A cofferdam is a watertight structure used for construction in submerged areas. It can be made of various materials and can be open or enclosed. It is used for worker safety and can also be portable for ship repairs.
A cofferdam is a type of watertight construction designed to facilitate construction projects in normally submerged areas, such as bridges and wharves. One is installed in the work area and water is pumped to expose the water body bed so workers can build structural supports, make repairs, or do other types of work in a dry environment. In some regions of the world, this construction is better known as a caisson. Working within a cavity can be dangerous if it is improperly installed or not safely pressurised, but advances in engineering have led to increased safety for workers using this unique work environment.
A variety of materials can be used to construct a cofferdam, which is truly a feat of engineering. While a temporary structure, it must reliably retain water from the work area and also withstand very high pressures to be safe, and the construction is often used as a blueprint for engineers learning their trade. The most basic type uses sheet metal, which is hammered into the bed of the body of water to create an airtight wall. Next, pumps are used to draw the water out of the casing so that it is dry. Some are constructed of wood or concrete, while others use a double wall mechanism, with filler made from aggregate materials between the two walls.
The walls of a cofferdam can extend to the surface of the water, leaving it open at the top, or it can be built as an enclosed structure. In very deep water, closed and pressurized ones are used for worker safety, while in shallower bodies of water, an open structure may be used. Workers enter an enclosed cavity through hatches and pipes and care is taken to ensure that the air supply is consistent and pressure is maintained at a normal level.
Shipwrights and repair yards also use a portable version, which can be attached to the side of a vessel to carry out repairs below the waterline. At sea, this can be a useful way to address potential problems quickly until the vessel is dry docked for a more long-term repair. Minor repairs can also be done with a laptop in a shipyard to avoid the expense of hauling the ship into dry dock to complete the job.
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