Abstract: A paddle wheel transducer for mounting to a marine vehicle utilizes a source of radiant energy for establishing a beam of radiant energy directed perpendicular to the direction of movement of the paddle wheel vanes and a radiant energy responsive element for detecting interruptions of the radiant energy beam produced by passage of the paddle wheel vanes therethrough to detect paddle wheel rotation. The radiant energy beam is a beam of infrared light and the radiant energy responsive means is a phototransistor.In providing a marine speedometer utilizing the radiant energy paddle wheel transducer, the phototransistor is connected in an electrical circuit which produces an electrical pulse output signal representative of paddle wheel rotation. The pulse signal is applied to digital circuitry which is operable to count pulses under the control of auxiliary control logic and develop a count representative of marine vehicle speed. The marine vehicle speed is displayed on a digital readout.