1 A temporary structure in the form of an enclosed dam which can be erected on the seabed or the bed of a river and pumped dry to enable men to work within it below water level without having to wear diving suits. They are used largely in harbour works and for the construction of the piers of bridges. See also caisson.
2 Heavy transverse bulkheads in large merchant vessels, particularly tankers, built as a safety measure between the holds or oil tanks. They consist of a double bulkhead with a narrow space between them, the space frequently being used for the carriage of oil fuel or water ballast.