Asymmetric Stern Modifications for KVLCC2

Asymmetric modifications in the stern of KVLCC2 vessel are made in order to improve propulsion efficiency. The purpose of the modifications is to create a pre-swirl in a direction opposite to that of the propeller rotation and hence reduce losses. Stern asymmetry is designed by geometric modifications of the stern frames through an angle in the direction opposite to that of propeller rotation. The nominal wake distribution is investigated using CFD analyses along with the distribution of axial and tangential velocity components. A significant difference in the tangential velocity component is observed between the original symmetric KVLCC2 and the modified asymmetric case. The resistance of the asymmetric variant is found to be marginally higher. However, the rpm in self-propelled condition and the power requirement is found to be reduced by the asymmetric modification. For the asymmetric variant, model scale self-propulsion experiments indicate a reduction of power by about 8%, whereas full scale CFD calculations estimate a reduction of 4% corresponding to the design speed of 15.5 knots.