Abstract: The mechanism comprises, in combination, a main power shaft, a propeller shaft, a housing for the propeller shaft, a disc-type constant velocity joint (Rzeppa joint) operatively connecting the main power shaft and the propeller shaft, and a tillar arm operatively connected to the housing of the propeller shaft. The Rzeppa joint enables the axial angular displacemnt of the propeller shaft relative to the power shaft to be altered in all directions. Thus if the boat encounters a submerged obstacle, the propeller shaft and its housing can automatically ride over the obstacle and avoid damage or entanglement. Preferably the system also includes a latch and stop assembly that enables the operator to pre-set the vertical angular displacement of the propeller shaft relative to the power shaft in various positions, e.g., (1) uplock (for overland transport and starting). (2) shallow drive (for travelling through swamps where the water is only a few inches deep).