US Patent 7312416 Apparatus and methods for underwater welding

A lower housing having a lower chamber and a welding opening is fixed about an underwater weld site. The lower housing includes an upper opening, the lower housing being filled with water upon installation. A transport housing containing a welding unit in a dry state is lowered such that a bottom opening, closed by a closure element, registers with an upper opening of the lower chamber. Upon clamping the housings together, the lower chamber is at least partially evacuated. The closure element is then moved to an open position and the welding unit is lowered into the evacuated lower chamber to weld a patch to the vessel wall to overlay the damaged area.