Суды кесуге арналған тоспалар

Barrier allowing liquid to be pumped out of an enclosed area

A cofferdam is an enclosure built within a body of water to allow the enclosed area to be pumped out or drained. 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. 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. The origin of the word comes from coffer (originally from Latin cophinus meaning 'basket') and dam from Proto Germanic dammaz meaning 'barrier across a stream of water to obstruct its flow and raise its level').

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. 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.

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