Abstract: A cracking device for use in a dredger includes a housing body having an elongated cavity receiving an elongated piston and a hammer rod to be struck by the piston. The cavity forms a gas chamber around a top end of the piston for receiving an operating gas, an annular hydraulic chamber around the piston adjacent to the annular flange, and an impact chamber around a bottom end of the piston and around a top end of the hammer rod. The hydraulic chamber is divided into two variable volume upper and lower chambers by an annular flange of the piston. A passage is provided in the body to permit a hydraulic fluid to operate in the hydraulic chamber through the passage. A hydraulically operated control valve is connected to the passage and the hydraulic chamber for controlling the operation of the hydraulic fluid.