Cofferdam

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A cofferdam on the Ohio River near Olmsted, Illinois, built for the purpose of constructing the Olmsted Lock and Dam Cofferdam Olmsted Locks Ohio River.jpg
A cofferdam on the Ohio River near Olmsted, Illinois, built for the purpose of constructing the Olmsted Lock and Dam
A cofferdam during the construction of locks at the Montgomery Point Lock and Dam Dam Coffer.jpg
A cofferdam during the construction of locks at the Montgomery Point Lock and Dam

A cofferdam is an enclosure built within a body of water to allow the enclosed area to be pumped out or drained. [1] This pumping creates a dry working environment so that the work can be carried out safely. Cofferdams are commonly used for construction or repair of permanent dams, oil platforms, bridge piers, etc., built within water. They also form an integral part of naval architecture.

Contents

These cofferdams are usually welded steel structures, with components consisting of sheet piles, wales, and cross braces. Such structures are usually dismantled after the construction work is completed. [2]

The origin of the word comes from coffer (originally from Latin cophinus meaning 'basket') [3] and dam from Proto-Germanic *dammaz meaning 'barrier across a stream of water to obstruct its flow and raise its level'). [4]

Uses

For dam construction, two cofferdams are usually built, one upstream and one downstream of the proposed dam, after an alternative diversion tunnel or channel has been provided for the river flow to bypass the foundation area of the dam. These cofferdams are typically a conventional embankment dam of both earth- and rock-fill, but concrete or some sheet piling also may be used. Usually, upon completion of the dam and associated structures, the downstream coffer is removed and the upstream coffer is flooded as the diversion is closed and the reservoir begins to fill. Depending on the geography of a dam site, in some applications, a U-shaped cofferdam is used in the construction of one half of a dam. When complete, the cofferdam is removed and a similar one is created on the opposite side of the river for the construction of the dam's other half.

Cofferdams are used in ship husbandry to allow dry access to underwater equipment and to close underwater openings while work is done on the fittings inside the ship. This is more common in naval vessels where a cofferdam may fit several vessels of a class. [5]

The cofferdam is also used on occasion in the shipbuilding and ship repair industry, when it is not practical to put a ship in drydock for repair work or modernization. An example of such an application is the lengthening of ships. In some cases a ship is actually cut in two while still in the water, and a new section of ship is floated in to lengthen the ship. The cutting of the hull is done inside a cofferdam attached directly to the hull of the ship; the cofferdam is then detached before the hull sections are floated apart. The cofferdam is later replaced while the hull sections are welded together again. As expensive as this may be to accomplish, the use of a drydock might be even more expensive.

Cofferdams are also used in some marine salvage operations. [6] :Ch.10 Cofferdams have been used to recover aircraft from water as well, as in the case of Avro Lancaster ED603, which was recovered from the IJsselmeer in 2023 using a cofferdam, allowing for close examination of the wreckage, as well as to locate and repatriate the remains of its crew. [7]

Examples

A 100-ton open caisson that was lowered more than a mile to the sea floor in attempts to stop the flow of oil in the Deepwater Horizon oil spill has been called a cofferdam.[ citation needed ]

A cofferdam over 1 mile long was built to permit the construction of the Livingstone Channel in the Detroit River. [8] See main article at Stony Island.

The museum battleships USS Alabama (BB-60) and USS North Carolina (BB-55) have had cofferdams since 2003 and 2018, respectively. This saves much money compared to towing and dry docking them after the tow and this also provides additional security so there is a low chance of the ships sinking and becoming impossible to repair. [9] [10]

Types

Several types of structure performing this function can be distinguished, depending on how they are constructed and how they are used. [5]

Civil and coastal engineering

In civil and costal engineering applications cofferdams are usually made from interlocking steel sheet piles which are driven deep into the bed of the water source in order to create a temporary dam behind which the engineering contractors can carry out their works. After the construction project is complete the sheet piles can then be removed and the area behind them rewetted.

Inside of a cofferdam on a vessel Cofferdam TT A356.JPG
Inside of a cofferdam on a vessel

A cofferdam is a space between two watertight bulkheads or decks within a ship. It is usually a void (empty) space intended to ensure that the contents of nearly adjacent tanks cannot leak directly from one to the other which would result in contamination of the contents of one or both of the compartments. [11] The cofferdam would be kept empty at all times and the ship may have sensors within it to warn if it has begun to fill with liquid. If two different cargoes that react dangerously with each other are carried on the same vessel, one or more cofferdams are usually required between the cargo spaces.[ citation needed ]

Marine salvage

When all or part of the main deck of a sunken ship is submerged, flooded spaces cannot be dewatered until all openings are sealed or the effective freeboard is extended above the high water level. One method of doing this is to build a temporary watertight extension of the entire hull of the ship, or the space to be dewatered, to the surface. This watertight extension is a cofferdam. Although they are temporary structures, cofferdams for this purpose have to be strongly built, adequately stiffened, and reinforced to withstand the hydrostatic and other loads that they will have to withstand. Large cofferdams are normally restricted to harbor operations. [6] :Ch.10

