Experimental Analysis of the Effect of Air-Injection Pressure System Configuration on the LNG Resistance

Abstract

Ballast-free systems (BFS) provide an ecological alternative to conventional ballast water systems but increase ship resistance due to additional wetted surfaces and discharge outlets. Limited studies have experimentally quantified the drag reduction potential of air lubrication in BFS configurations for LNG vessels. This study investigates the integration of air-injection pressure systems to mitigate this resistance penalty. Experimental tests were conducted on a 1:80 scale model of an LNG vessel, evaluating various configurations of air injection at 0.5 bar and water pump operation. The results show that while BFS alone increased total resistance by an average of 2.67%, the optimized configuration BFS+0.5B+B_Config—which combines air injection from all water ballast tanks (WBTs) with water pumping only to the fore WBTs—effectively counteracted this effect. This configuration achieved an average resistance reduction of 4.6%, peaking at 6.81% at a Froude number of 0.19. These findings validate the practical integration of air lubrication in BFS-equipped LNG vessels, offering a pathway to enhanced hydrodynamic efficiency and improved environmental sustainability in maritime transport.