The watercraft described herein is a surfboard, skim board, dive board, or boat having a propelling fin driven by a standing surfer or boater with an upward and downward stroke which may be used to propel the watercraft by an upward and downward fin motion. The surfboard and dive board in particular are used on water and may be used to ride ocean swells and waves. The surfer or diver stands on the board and moves a vertical handle upwardly and down-ward. The lower end of this handle is pivotally attached to a parallel bar device having attachment means to the board at a forward end of the parallel bar device and having attachment means to a fin at the aft ward end of the parallel bar device. The fin is generally horizontal and is driven thru the water up and downwardly by the standing user and propels the board forward at higher rates of speed than can be achieved by prone-paddling. The handle, four bar device, and fin may be stowed within the body of the board when in a non-propelling position and so allow the surfer or diver to lie upon and paddle the board in standard surfboard prone paddling fashion while also enabling the board to be ridden as a standard surfboard upon the ocean waves.