Bubble surfing brings savings
Ships cut fuel use and pollution by using the same techniques that help penguins swim quickly.
Penguins release streams of lubricating bubbles from their feathers to help them surge out of the sea.
Now shipping engineers and operators are looking for similar ways to reduce friction between ships and sea water, with a system that releases air to create a carpet of bubbles along the bottom of the ship.
“This technology could improve ship energy efficiency by more than 5%,” says David Connolly, Lead Principle Maritime Technologist at Shell. “That means less fuel used and less air pollution.”
Ships are the blood cells of global trade, carrying a vast range of goods, including food, fuel, technology and textiles. They transport around 90% of goods traded around the world.
Greenhouse gas emissions from shipping fell during the global economic slowdown. But the United Nations International Maritime Organization (IMO) believes that a rebound in global trade could lead to carbon dioxide emissions from the sector doubling by 2050 from their level in 2010.
The organisation has introduced mandatory energy efficiency targets, prompting ship users and owners to look for ways to save fuel and cut emissions.
Could emperor penguins have the answer? They have long exploited the efficiency benefits of bubbles. Scientists have observed the birds using air trapped in their plumage to produce streams of bubbles which help them swim quickly enough to rocket out of the sea onto the ice.
A growing number of marine technology companies are developing ships that also blow bubble streams from the bottom of their hulls. This helps improve efficiency because air produces far less fuel-sapping friction than sea water.
Shell, one of the biggest users of ships for transporting oil and liquefied natural gas around the world, has been testing a new air lubrication system developed by UK-based Silverstream Technologies. The technology has been fitted to an oil products tanker, owned by the Danish shipping company Dannebrog Rederi.
Shell’s direct involvement in the trial has ended, but it continues to study data collected by the bubble boat. Since setting sail with the new system in early 2014, the tanker has covered around 100,000 kilometres on voyages stretching from Europe to Asia and Latin America.
The trials so far show energy efficiency improved by an average of around 4%. Experts at Lloyd's Register, the engineering and technical consultancy, verified the results. People working on the project believe they can achieve greater fuel and emissions reductions as they learn more about the optimal sailing speeds for the system.
The trial vessel was retrofitted with the system in a couple of weeks. It can also be installed in vessels while they are being built. The first commercial installation of the Silverstream® system on a new ship is expected to be on a Norwegian cruise liner due to be completed in early 2017.
Shell is considering fitting such technology to its own ships.
- The system automatically regulates the compressors depending on sailing speed.
- Compressors keep cavities near the front of the ship filled with pressurised air.
- Air is released from the cavities in streams of bubbles as the vessel moves through the water.
- The bubble streams emitted from each cavity merge into a single "air carpet" along the flat bottom of the hull.
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