PURPOSE: To increase the propelling efficiency of a one-propeller one-shaft vessel, by providing windmill type water turbine blades whose diameter is smaller about a specific value than a propeller, and whose number is the same as the propeller blades or an integlar number times, by positioning the front edges of the blades between lines passing the rear edages of the propelled blades and parallel to the propeller shaft, and directing their positive and the negative pressure surfaces in the reverse direction of those of the propeller blades.

CONSTITUTION: A propeller member 2 has four sheets of propeller 22 around a boss 21, while a water motor 3 has four sheets of windmill type water turbine blades 32. Those windmill type water tuebine blades 32 have the diameter smaller about 10% than the diameter of the propeller member 2, and the number of the blades is the same or an integlar number times of the propeller blades 22. And the front edges of the windmill type water turbine blades 32 are positioned between two lines passing the rear edges of the propeller blades 22 and parallel to the propeller shaft 5. Furthermore, the positive and the negative pressure surfaces of them are directed in the reverse direction of the positive and the negative pressure surfaces of the propeller blades 22 of the propeller member 2. Consequently, the propelling efficiency of the one-propeller one-shaft vessel can be increased.