In this paper, we present a study on the energy-saving devices which is probably called Rudder-Bulb-Fin systems, designed for KVLCC2 tanker. The addition of horizontal fins which is installed on rudder for both sides can significantly reduce drag force in some applications. Several simulating cases of fin such as adjusting the angle of attack of fins, twisted fin, location of fins on rudder or even cutting starboard side fin have been designed and simulated using CFDSHIP-Iowa V4.5 code. The simulation results for those cases are validated by experiment; which are conducted in towing tank of Osaka University with fully loaded conditions at Froude number of 0.142. The flow field is measured in calm water using stereo particle image velocimetry at the downstream. The CFD and experimental fluid dynamics results showed a good agreement with the same test conditions. The total resistance by this design could be reduced a significant percentage amount and improved the propulsive efficiency by comparing with previous designs.