The authors verified an energy saving effect of an air lubrication system for the domestic service ferry which was one of slender body ships. The energy saving effect was evaluated by the engine output reduction rate of system ON and OFF at speed-trial test. As the result, a net energy saving effect of about 3.7% was confirmed.

After that, long-term voyage monitoring had been conducted since the ship was in service. At the same time, monitoring had been conducted about same type of sister ship without air lubrication system, in service on the same route.

The investigation result of the energy saving effect by comparison of fuel consumption of both ships, a net effect of about 3.13% was confirmed. According to these results, the effectiveness of an air lubrication system for slender body ships was proved; therefore, scope of an air lubrication system as energy saving system of ships had expanded.