A ship which has been modified to facilitate drilling down through the center of the ship. These units are usually self-propelled and are vessels. A dock in which a vessel can lie out of the water while repairs are being made below its waterline. It looks like a shoe box with the top and ends removed. The bottom and sides contain compartments.
Water enters the compartments causing the dock to sink low enough to allow a ship to enter.
Pumps then suck the water out and the dock rises, lifting the ship out of the water. Floating dry docks are vessels. One end of the dock opens into a waterway. When a ship enters the dock, a floating gate is placed against the open end. A structure which allows the hoisting of a ship from the water to an elevation above the highest tides, where it rests on a structure fixed to the ground.