Full scale applications of air lubrication for reduction of ship frictional resistance

Abstract

Frictional resistance occupies a large portion of the total resistance of a vessel accounting for nearly 60 ∼ 80%, and lower friction resistance can lead to a remarkable reduction in greenhouse gas (GHG) emissions from ships. Air lubrication is widely recognized as one of the useful technologies to reduce a ship's frictional resistance by injecting air to cover a large portion of wetted hull surface. In present study, first, the effects of injected air layer on the skin frictional drag are investigated through various experiments and relevant analysis on a flat plate and model ships. Then, particular air lubrication systems for two full scale ships are designed, and their performance are validated by the data obtained during actual voyages. A heavy cargo carrier and an LNG carrier are selected for the full scale applications, whose results have been derived from a joint development project with the participation of a shipyard, ship owners and a certification body. The amount of fuel saving through the application of the air lubrication system is evaluated by analyzing operation data acquired during sea trials and actual voyages in service. The installed air lubrication system on the bottom of the ship hull is found to be effective for the reduction of the fuel oil consumption. The overall efficiency of the air lubrication system can be further improved by optimizing the size and location of the air injectors, which are deemed as the two important parameters for optimum design of the air lubrication system. This paper discusses the experience gained in applying the air lubrication technology to the full scale ships, and demonstrates the effectiveness of the air lubrication for reducing fuel consumption of ships on the actual seas. ？ 2017 The Society of Naval Architects and Marine Engineers. All rights reserved.