A drydock 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. Drydocks are used for the construction, maintenance, and repair of ships, boats, and other watercraft.
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1 Hi Hist stor ory y 1.1 Ptolemaic Egypt o 1.2 1. 2 Ch China ina o 1.3 Renaiss Renaissance ance Europe o 1.4 Modern times o 2 Ty Type pess 2.1 2. 1 Gra Gravi ving ng o 2.2 Floa Floating ting o 2.3 Alternative drydock systems o 3 Uses other than for ships 4 See also als o 5 Ref Referen erences ces
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6 Exte Externa rnall link linkss
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[edit edit]] History [edit edit]] Ptolemaic Egypt According to the ancient Greek author Athenaeus author Athenaeus of Naucratis, Naucratis, the drydock was invented in Ptolemaic Egypt, Egypt, some time after the death of Ptolemy of Ptolemy IV Philopator (reigned Philopator (reigned 221-204 BC): But after that (the reign of Ptolemy IV Philopator) a Phoenician devised a new method of launching it (a ship), having dug a trench under it, equal to the ship itself in length, which he dug close to the harbour. And in the trench he built props of solid stone five cubits deep, and across them he laid beams crosswise, running the whole width of the trench, at four cubits' distance from one another; and then making a channel from the sea he filled all the space which he had excavated with water, out of which he easily brought the ship by the aid of whatever men happened to be at hand; then closing the entrance which had been originally made, he drained the water off again by means of engines (organois); and when this had been done the vessel rested securely on the before-mentioned cross-beams. cross-beams .[1]
Since Athenaeus recorded the event 400 years later (around 200 AD), A D), there is sufficient reason to believe that drydocks had been known throughout classical antiquity.
[edit edit]] China
Drydocks appeared in China by 1070 A.D. In 1088, Song Dynasty scientist and statesman Essays: Shen Kuo (1031–1095) wrote in his Dream his Dream Pool Essays: At the beginning of the dynasty (c. +965) the two Che provinces (now Chekiang and southern Chiangsu)) presented (to the throne) two dragon ships each more than 200 ft. in length. The upper Chiangsu works included several decks with palatial cabins and saloons saloons,, containing thrones and couches all ready for imperial tours of inspection. After many years, their hulls decayed and needed repairs, but the work was impossible as long as they were afloat. So in the Hsi-Ning reign period (+1068 to +1077) a palace official Huang Huai-Hsin suggested a plan. A large basin was excavated at the north end of the Chin-ming Lake capable of containing the dragon ships, and in it heavy crosswise beams were laid down upon a foundation of pillars. Then (a breach was made) so that the basin quickly filled with water, after which the ships were towed in above the beams. The (breach now being closed) the water was pumped out by wheels so that the ships rested quite in the air. When the repairs were complete, the water was let in again, so that the ships were afloat once more (and could leave the dock). Finally the beams and pillars were taken away, and the whole basin covered over with a great roof so as to form a hangar hangar in in which the ships could be protected from the elements and avoid the damage caused by undue exposure. ( Wade-Giles spelling.)[2]
[edit edit]] Renaissance Europe
Floating Dock. Woodcut from Venice (1560). In Europe, the first drydock, and the oldest surviving drydock, was commissioned by Henry VII of England at HMNB Portsmouth in 1495 (see The Tudors and the Royal Navy). Navy ). This drydock currently holds the worlds oldest commissioned warship HMS Victory.. Victory Possibly the earliest description of a floating dock comes from a small Italian book machina .[3] In the booklet, printed in Venice in 1560, called Descrittione called Descrittione dell'artifitiosa machina. 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 hanging h anging down from the roof.
