This invention captures hydrokinetic energy to do work such as produce electricity. The hydrokinetic flow exerts a torque on a turbine wheel. The wheel causes a set of tanks to rotate around a horizontal centerline. Working fluid drains from tanks near the top of the wheel to drive a conventional turbine before draining into lower tanks. Although a mechanical power transmission driven by the turbine wheel is simpler in concept, scale up to large slowly rotating wheels encounters increasingly difficult design problems: transmission of 1 kW at 1 rpm requires 6,959 ft-lb. In contrast, the conventional turbine of the fluid drive system provides mechanical power for use at a much higher speed than the turbine wheel. Therefore, very large engines can be built without a step-up transmission or components that must withstand extremely large torque loads. One unit can produce reliable 24/7 utility-scale base-load electrical power.