A sea thermal power plant is provided with pumps of the propeller type for bringing up cold water and forcing it through suitable condensers or heat exchangers and for drawing a continuous flow of warm water from a surface layer of the sea and forcing it down through suitable heat exchangers or boilers of the plant. The water so drawn from the sea flows through the heat exchangers and is subsequently discharged therefrom, which action creates thrust thereby producing forces to move the plant over the water surface. The heat exchangers are provided with deflectors which control the direction of discharge to produce a reaction force in any desired direction to drive the power plant. The pumps have associated therewith pipes which have located therein, downstream of the pumps, bypass louvres or vanes which can be opened to discharge water directly into the sea to produce a higher thrust for moving or positioning the power plant.