Ships fitted with bubble-blowers in emissions experiment

Japanese firms NYK and Mitsubishi Heavy Industries are testing an air-lubrication system to reduce CO2 emissions during marine transport.

Jointly developed by the two companies, the system effectively reduces the frictional resistance between a vessel's bottom and the seawater by generating a stream of air bubbles under the vessel. The first permanent installation of the system using an air-blower is expected to reduce CO2 emissions by approximately 10 per cent.

The experiments will be conducted using module carriers operated by NYK-Hinode Line.

A module carrier is a heavy-load carrier with roll-on, roll-off rampway, built to transport thousand-ton prefabricated structures for oil and gas installations or industrial facilities.

Construction of the vessels at MHI's Nagasaki Shipyard will be completed on 31 March and in late November 2010.

Module carriers were chosen because this type of vessel has a wide, shallow-draft hull that generates relatively little water pressure and so minimises the electrical energy required by an air blower to supply air to the vessel's bottom. Moreover, its shape means that supplied air is expected to be readily retained under the vessel's bottom.

The object of the experiments is to verify fuel-reduction effects, verify the behaviour of the air bubbles under various operational and sea conditions, verify the relationship between the amount of air supplied and its effects and demonstrate CO2-reduction effects.

Japan's Ministry of Land, Infrastructure, Transport and Tourism is subsidising the project, with additional support from ClassNK and the Nippon Foundation.

Bubble layers have previously been used to reduce friction on small boats, as have anti-friction coatings, but these are more effective on faster vessels than for general shipping.

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