Complete cofferdams cover most or all of the sunken vessel and are equivalent to extensions of the ship's sides to above the water surface. [6] :Ch.10

Partial cofferdams are constructed around moderate-sized openings or areas such as a cargo hatch or small deckhouse. They can often be prefabricated and installed as a unit, or prefabricated panels can be joined during erection. When partial cofferdams are used, it may be necessary to compensate for hydrostatic pressure on the deck by shoring the decks. With both complete and partial cofferdams, there is usually a large free surface in the spaces being pumped. Sometimes this can be limited by dewatering one compartment at a time, or in groups, taking into account the beam strength loads on the ship induced by the load distribution. [6] :Ch.10

Small cofferdams are used for pumping or to allow salvors access to spaces that are covered by water at some stage of the tide. They are usually prefabricated and fitted around minor openings. [6] :Ch.10

Diving work on cofferdams often involves clearing obstructions, fitting, and fastening, including underwater welding, and where necessary, caulking, bracing and shoring the adjacent structure. [6] :Ch.10

Ship husbandry

There are two common types of dry chambers used in underwater ship husbandry. Open bottom cofferdams allow divers direct access to the enclosed hull area, system, or opening. The flange sides of the chamber secure and seal against the hull, acting as an airtight boundary. Open bottom cofferdams are typically used as diver work space for rigging or welding and ventilation for welding or epoxy cure, where there is no opening to the interior of the vessel, or the interior is pressurised in this area. The air space is at the pressure of the water surface at the bottom of the chamber. Open top cofferdams allow surface access to the work area below the waterline, and are at atmospheric pressure. Openings through the hull to the interior of the ship are possible. [5]

Portable cofferdams

Portable cofferdams can be inflatable or frame and fabric cofferdams that can be reused. Inflatable cofferdams are stretched across the site, then inflated with water from the prospected dry area. Frame and fabric cofferdams are erected in the water and covered with watertight fabric. Once the area is dry, water still remaining from the dry area can be siphoned over to the wet area.[ clarification needed ][ citation needed ]

See also

Related Research Articles

<span class="mw-page-title-main">Hull (watercraft)</span> Watertight buoyant body of a ship or boat

A hull is the watertight body of a ship, boat, submarine, or flying boat. The hull may open at the top, or it may be fully or partially covered with a deck. Atop the deck may be a deckhouse and other superstructures, such as a funnel, derrick, or mast. The line where the hull meets the water surface is called the waterline.

<span class="mw-page-title-main">Dry dock</span> Basin drained to allow work on a vessel

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. Dry docks are used for the construction, maintenance, and repair of ships, boats, and other watercraft.

<span class="mw-page-title-main">Diving helmet</span> Rigid head enclosure for underwater diving

A diving helmet is a rigid head enclosure with a breathing gas supply used in underwater diving. They are worn mainly by professional divers engaged in surface-supplied diving, though some models can be used with scuba equipment. The upper part of the helmet, known colloquially as the hat or bonnet, may be sealed directly to the diver using a neck dam, connected to a diving suit by a lower part, known as a breastplate, or corselet, depending on regional language preferences. or simply rest on the diver's shoulders, with an open bottom, for shallow water use.

<span class="mw-page-title-main">Commercial diving</span> Professional diving on industrial projects

Commercial diving may be considered an application of professional diving where the diver engages in underwater work for industrial, construction, engineering, maintenance or other commercial purposes which are similar to work done out of the water, and where the diving is usually secondary to the work.

Underwater divers may be employed in any branch of an armed force, including the navy, army, marines, air force and coast guard. Scope of operations includes: search and recovery, search and rescue, hydrographic survey, explosive ordnance disposal, demolition, underwater engineering, salvage, ships husbandry, reconnaissance, infiltration, sabotage, counterifiltration, underwater combat and security.

<span class="mw-page-title-main">Deck (ship)</span> Part of a ship or boat

A deck is a permanent covering over a compartment or a hull of a ship. On a boat or ship, the primary or upper deck is the horizontal structure that forms the "roof" of the hull, strengthening it and serving as the primary working surface. Vessels often have more than one level both within the hull and in the superstructure above the primary deck, similar to the floors of a multi-storey building, that are also referred to as decks, as are certain compartments and decks built over specific areas of the superstructure. Decks for some purposes have specific names.

<span class="mw-page-title-main">Dredging</span> Excavation of sediment, usually under water

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<span class="mw-page-title-main">Bulkhead (partition)</span> Vertical partition inside a ship

A bulkhead is an upright wall within the hull of a ship, within the fuselage of an airplane, or a car. Other kinds of partition elements within a ship are decks and deckheads.

<span class="mw-page-title-main">Caisson (engineering)</span> Rigid structure to provide workers with a dry working environment below water level

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<span class="mw-page-title-main">Ship floodability</span> Susceptibility of a ships construction to flooding

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<span class="mw-page-title-main">Marine salvage</span> Recovering a ship or cargo after a maritime casualty

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<span class="mw-page-title-main">Moon pool</span> Opening in the base of a hull, platform, or chamber giving access to the water below

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<span class="mw-page-title-main">Salvage diving</span> Diving work associated with the recovery of vehicles, cargo and structures

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<span class="mw-page-title-main">Shipwrecking</span> Event causing a ship to wreck

Shipwrecking is an event that causes a shipwreck, such as a ship striking something that causes the ship to sink; the stranding of a ship on rocks, land or shoal; poor maintenance, resulting in a lack of seaworthiness; or the destruction of a ship either intentionally or by violent weather.

