New spin on old technology for big ships

 By RP Siegel

When man first began harnessing the wind, it was to power boats cruising the river Nile, some 7,000 years ago. From there, it went to work pumping water, and then, more recently, for generating electricity, which has grown to provide substantial generation capacity in many areas. The use of wind for moving ships, on the other hand, has been relegated to the world of recreational sailing—or has it?

Not so fast. It turns out that wind can still play a role in powering large-scale commercial ships, without compromising speed, reliability or safety, while significantly reducing fuel costs and emissions. The idea is being put into practice by the Finnish company Norsepower. In this updated, modern approach, the traditional sweeping masted canvas sails have been replaced by spinning composite cylinders known as rotor sails, which take advantage of a principal called the Magnus effect. The net result is much the same as those clipper ships of old, which is to say that varying pressure on opposing sides of an object can cause lift, but with a high-tech twist.

Sketch of Magnus effect with streamlines and turbulent wake (Rdurkacz, Wikimedia)

We spoke with Jukka Kuuskoski, SVP, Sales and Marketing at Norsepower, about this innovative approach to maritime transport. He explained that the spinning cylindrical sail is an application of the Flettner rotor, invented by the German engineer, Anton Flettner, back in 1922. Flettner tried to commercialize his invention back then, but was unsuccessful, despite demonstrating the idea with a prototype that crossed the Atlantic without incident.
Norsepower’s Rotor Sails, which range from 3 to 5 meters in diameter and are 18 to 30 meters tall, are rotated by electric motors. The thrust they produce is lift, much like in an airplane wing. That lift actually pulls the ship forward by producing a low-pressure region in front of the sail, when the wind comes from a suitable direction. The efficiency with which this thrust is developed, depends on maintaining the rotational speed of the rotor in relation to the apparent wind impinging upon it, which is constantly changing.
The reason that the idea is far more viable now, explains Kuuskoski, is that modern, computerized control systems can continuously adjust the rotor speed to meet the precise, optimal conditions, something that was simply not achievable in Flettner’s day. With this enhanced control, a rotor sail can provide thrust equivalent to that of a traditional fabric sail ten times its size.
Norsepower’s first installation took place in 2014 on the cargo ship M/V Estraden, which is owned by Bore Ltd. It included a 18 x 3 meter rotor sail, to which, a second was added later. Together, the two sails saved 400 metric tons of fuel and eliminated 1,200 metric tons of carbon emissions over a year of operation, numbers that were third- party verified by NAPA, the leading maritime data analysis, software and services provider.

Norsepower Rotor Sail Solution

According to Norsepower, the addition of one or more of these sails, can allow the main engines to throttle back, providing as much as 20 percent energy savings. The company has developed simulation software that can estimate the savings achievable for every ship, which depends on both the ship’s characteristics, as well as the prevailing winds along the routes that each trip is expected to travel. Many ships run the same route, day after day, which makes it relatively easy to estimate projected savings. Based on these types of analyses, Kuuskoski estimates that as many as 20 percent of the roughly 100,000 commercial ships plying the seas could see benefits from adding rotor sails.
A number of additional ships have contracted for Norsepower’s Rotor Sails, ranging from passenger ships, such as the Viking Grace, to a long-range tanker owned by Maersk. These are expected to be fitted in 2018.
Other companies offering rotor sails for ships include Magnuss and Thiiink.

SEE MORE: Naval uses for cleaner fuel by Peter Ward

about the author
RP Siegel
Skilled writer. Technology, sustainability, engineering, energy, renewables, solar, wind, poverty, water, food. Studied both English Lit.and Engineering at university level. Inventor.