According to typical inventive practice, a cylindrical or prolate spheroidal marine hull has two congruent contra-rotative propellers coaxially situated at or near its axial ends. Each propeller has plural blades mechanically and/or flexibly attributed with changeability of blade pitch angles and blade flap angles. A blade-pitch control system adjusts the individual blade pitch angles of both propellers. The blade-pitch control system may be electronically and/or mechanically actuated, and is capable of: (i) cyclically adjusting the blade pitch angles of the two propellers so as to select two respective blade-tip-path planes, each characterized by a direction of thrust that is associated with the blade flap angles and is generally perpendicular to the blade-tip-path plane; (ii) collectively adjusting the blade pitch angles of the two propellers so as to select two respective magnitudes of thrust. The cyclic and collective blade commands, algorithmically coordinated, determine the direction, orientation, and speed of the hull.
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