[edit edit]] Modern times
The Harland and Wolff cranes Wolff cranes in Belfast Belfast,, Northern Ireland. Ireland. Harland and Wolff Heavy Wolff Heavy Industries in Belfast Belfast,, is currently the largest in the world and is close to the slipway on which the ill-fated RMS Titanic was constructed. The massive cranes are named after the Biblical figures Samson and Goliath Goliath.. Goliath stands 96m tall, while Samson is taller at 106m. Northrop Grumman Newport News Shipbuilding's Dry Dock 12 is the largest drydock in the USA. The Saint-Nazaire Saint-Nazaire''s Chantiers de l'Atlantique owns one of the biggest in the world : 3937 feet x 196.850 feet. The largest graving dock of the Mediterranean as of 2009 is at the Hellenic Shipyards S.A. (HSY S.A., Athens, Greece)[1] Greece)[1].. The by far largest roofed dry dock is at the German Meyer Werft Shipyard in Papenburg Papenburg,, Germany Germany,, it is [4] 504m long, 125m wide and stands 75m tall.
[edit edit]] Types
The brig The brig Stockholm in one of the historical drydocks on the island Beckholmen in central Stockholm.. Stockholm
[edit edit]] Graving The classic form of drydock, properly known as graving dock, is a narrow basin, b asin, usually made of earthen berms and concrete, closed by gates or by a caisson 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. A distinction needs to be made between drydocks
that are intended for ship construction sites, and those that are designed for the maintenance and repair of ships - especially for the repair of battle damage. More routine use of drydocks is for the cleaning (removal of barnacles and rust) and re-painting of ship's hulls. Some fine-tuning of the ship's position can be done by 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 anti-submarine warfare warships have protruding sonar sonar domes, 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 re-enter the dry dock and the ship is carefully refloated. 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. Drydocks used for building Navy vessels may occasionally be b uilt with a roof. This is done to prevent spy satellites from taking pictures of the drydock and any ships or submarines that may be in it. During World War II covered drydocks 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 drydocks are usually used only when servicing or repairing a fleet ballistic missile submarine.. Another advantage of covered drydocks is that one can work independently of submarine the weather. This can save time in bad weather.
[edit edit]] Floating
The towboat, DOLPHIN I, in a floating drydock on the Mississippi river in Algiers, Louisiana.
Blohm + Voss, Port of Hamburg A floating drydock is a type of pontoon pontoon for dry docking ships, possessing floodable buoyancy chambers and a "U" shaped cross-section. The walls are used to give the drydock stability when the floor is below the water level. When valves are opened the chambers are filled 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 drydock rises and the deck is cleared of water, allowing work to proceed on the ship's hull. Shipyards operate floating drydocks, among other means of hauling or docking vessels. The advantage of floating drydocks is that they can be moved all over the world and also can be sold second-hand. During World War II, II, the U.S. Navy used such (floating) drydocks extensively to provide maintenance in remote locations. One of these, the 850foot AFDB-3 AFDB-3,, saw action in Guam Guam,, was mothballed near Norfolk Norfolk , Virginia Virginia,, and was eventually towed to Portland Portland,, Maine Maine,, to become part of Bath of Bath Iron Works' Works' repair facilities. [5]
The "Hughes "Hughes Mining Barge", 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, Explorer ship, as well as the development of the Sea Shadow stealth ship. ship.
[edit edit]] Alternative drydock systems Apart from graving docks and floating drydocks, ships can also be drydocked and launched by: • •
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Mobile boatlift (also called Travelift, for vessels up to 1000 metric tons)[2] tons)[2] Slipway,, patent slip — For repair of smaller boats and the newbuilding launch of Slipway larger vessels Marine railway — railway — For repair of larger ships up to about 3000 tons ship weight Shiplift — Shiplift — For repair as well as for newbuilding. From 800 to 25000 ton shipweight
[edit 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 Neeltje-Jans was used for the construction of the Oosterscheldekering Oosterscheldekering,, a large dam in the Netherlands the Netherlands that consists of 65 concrete pillars weighing 18,000 tonnes each. The pillars were constructed in a drydock and towed to their final place on the seabed. They may also be used for the prefabrication of the elements of an immersed tube tunnel, before they are floated into position.
