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A graving dock is a channel-like dry dock with a watertight caisson gate. To dock a ship, the graving dock, is flooded to normal sea or river level and the gate opened for the ship to go in. The caisson gate is closed back and the water pumped out until the dock is completely dry.
Whereas, a floating dock is a barge-like floating structure with wing walls on port and starboard and port sides. It has pontoons below the work-deck which are flooded to sink the floating dock to the required draft. The vessel to be docked comes in between the two walls and well secured. the dock floats up by pumping out the ballast water from the pontoons until the vessel is completely out of the water.
Graving Dock: This is a dock built by excavating a large portion of the sea side and at the sea side end there provides a dock gate; this is the most common form of dry dock.
Floating Dock: This is a pontoon with length and width suitable for accommodating a specific size of ship. The pontoon is immersed into the sea deeper than the ship's draft, and the ship is transferred to the pontoon; the ballast in the pontoon is discharged so that the pontoon rises to the surface together with the ship on the pontoon.
