Under ice pipelaying

Abstract

A method of laying an underwater pipe line under an ice sheet. The pipe is fabricated on shore at a make-up point and a plurality of support stations are spaced apart along the pipe path. Holes are bored in the ice at the support stations and low friction pipe support cradles are lowered underwater at the stations and anchored to the ice sheet. A trench is then cut in the ice and the pipe string is introduced into the water and towed across beneath the ice surface through the support cradles by means of pulling winches at a winching station or stations. As the leading end of the pipe being towed under the ice passes each support station the pipe support cradles are tightened so as to support the pipe string from the ice sheet and immediately beneath it. After the pipe has been towed to the opposite shore, the pipe is lowered to the water bottom by attaching a train of lowering winches to the pipe through the trench. Each of the lowering winches take up the support of the pipe and lowers it in turn to the water bottom as corresponding support cradles are released, one after the other.

Dependencies are inferred from the claim text.