Coffer-dam

Usually a wooden construction in form of a large box, so designed as to fit closely round a ve el’s bow or stern, and when pumped out affording acce to parts below the water-level, requiring repair. Also a case, open ended below, constructed usually of plate iron, either rectangular or cylindrical in form, and made watertight; then sunk to the bottom of a river and the contents pumped out dry, leaving the bed of the stream so enclosed, acce ible to workmen employed inside the „ Dam ”.