Disclosed is an underwater laying device for offshore oil and gas pipelines. By using a steel cuboid as the main body, a first mud-plowing rake, a first mud-plowing hoe, a second mud-plowing rake, a second mud-plowing hoe, and a mud delivery plate are disposed on the lower surface of the cuboid main body. Further, by cooperation of a mud collection hood and an elongated pipeline-delivery cylinder, and according to structural characteristics of traditional farming tools, submarine trenching, pipeline laying, and pipeline burying can be successively performed and all implemented by the device of the present invention. Further disclosed is a pipeline laying method of the device of the present invention. The device of the present invention has a simple structure, and overcomes the structural complexity of the conventional underwater robot on the premise of achieving the function requirements, thus greatly reducing the manufacturing cost and being mass-producible.

A depressor (16) for inserting a cable (4) into a trench (6) is disclosed. The depressor (16) comprises a plurality of cable shoes (22) adapted to be mounted to a support (18) and to engage the cable (4). Locating pins substantially prevent movement of the cable shoes (22) relative to the support (18) in a first direction as a result of movement of the cable shoes (22) relative to the cable (4) in an axial direction of the cable (4). A load cell provides an output dependent on a force applied to the cable shoes (22) in a second direction transverse, or perpendicular, to the first direction.

The disclosure belongs to the technical field of underwater operations, in particular relates to an operation system and an operation method for underwater jet trenching and cable laying. The underwater walking device is provided at a lower end of the main body; the two jetting arms is located at a front end of the main body; the jetting suction device is arranged at a rear end of the main body and includes a suction pipeline and a second jetting pipe, the suction pipeline is configured to suck sediment in the trench through the suction port before a cable settles to the bottom of the trench and to discharge the sediment to outside of the trench through the discharge port; the second jetting pipe is configured to spray a horizontal jet to scour an inner side wall and the bottom of the trench along the length direction of the trench.