[edit edit]] See also • • •
Space dock Semi-submersible St. Nazaire Raid — Raid — an attack on a drydock during WW2 WW2..
What is Drydock and why it is done? We learnt in another article about types of ship repairs and know that a ship needs to be kept in ship-shape by following various methods described over there. Drydocking was mentioned as one of the methods and can be compared to taking your car to the garage for maintenance. All marine vessels ranging from say the smallest F1 Power Boat to the largest cruise liner of liner of the world need repairs. The garage mechanic simply uses hydraulic aid to lift your car off the ground, but the same cannot be said about big ships such as bulkers bulkers,, tankers tankers,, reefers or any type of ship for that matter and it is there that the concept of a drydock comes into the picture. Dry dock is a large dock made out from the shore, from which water can be pumped out in order to repair parts of the ship which are below the waterline waterline.. According to a SOLAS requirement, every sea going ship should be dry docked at least twice every 5 years. Dry docks should also be carried out if demanded by the Classification Society. This is usually asked to be done in case the ship has met with a collision, has been grounded in past or has a lousy maintenance practice. Inspection during dry docking is also carried out if the ship is to be sold. Also, the time gap between two drydocks shouldn't be more than 3 years. Excemptions are provided only if the ship is well maintained and that too just by replacing one drydock with an in water survey.
Dry Dock Methods The type of Dry docking method selected depends on the type of the ship and the severity of maintainence and repair required. The four main types of Dry docking Methods are as follows: • • • •
Floating Dock Excavated Dock Patent Slip Ship lift
Floating Dock A Floating Dock is a kind of a pontoon with sponsons on both the sides. The pontoon is divided into number of tanks. When the ship has to be docked, the tanks are filled with water due to which the dock submerges into the water. The
ship is then navigated into the dock and the tanks are emptied so that the dock
rises above the water. The pumping of water is done with the help of ballast pumps which are located in sponsons. The sponsons are also equiped with cranes and bollards. Both the sponsons are connected with a bridge. Apart from the ballast pumps, the water is also filled manually with the help of manual valves. To prevent any movement of the ship, keel blocks are provided. These keel blocks are placed on the tanktops. For increased stability side blocks are also provided.The side blocks are provided in such a way that the forces they exert don't damage the hull. Special reinforcement material is provided to prevent this.
1)Keel Blocks 2)Side Blocks 3)Side Sponson 4)Rails for crains
Excavated Dock This method of docking is almost similar to that of Floating dock. The Only difference is that it has a closing door at the opening. Also, the dock is sloped slightly towards the opening and the ballast pumps are located near the door itself. Excavated dock can be a floating structure or a dock at the harbour.
Patent Slip This system is generally used for small ships of length 140 meters or less. It works some thing like the "jack up" system. The system consists of cradles that moves with the help of rails. The cradles roll into the water till they reach exactly beneath the ship. Once there, they are pulled in a perpendicular direction which brings the ship above the water surface.
Ship lift This system is somewhat similar to the Patent Ship method. It also consists of cradles which are used to slid a platform into the water, below the ship. Once the platform reaches below the ship, the ship is properly navigated on the platform.After that, Winches are used to lift the ship and to place it in the desired position. This system can lift ships only of length up to 125 meters. Approximately 14 cradles are used to move the platform.
