101 



it was in the process of inspecting an oil transmission line, its power supply 

 was interrupted and it drifted between the line it was inspecting and another 

 line immediately adjacent. When power returned to the vehicle the tide had 

 turned and the two lines were pushed together and prevented retraction of the 

 ROV. Not wishing to chance withdrawal of the vehicle through the two trans- 

 mission lines, the operator called in the services of a manned submersible. 

 The manned submersible inspected the situation and found it could not lift 

 the ROV. A tanker was coming in to the SALM and this forced the manned vehicle 

 to leave. Before leaving it cut the ROVs umbilical. Two months later the 

 vehicle was retrieved. The incident demonstrates that several factors caused 

 final abandonment. It also substantiates that ROV operators are as subject 

 to Murphy's Law as is the rest of the marine community. 



As a result of the potential for entanglement, ROV operators have adopted 

 several operating procedures to minimize the problem. One such (employed by 

 vehicles with subsea launchers - such as the RCV-225) is to enter structures 

 on the horizontal plane. If work above or below this plane is necessary, the 

 vehicle retraces its course out of the structure and then its launcher is 

 positioned higher or lower so that the vehicle can continue operating in the 

 horizontal plane only. Another procedure is to work on a structure only at 

 slack tide or to work on the down-current or leeward side of the structure so 

 that the umbilical will be forced away from the structure. The design of the 

 vehicle system can be of considerable assistance. Some vehicle systems employ 

 underwater launchers or clumps which hold the greater portion of the cable in 

 the vertical plane and allow the vehicle to operate from the launcher on a 

 short (150m or so) umbilical. This procedure is helpful toward decreasing the 

 possibility of entanglement with the support ship's screws, but entanglement 

 of the shorter umbilical still occurs. Streamlining or fairing the vehicle to 

 avoid entanglement is a somewhat uncertain (in terms of effectiveness) solution, 

 since fully faired vehicles have been entangled and the niomber of times the 

 vehicle avoided entanglement owing to its fairings is undeterminable. 



At this point in time there is no infallible method of avoiding cable entanglement, 

 and as long as the vehicle must rely on the umbilical cable for power, control 

 and data transmission, the ROV will be "hoisted on its own petard." Because the 

 very features which the ROV cable provides - long duration, unlimited power, 

 real-time data transmission - are purchased at the ever-attendant risk of cable 

 entanglement. 



4.2 ELECTRICAL CONNECTORS 



Almost half of the operators contacted expressed dissatisfaction with the 

 performance of ROV electrical connectors (i.e., where the umbilical cable 

 connects with the vehicle) . The scope of this study precludes conducting a 

 failure mode analysis of connector malfunctions. Consequently, only the highlights 

 and occurrence of such malfunctions were solicited. 



There is no particular failure common from vehicle-to-vehicle. Indeed, some 

 operators expressed no connector problems with a particular vehicle of a series 

 (e.g., the RCV-225 or the TROV/TREC or the SCORPIO series) while other operators 

 awning vehicles of the same series were quite dissatisfied. The cause or causes 

 of the problems are difficult to assess. Some operators categorically place 



