Dry dock

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Image:Zadm drydock.jpg A 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.

1 History
2 Types
3 Uses other than for ships
4 Footnotes
5 See also

[edit] History

[edit] Antiquity

According to the ancient Greek author Athenaeus of Naucratis, the dry dock was invented in Greek Egypt, some time after the death of Ptolemy IV Philopator (reigned 221-204 BC):

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Since Athenaeus recorded the event 400 years later (around 200 AD), there is sufficient reason to believe that dry docks had been known throughout classical antiquity.

[edit] China

In China dry docks appeared no later than 1070.^{[citation needed]}

[edit] Renaissance Europe

In Europe, the first dry dock, and the oldest surviving dry dock, was commissioned by Henry VII of England at HMNB Portsmouth in 1495 (see The Tudors and the Royal Navy).

Possibly the earliest description of a floating dock comes a small Italian book printed in Venice in 1560, called Descrittione dell'artifitiosa machina.<ref>George Sarton, Floating Docks in the Sixteenth Century, Isis, Vol. 36, No. 3/4. (Oct., 1946), pp. 153-154 (153)</ref> In the booklet, an unknown author asked 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 hanging down from the roof.

[edit] Modern times

The largest dry dock in the world is in Belfast, Northern Ireland measuring 556m (1824 ft) by 93m (305 ft), with a capacity of 1.2 million tonnes.

[edit] Types

[edit] Graving dry dock

A graving dry dock is a narrow basin, usually made of earthen berms and concrete, closed by gates or by a caisson, into which a vessel may be floated and the water pumped out, leaving the vessel supported on blocks. 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.

Some fine-tuning of the ship's position is done by scuba divers while there is still some water left to manoeuvre it about. 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 ASW warships have protruding sonar domes, requiring that the hull of the ship be supported several meters from the bottom of the drydock.

Once the remainder of the water is pumped out, the ship can be freely inspected or serviced. When work on the ship is finished, water is allowed to reenter the dry dock and the ship is carefully refloated.

A graving dock is a multi-purpose dock. It can be used for new building, for repair, and for maintenance. The word "graving" was more often used to denote the cleaning of a ship's bottom.

Modern graving docks are box-shaped, to accommodate the newer, boxier ship designs, whereas old drydocks are often shaped like the ships that are planned to be docked 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.

U.S. Navy ballistic missile submarine USS Michigan inside a flooded drydock

Dry docks that are used for building Navy vessels may occasionally be built with a roof. This is done to prevent spy satellites from taking pictures of the dry dock and any ships or submarines that may be in it. During World War II covered dry docks were frequently used by submarine fleets to protect them from enemy air raids, however their effectiveness in that role diminished after the Second World War. Today covered dry docks are usually used only when servicing or repairing a fleet ballistic missile submarine. Another advantage of covered dry docks is that one can work independent of the weather. This can save considerable time.

[edit] Floating dry dock

Image:USS Iowa Floating Drydock.jpg

A floating dry dock is a salvage platform which has floodable buoyancy chambers in a "U" shaped cross-section that can support a ship. When valves are opened to fill the chambers with water, the dry dock floats lower in the water, allowing a ship to be moved into position inside. When the water is pumped out of the chambers, the dry dock rises and the deck is cleared of water, allowing work to proceed on the ship's hull.

Floating dry docks are often operated by shipyards, but can also be moved around the world as needed — some split into sections for easier towing. During World War II, the U.S. Navy used such dry docks extensively to provide maintenance in remote locations. One of these, the 850-foot AFDB-3, 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

[edit] Other ways of drydocking ships

Apart from graving docks and floating drydocks, ships can also be drydocked and launched by:

Mobile boatlift (also called Travelift, up to about 250 tons weight)
Slipway, patent slip — For repair of smaller boats and the newbuilding launch of larger vessels
Marine railway — For repair of larger ships up to about 3000 tons ship weight
Shiplift — For repair as well as for newbuilding. From 800 to 25000 ton shipweight

[edit] Uses other than for ships

Some drydocks are used during the construction of bridges, dams, and other large objects. For example, the drydock on the artificial island of Neeltje-Jans was used for the construction of the Oosterscheldekering, a large dam in the Netherlands that consists of 62 concrete pillars weighing 18,000 tonnes each. The pillars were constructed in a drydock and towed to their final place on the seabed.

Image:Dry dock in Singpore.jpg