Dry Docks Dry docks have always been the “Cinderella” of harbour engineering. No one seems to take much notice of them. I have made them my particular speciality and tried to develop a coherent approach to the subject. In particular I have set out to develop a theory of dry docking. Slipways are a particularly neglected style of dry docking – a direct result of the lack of a coherent design theory. One can usually tell, just by looking at a dry docking facility, which parts have been designed by a civil engineer, which by a naval architect. Neither, unless they specialise in dry docking — which is rare — have any feel for the subject. The various types of dry docks are • • • • • •
GRAVING DOCKS FLOATING DOCKS SHIPLIFTS SLIPWAYS TRANSFER SYSTEMS SMALL CRAFT LAUNCHING RAMPS
The slipway, a cradle on wheels on rails running down into the sea, was patented in 1819 in Scotland by Thomas Morton. The original form was pretty primitive and here at the Cape, in South Africa, developed a particular form of their own. My involvement in this field started with these simple “Cape” type slipways. This is my first slipway, a basic “Cape” system in the fishing harbour of Gansbaai to which I added a docking frame and hydraulic bilge support arms operated by handpump from the catwalk on the docking frame. It has a separate side slip cradle riding “piggy–back” on the main cradle.
My next slipway was built for the South African Navy in Simonstown for their small craft and yachts. This one doesn't have hydraulic bilge arms — that would have been a bit too much for the Navy to swallow in one gulp. The inovation in this one was the construction of the ways. They are set to a verical circular curve — the first in Africa. The ways structure was constructed in steel in the Naval Dry Dock, floated out and set onto precast concrete pedestals and clamped to these by removable clamps. These in turn had been set in place to very accurate levels by framed jigs that located each pair accurately in alignment from thee pr th prev evio ious us pa pair ir an and d en ensu sure red d th that at th thee pr pref efab abri rica cate ted d wa ways ys fi fitt tted ed th thee pe ped des esta tals ls.. The slipway in the fishing harbour of Lamberts Bay embodied all the technical innovations I had developed over the previous 15 years. It was designed in accordance with Lloyds Register Rules for Lifting Appliances in a Marine Environment and checked and certified by them — the first in Africa to get this certification. It was for the design and construction of this facility that I was awar aw arde ded d th thee So Sout uth h Af Afri rica can n In Inst stit itut utio ion n of Ci Civi vill En Engi gine neers ers Ba Basi sill Re Read ad Go Gold ld Me Meda dall fo for r Construction.
I built the 2000 ton lift Syncrolift© shiplift at Walvis Bay in 1972 and supervised the management of it and the technical services until 1991. It was during this period that I developed the rope maintenance procedures reported in my paper “Cor “C orro rosi sion on in Me Mech chan anic ical al Dr Dry y Do Dock ckin ing g Sy Syst stem ems” s” (s (see ee TEC TECHN HNICA ICAL L PAP PAPERS ERS). ). On two occassions I have had to salvage shiplifts, this one and the South African Navy shiplift in Durban. I have also been involved in prefeasibility and feasibility studies, on behalf of the Namibian Port Authorities, for increases dry docking facilities in Walvis Bay leading to the provision of an 8000 ton lift floating dock in the port.
Recently, Recent ly, the Sou South th Afr Africa ican n Nat Nation ional al Por Portt Authority asked me to take over the running of their dry docking facilities during a management crisis. The picture shows the 370m Sturrock dock during this period with blocks set for two ships. Thee af Th aftt se sett ha hass hi high gh bi bilg lgee bl bloc ocks ks cr crib ibbe bed d fo forr st stab abil ilit ity y in wa way y of th thee st ster ern n cu cut– t–up up..
In the course my career I have had something to do with all types of dry dock spread across the whole spectrum activities. As a result I am able of offer assistance in all aspects of dry docking.
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MARKET SURVEYS DRY DOCK FEASIBILITY STUDIES DRY DOCK DESIGN PROJECT MANAGEMENT OF CONSTRUCTION TO COMPLETION DRY DOCK SURVEYS
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DRY DOCK RATING SYSTEM UPGRADIN UPGRADING G DOCKING STAFF TRAINING ADVICE ON DIFFICULT DOCKING FORENSIC ANALYSIS OF AND REPORTING ON DRY DOCK ACCIDENTS SALVAGE OF DRY DOCK SYSTEMS AFTER AN ACCIDENT DRY DOCK MANAGEMENT DRY DOCK MAINTENANCE
