Minecraft wiki entry for Piston_uses, associated text: A dry dock can be made by reversing a Floodgate: instead of controlling the liquid, the player is controlling a solid. Place a piston facing upward in a 1 block deep pool of water and wire this piston to a lever. When a boat comes over the piston, flip the lever to raise the boat out of the water. This prevents the boat from being influenced by currents or being bumped.