Norsepower's Rotor Sail solution on board Bore's mv Estraden
Bore has been looking into new technologies to help reduce the environmental footprint for a long time. In 2013 Bore contacted the start-up company Norsepower, a leading sail technology provider for commercial shipping, to look into the possibilities of using wind power to create thrust. Since then, Bore and Norsepower have conducted tests of Rotor Sails aboard mv Estraden.
Essentially a Rotor Sail follows the physics of the Magnus Effect, already discovered in the 1920s by Flettner (DE) and Savonius (FI). When wind meets a spinning object, a high and low pressure differential is created, which creates thrust at a 90° angle to the wind - see below illustrations.
In 2014 this project started with investigations and simulations of weather conditions of the last 10 years for areas in North West Europe. Initially, one rotor was tested on land at Turku Repair Yard, Finland for approximately three months and following excellent results the first rotor of 3 x 18 m was installed on board mv Estraden in late November 2014. The foundation for the rotor had been built into the vessel previously during her dry docking. The installation of the first rotor took only seven hours from start to a fully rotating rotor, and was done during a normal port stay. Two independent research bodies (VTT and NAPA) monitored the test period.
Additional sensors and equipment, such as a thrust meter, were installed and both thrust and thrust reverse tests were performed by rotating the rotor in different directions at different speeds. Data was collected, analysed and corrected to obtain comparable fuel consumption figures for reference over the trial period. The result of the trial period showed that while using the Rotor Sail, the net fuel consumption reduced by an average of 2.6%.Thrust production was in line with expectations and the input power was about 7% less than predicted. Mechanical construction was proven, system availability was 99%, noise and vibrations were on a low level and the control system was easy to operate and reliable.
The team also established that using the Rotor Sail in crosswinds results in a decrease in fuel consumption. As mv Estraden typically operates between Teesport in the UK and Zeebrugge in Belgium several times a week, the weather conditions were optimal, with a crosswind blowing about 85% of the time. Bore decided to install a second Rotor Sail on board mv Estraden, which was done a year later in November/December 2015. Since then, the Rotor Sails have been in service for around six years. The yearly net fuel savings are 4-5%, which means CO2 is reduced by about 1,000 tonnes per year. The Rotor Sails could be used 97% of the time and the lifetime of the equipment is expected to be approx. 20 years with only regular maintenance such as changing the bearings necessary. Deploying Rotor Sails for wind propulsion has proven to be a commercially viable renewable energy solution for the trading area where mv Estraden operates, which is subject to crosswinds for most of the year.