A turbine comprises a shaft (20), a mass (10) eccentrically mounted for rotation about shaft (20), having its center of gravity at a distance from the shaft (20) and a motion base (15). Motion base (15) rigidly supports the shaft (20), and is configured for moving the shaft (20) in any direction of at least two degrees of movement freedom, except for heave.A floating vessel-turbine (120), encloses entirely the eccentrically rotating mass (10) and the motion base (15). The turbine converts ocean wave energy into useful energy, very efficiently.