<span class="mw-page-title-main">Compartment (ship)</span> Portion of the space within a ship

A compartment is a portion of the space within a ship defined vertically between decks and horizontally between bulkheads. It is analogous to a room within a building, and may provide watertight subdivision of the ship's hull important in retaining buoyancy if the hull is damaged. Subdivision of a ship's hull into watertight compartments is called compartmentation.

<span class="mw-page-title-main">Ships husbandry</span> Maintenance and upkeep of ships

Ships husbandry or ship husbandry is all aspects of maintenance, cleaning, and general upkeep of the hull, rigging, and equipment of a ship. It may also be used to refer to aspects of maintenance which are not specifically covered by the technical departments. The term is used in both naval and merchant shipping, but naval vessel husbandry may also be used for specific reference to naval vessels.

Underwater work is work done underwater, generally by divers during diving operations, but includes work done underwater by remotely operated vehicles and crewed submersibles.

Underwater construction is industrial construction in an underwater environment. It is a part of the marine construction industry. It can involve the use of a variety of building materials, mainly concrete and steel. There is often, but not necessarily, a significant component of commercial diving involved. Some underwater work can be done by divers, but they are limited by depth and site conditions, and it is hazardous work, with expensive risk reduction and mitigation, and a limited range of suitable equipment. Remotely operated underwater vehicles are an alternative for some classes of work, but are also limited and expensive. When reasonably practicable, the bulk of the work is done out of the water, with underwater work restricted to installation, modification and repair, and inspection.

<span class="mw-page-title-main">Underwater cutting and welding</span> Metalworking techniques used by underwater divers

Underwater cutting and welding are metalworking techniques used by underwater divers in underwater construction, marine salvage and clearance diving applications. Most underwater welding is direct current wet stick welding, and most underwater metal cutting is immersed oxygen-arc and shielded metal-arc cutting, though other technologies are available and sometimes used. These processes are mostly applied to steel structures as that is the most common arc-weldable material used in the underwater environment.

Marine construction is the process of building structures in or adjacent to large bodies of water, usually the sea. These structures can be built for a variety of purposes, including transportation, energy production, and recreation. Marine construction can involve the use of a variety of building materials, predominantly steel and concrete. Some examples of marine structures include ships, offshore platforms, moorings, pipelines, cables, wharves, bridges, tunnels, breakwaters and docks. Marine construction may require diving work, but professional diving is expensive and dangerous, and may involve relatively high risk, and the types of tools and equipment that can both function underwater and be safely used by divers are limited. Remotely operated underwater vehicles (ROVs) and other types of submersible equipment are a lower risk alternative, but they are also expensive and limited in applications, so when reasonably practicable, most underwater construction involves either removing the water from the building site by dewatering behind a cofferdam or inside a caisson, or prefabrication of structural units off-site with mainly assembly and installation done on-site.

References

  1. Chisholm, Hugh, ed. (1911). "Cofferdam"  . Encyclopædia Britannica . Vol. 6 (11th ed.). Cambridge University Press. p. 649.
  2. "Cofferdam, Cofferdam Design, Cofferdam Applications – Dam-it Dams" . Retrieved 2016-09-25.
  3. Harper, Douglas. "coffer". Online Etymology Dictionary. Douglas Harper. Retrieved 14 December 2022.
  4. Harper, Douglas. "dam". Online Etymology Dictionary. Douglas Harper. Retrieved 14 December 2022.
  5. 1 2 3 "16. Cofferdams". Underwater Ship Husbandry Manuals (PDF) (Revision 0, Change H ed.). 15 November 2011. S0600-AA-PRO-160.PD-icon.svg This article incorporates text from this source, which is in the public domain.
  6. 1 2 3 4 5 6 U.S. Navy Salvage Manual (PDF). Vol. 1: Strandings, Harbor Clearance and Afloat Salvage S0300-A6-MAN-010. United States. Navy Department. Supervisor of Salvage and Diving. 31 May 2013. Archived (PDF) from the original on 5 April 2023. Retrieved 28 March 2023.
  7. "Chance for closure as RAF Lancaster and crew finally recovered after 80 years". www.forces.net. 2023-11-09. Retrieved 2024-07-13.
  8. "Detroit Free Press from Detroit, Michigan on March 27, 1910 · Page 65". Newspapers.com. 27 March 1910. Retrieved 2021-10-27.
  9. https://www.ussalabama.com/explore/park-history/ . Retreieved 13 April 2024.
  10. https://www.starnewsonline.com/story/news/2018/04/24/walkway-to-offer-new-views-perspective-of-battleship/12395353007/ . Retrieved 13 April 2024.
  11. Palmer, Joseph (1975). Jane's Dictionary of Naval Terms. London: Macdonald and Janes. ISBN   0-356-08258-X.