency on board Viking Grace, the data collected by ABB Ability Marine Advisory System OCTOPUS was used to calculate the savings gained from the rotor sail without disturbing operations,” said Marcus Högblom, Head of Passenger Vessel segment at ABB Marine & Ports.

Jaakko Talonen, Data Scientist, NAPA said: “In the actual navigational conditions there is always variation in the environment, which has an important effect on the fuel consumption. This is why a statistical regression model was applied, to overcome the variations in the comparison conditions and to disclose the effect of the rotor sail. The long history of NAPA on ship performance modelling gave a really good basis for the study.”