Maersk is not convinced by the benefits of air lubrication. The box ship operator equipped the 3000 TEU, 240m-long Olivia Maersk with the system back in 2009. Work involved an elaborate air supply system delivering air through some 2km of piping to 124 outlets in the forward part of the underwater hull to a depth of about 10m. These create an air barrier that reduces friction.
"We couldn't verify the savings," Jasper Boessenkool, head of innovation and strategic R&D at the Danish operator revealed during Danish Shipping Days, a week long exposition of maritime conferences and other events recently held in Copenhagen. "While a promising technology, the exercise demonstrated the challenges of applying laboratory science at full scale in real world conditions," he observed.
The air lubrication concept originates from research in Japan. The idea is to use a relatively small amount of energy to compress air, and to generate micro bubbles through instability of the air-water interface at each opening in the hull. Friction exerted by the fluid should then be reduced, provided the bubbles stay within the boundary layer close to the hull.
One of the practical challenges, explained Boessenkool, was creating a stable layer of bubbles. But what proved the death knell at Mearsk was the difficulty in measuring the system's performance. "The decision to keep or ditch any new technology comes down to the overall energy balance. We tried sailing with the technology on and off but the results were inconclusive."
While air lubrication has been put on ice at Maersk, other companies are still exploring the concept, with efforts focusing on locating the holes exclusively on the flat bottom so that the bubbles last longer and don't immediately dissipate up the hull's side.