an upper pontoon;

a lower pontoon;

a pylon structure extending between and interconnecting the upper pontoon and the lower pontoon; and

a single propeller assembly with a plurality of blades being rotatably coupled to the lower pontoon and configured to be rotated by a force from an underwater ocean stream flowing along the lower pontoon and past the single propeller assembly,

wherein the upper pontoon applies a vertical buoyant force on the lower pontoon, wherein rotation of the single propeller assembly generates electricity via a generator in the lower pontoon, and wherein the upper pontoon is configured to automatically generate a counter moment in an opposite direction to a moment generated by the rotation of the single propeller assembly to inhibit a roll motion of the underwater turbine system about an axis of the lower pontoon and configured to facilitate alignment of the lower pontoon with the underwater ocean stream flowing along the lower pontoon and past the single propeller assembly,

wherein the lower pontoon comprises a shaft operatively coupled to the single propeller assembly and to the generator, wherein rotation of the single propeller assembly by the underwater ocean stream rotates the shaft, which rotates a rotor relative to a stator of the generator to generate electricity, and

wherein the lower pontoon further comprises an electric motor coupled to a second shaft, which in turn is coupled to a friction winch assembly, the friction winch assembly comprises a plurality of pulleys about which a cable at least partially winds, the friction winch assembly being operable to shorten or lengthen a length of the cable that extends between the lower pontoon and a mooring weight to vertically lower or raise the underwater turbine system, the mooring weight configured to anchor the underwater turbine system to a sea floor.