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A dry dock (sometimes drydock or dry-dock) is a narrow basin or vessel that can be flooded to allow a load to be floated in, then drained to allow that load to come to rest on a dry platform. Dry docks are used for the construction, maintenance, and repair of , , and other watercraft.
It has been calculated that a dock for a vessel of such a size might have had a volume of 750,000 of water.
Possibly the earliest description of a floating dock comes from a small Italian book printed in Venice in 1560, called Descrittione dell'artifitiosa machina. In the booklet, an unknown author asks for the privilege of using a new method for the salvaging of a grounded ship and then proceeds to describe and illustrate his approach. The included woodcut shows a ship flanked by two large floating trestles, forming a roof above the vessel. The ship is pulled in an upright position by a number of ropes attached to the superstructure.
The Saint-Nazaire's Chantiers de l'Atlantique owns one of the biggest in the world: . The Alfredo da Silva Dry Dock in Almada, Portugal, was closed in 2000. The largest roofed dry dock is at the German Meyer Werft Shipyard in Papenburg, Germany, it is 504 m long, 125 m wide and stands 75 m tall.
Harland and Wolff Heavy Industries in Belfast, Northern Ireland, is the site of a large dry dock . The massive cranes are named after the Biblical figures Samson and Goliath.
Dry Dock 12 at Newport News Shipbuilding at is the largest dry dock in the United States. The largest floating-dock in North America is named The Vigorous. It is operated by Vigor Industries in Portland, OR, in the Swan Island industrial area along the Willamette River.
The keel blocks as well as the bilge block are placed on the floor of the dock in accordance with the "docking plan" of the ship. Routine use of dry docks is for the "graving" i.e. the cleaning, removal of barnacles and rust, and re-painting of ships' hulls.
Some fine-tuning of the ship's position can be done by divers while there is still some water left to manoeuvre the vessel. It is extremely important that supporting blocks conform to the structural members so that the ship is not damaged when its weight is supported by the blocks. Some anti-submarine warfare warships have sonar domes protruding beneath the hull, requiring the hull to be supported several metres above the bottom of the dry dock, or depressions built into the floor of the dock, to accommodate the protrusions.
Once the remainder of the water is pumped out, the ship can be freely inspected or serviced. When work on the ship is finished, the gates are opened to allow water in, and the ship is carefully refloated.
Modern graving docks are box-shaped, to accommodate newer, boxier ships, whereas old dry docks are often shaped like the ships expected to dock there. This shaping was advantageous because such a dock was easier to build, it was easier to side-support the ships, and less water had to be pumped away.
Dry docks used for building naval vessels may occasionally be built with a roof, to prevent from taking pictures of the dry dock and any vessels that may be in it. During World War II, the German Kriegsmarine used fortified dry docks to protect its from Allied air raids (see submarine pen).
An advantage of covered dry docks is that work can take place in any weather; this is frequently used by modern shipyards for construction especially of complex, high-value vessels like cruise ships, where delays would incur a high cost.
A large floating dry dock involves multiple rectangular sections. These sections can be combined to handle ships of various lengths, and the sections themselves can come in different dimensions. Each section contains its own equipment for emptying the ballast tank and to provide the required services, and the addition of a bow section can facilitate the towing of the dry dock once assembled. For smaller boats, one-piece floating dry docks can be constructed or converted out of an existing obsolete barge, potentially coming with their own bow and steering mechanism.
Shipyards operate floating dry docks as one method for hauling or docking vessels. Floating drydocks are important in locations where porous ground prevents the use of conventional drydocks, such as at the Royal Naval Dockyard on the limestone archipelago of Bermuda. Another advantage of floating dry docks is that they can be moved to wherever they are needed and can also be sold second-hand. During World War II, the U.S. Navy used such auxiliary floating drydocks extensively to provide maintenance in remote locations. Two examples of these were the 1,000-foot AFDB-1 and the 850-foot AFDB-3. The latter, an Advance Base Sectional Dock which saw action in Guam, was mothballed near Norfolk, Virginia, and was eventually towed to Portland, Maine, to become part of Bath Iron Works' repair facilities. Photos of USS Samuel B. Roberts on blocks in AFDB-3 in 1988 "Sea Going Navy Yard Follows The Fleet", November 1945, Popular Science
A downside of floating dry docks is that unscheduled sinkings and off-design dives may take place, as with the Russian dock PD-50 in 2018.
The "Hughes Mining Barge", or HMB-1, is a covered, floating drydock that is also submersible to support the secret transfer of a mechanical lifting device underneath the Glomar Explorer ship, as well as the development of the Sea Shadow stealth ship.
The Great Balance Dock, built in New York City in 1854, was the largest floating drydock in the world when it was launched. It was long and could lift 8,000 tons, accommodating the largest ships of its day.
A dry dock may also be used for the prefabrication of the elements of an immersed tube tunnel, before they are floated into position, as was done with Boston's Silver Line.
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