Energy saving devices are becoming to be generally equipped to ships. Stern duct is one of the devices, which has the ability to improve the propulsive performance with increasing the thrust deduction coefficient (1- t ) and decreasing wake coefficient (1- w ). The energy saving effect of the stern duct is usually evaluated by the tank test only in still water, because of the difficulty of analysis with the data obtained by the tank test in waves. The data would have a large amount of uncertainties compared to the one obtained in still water condition and also the implementation of the tank test in waves will be practically impossible because it takes too much cost and time. Thus it is a little known about the performance of a stern duct in waves.

Energy saving devices are becoming to be generally equipped to ships. Stern duct is one of the devices, which has the ability to improve the propulsive performance with increasing the thrust deduction coefficient (1- t ) and decreasing wake coefficient (1- w ). The energy saving effect of the stern duct is usually evaluated by the tank test only in still water, because of the difficulty of analysis with the data obtained by the tank test in waves. The data would have a large amount of uncertainties compared to the one obtained in still water condition and also the implementation of the tank test in waves will be practically impossible because it takes too much cost and time. Thus it is a little known about the performance of a stern duct in waves.