Abstract: A device for restraining the upward movement of a dock comprising a hydraulic cylinder having a fixed end; a piston slideably disposed in the cylinder so as to define opposed first and second chambers; a rod having one end connected to the slideable piston, extending through the first chamber and having another end adapted for connection to the dock; hydraulic reservoir containing hydraulic fluid communicating with the first chamber; valve means disposed between the reservoir and the first chamber, the valve means having open position permitting the hydraulic fluid to flow from the first chamber to the reservoir and extending the rod in response to the upward movement of dock; a closed position stopping the flow of the hydraulic fluid from the first chamber to the reservoir and restraining the upward movement of the dock.