Self-propelled underwater trenching apparatus and method

An underwater trenching apparatus for burying pipeline and the like having a pipeline surface obstruction comprising:

• a frame for positioning about the pipeline to be buried,
• said frame including frame members positioned on each side of said pipeline,
• drive rollers connected to at least a fore portion of one of said frame members and to an aft portion of one of said frame members for drive engagement with said pipeline,
• first disengaging means to selectively alternately disengage at least one of said drive rollers from driving engagement with said pipeline in one portion of said frame member,
• drive means continuing to drive a drive roller in another portion of said frame member with sufficient force to move said apparatus along said pipeline a sufficient distance whereby said disengaged roller overrides said obstruction on the surface of said pipeline,
• second disengaging means to selectively and alternately disengage said previously engaged drive roller from said pipeline while said drive means drives said previously disengaged drive roller with sufficient force to move said apparatus along said pipeline, over said obstruction, and
• cutting means secured to said apparatus for cutting a trench in a formation whereby said pipeline is buried.

In a method of underwater trenching of a bottom formation for burying a pipeline by jetting a trench with an apparatus having frame members supported on the pipeline and driven by fore and aft pipeline engaging drive rollers, the improvement comprising,

• contacting the pipeline with the drive rollers in driving engagement,
• selectively and disengaging a forwardly positioned drive roller from driving engagement with said pipeline,
• driving an aft positioned drive roller to enable said forward drive roller to move forwardly along said pipeline and override an obstruction on the pipeline surface,
• selectively disengaging said aft positioned drive roller from driving engagement with said pipeline,
• engaging said forward drive roller in drive engagement with said pipeline to move said aft drive roller above said pipeline and override said obstruction.