100 



Operator I - Cable wrapped in anchor line it was inspecting, support 



ship pulled away inadvertently and broke cable. 



Vehicle propeller fouled by monofilament fishing line. 



Cable tangled with marker buoy mooring line. 



Cable cut by polypropelene mooring line. 

 Operator J - Cable fouled in support ship's anchor chain. Anchor had to 



be retrieved to free cable. 



Vehicle tangled by abandoned lines on fixed structure. 

 Operator K - Vehicle tangled by abandoned fishing lines on structure. 



Cable fouled in support ship's propeller and severed. 



Cable fouled, resultant kinking caused short circuit. 

 Operator L - Cable wrapped around bottom-mounted navigation transponder. 



Cable fouled (twice) in support ship's propellers. 

 Operator M - Cable wrapped around support ship's anchor chain. 

 Operator N - Cable caught in support ship's propeller (three separate 



occasions) . 

 Operator O - Cable fouled on SALM (Single Anchor Leg Mooring) mooring 



line, vehicle abandoned for eight weeks, subsequently 



retrieved by manned submersible. 



The foregoing incidents are but a sampling of the many instances of cable and 

 vehicle entanglement. Others have occurred which have not been documented, 

 but reveal even more the vast potential for fouling every time a tethered 

 vehicle is deployed. For such reasons several operators not only carry spare 

 cables, but backup vehicles as well. While an exact count is difficult to 

 obtain, at least 12 ROVs have been lost; in virtually every instance it was 

 due to cable or vehicle fouling. Such incidents have prompted one operator 

 to refuse work which requires the vehicle to operate around or within fixed, 

 upright structures. 



The causes of entanglement are varied and no single factor appears to be over- 

 riding. Operator error undoubtedly plays a large role. While the operator may 

 be aware of the vehicle's position, he may not be aware of the umbilical 's 

 and it may have drifted into a compromising situation. Equally significant 

 are the entanglement situations derived from discarded debris and lines. 

 Several operators reported that fixed structures, particularly those which have 

 been installed for a period of several years or more, are literally festooned 

 with snagged monofilament fishing tackle from fishing activities of the crew. 

 In a similar vein, the bottoms of harbors and other areas of high marine activities 

 are likewise cluttered with a wide variety of debris. In such circumstances, 

 there is little the operator can do to avoid entanglement other than to dive 

 where visibility is adequate. Propeller guards help the situation somewhat, 

 but are not always a positive solution. In some instances the power supply can 

 be identified as the cause of entanglement, this is discussed in a later 

 section, but, several incidents have occurred where the vehicle's power was 

 temporarily interrupted and, by virtue of its positive buoyancy, it ascended 

 into a structure and fouled. An additional factor is the water current which 

 carries the umbilical into a structure while the vehicle itself remains outside. 



In many instances several of the above factors work together to produce the 

 entanglement and subsequent abandonment of the vehicle. An example of this is 

 the experience of Operator O, where the vehicle was abandoned for two months. 

 In this incident the vehicle was launched from an anchored support ship. As 



