Bottom fishing equipment routinely damage or break important Navy oceanographic cables resulting in substantial repair costs and unacceptable interruptions. The Civil Engineering laboratory (CEL), sponsored by the Naval Facilities Engineering Command (NAVFACENGCOM has developed and validated an engineering concept for a Deep Ocean Cable Burial (DOCB) system. The DOCB system provides an effective and reliable means of burying cables 3 ft deep in ocean sediments, at speeds greater than 1 knot, to water depths of 6,000 ft.
The DOCB system concept is a remotely controlled machine which under runs and buries existing (previously laid) cables. It is powered and controlled from a surface ship via an electro-mechanical umbilical cable. The machine is self-propelled by ducted thrusters and supported on water lubricated skids. The excavation system comprises an orbital vibrating plowshare and a vertical water jet. This paper presents the results of full scale field tests at CEL on the excavation and skid systems.
Full scale field testing of individual components as shown that a 70% reduction in drawbar force was achieved by applying an elliptical orbital vibration. It was also shown that the vibration feature would split or push aside buried rocks which would have stalled a conventional stationary plow.
The water jet tests demonstrated that a 2-1/2" nozzle cuts 36" deep in 1-2 psi of clay at a nozzle pressure of 75 psi and flow of 1200 gpm. Also tests with the skid system showed that forcing a layer of water between the skid and soil reduced the skid/soil drag by 50% in both sand and clay.
Oceanographic cables laid on the seafloor have proved to be vulnerable to damage and ensuing failure from the otter boards of bottom fishing trawlers. The Civil Engineering laboratory, sponsored by the Naval Facilities Engineering Command initiated a development effort to synthesize a concept for a system to effectively bury the cables 3 feet deep in the seafloor to ocean depths of 6000 feet. The Deep Ocean Cable Burial (DOCB) concept (Figure 1) comprises ducted thrusters for propulsion, water lubricated skids, and two excavation means - a vertically impinging water jet followed by an orbitally vibrating plowshare, as well as a variety of other supportive subsystems.
Of all the subsystems which are required for the DOCB system, only the orbital vibratory plow, the vertical water jet, and the water lubricated skids had not been proven in situations similar to those that would be encountered during a cable burial operation.
Vibratory plowing as a means to create a trench for burying cables was selected as one of the primary excavation subsystem candidates during the DOCB concept development.
