A vessel’s resistance when moving through the water is made up of multiple components, of which frictional resistance is the most dominant. Injection of air into the turbulent boundary layer (between the stationary and moving water) can reduce the frictional resistance of the hull.
Outlined below are the main technologies tested in full scale:
ALS - Air Lubrication Systems: Unlike the below mentioned ACS method that attempts to maintain air in fixed compartments, Air Lubrication Systems (ALS) provide a constant flow of air bubbles to lubricate the flat bottom area of a ship’s hull which requires minimal structural changes. The main technologies currently available in the industry are:
ACS – Air Cavity Ships: This method used large ‘cavities’ into the bottom of the hull filled with air. Full scale testing on the ‘ACS Demonstrator,’ an 83m multi-purpose vessel was executed by DK Group in 2008. The tests showed that in calm water, friction was reduced, but, in waves the energy needed to refill the cavities eliminated the overall savings. In conclusion, the associated significant structural modifications to the hull and cost rendered the idea impractical.
WAIP – Winged Air Inject Pipe: This concept involved 124 circular nozzles placed at the forward end of the hull expecting to lubricate both the flat bottom and vertical sides. The system was fitted to container carrier ‘Olivia Maersk’ in 2009 but after intensive testing, Maersk found that the balance between the energy and savings achieved was negative and the project was discontinued.
ACES – Air Chamber Energy Savings (similar to ACS): Developed as part of a series of Dutch national research projects with Damen Shipyards and MARIN. The system involved injecting air into large recesses covering the flat bottom of a vessel which claimed potential net power savings in calm water.
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