Abstract: A readily retractable sonar sensor system having a sensor carried by a rod slidably mounted in a sleeve which is located in spaced relation to the axis of rotation of a disc upon which the sleeve is fixedly supported, the latter extending normally to the radius of the disc. The disc is pivotally mounted on a plate which is supported by a C-clamp connected to its peripheral portion and mounted on a boat transom. Spring means surrounding the pivot pin urges the disc and plate together, causing matching projections on the disc to extend into openings in the plate to releasably control relative rotation therebetween, so that when the rod is swung to generally horizontal orientation, the sensor swings rearwardly and upwardly out of the water.