The recent rush towards application of energy saving devices caused by increased demands on ship efficiency lead to installation of ESD on a wide variety of ship types. The evaluation of performance is still to a large extent based solely on the towing tank measurements while the experience in full scale gathered from sea trials is scarce.

The significant differences in boundary layer development and wake field at the propeller position between model and full scale are often not taken into account in the ESD design. Therefore, the gains in required power are often severely overestimated. In the present work SHIPFLOW CFD code is used to evaluate power requirement changes in model and full scale conditions for a selected energy saving device. The stern flow determining the propeller working condition is analysed. The evaluation is performed using both the resistance and the self propulsion simulations for better understanding of the scale effects.