Abstract: An apparatus and method for trenching beneath an elongated member lying on the bottom of a body of water are disclosed. The apparatus has a movable frame member, at least one cutting assembly, an assembly support means connected to the frame member for supporting each cutting assembly and for moving each cutting assembly at least in a laterally directed plane, and a spoil removal system. Each cutting assembly comprises at least two actuatable cutting tools which are driven for cutting movement relative to cutting tool axes. The cutting tool axes, for each cutting assembly, define an assembly cutting plane and means are provided for rotating the assembly cutting plane relative to the laterally directed plane, thereby, varying the cutting swath of the associated cutting assembly. In one aspect the method of the invention is directed to trenching from both sides of and beneath the elongated member to be buried.

Abstract: A method and apparatus for entrenching an elongated pipeline and the like uses a trenching apparatus having a trench cutting assembly which is detachably connected to a sled base. A floating vessel has means to control positioning of the trenching apparatus, including means to raise and lower, and to connect and disconnect, the trench cutting assembly and the sled base. Several methods and apparatus are disclosed for raising and lowering the trench cutting assembly while leaving the sled base positioned on the bottom of the body of water, straddling the elongated pipeline. In each embodiment, the cutting means may be lifted on board the vessel for maintenance and/or repair, leaving the sled base in position relative to the pipeline. Means are provided for abandoning the sled base at the entrenching site and returning later to lower the trench cutting assembly into its operational relationship with the sled base.