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buoyant, their first action is to drag. Floats can be and are attached to keep 

 the cable suspended. This procedure is satisfactory when the vehicle does not 

 work from a launcher where the floats would interfere with the reeling in 

 process when the vehicle docks. 



The most commonly identified rupturer of umbilical cables is polypropelene 

 line. Such line is commonly used, for example, as buoy mooring lines for marking 

 pipeline right-of-ways. When an ROV is deployed to inspect the route, trench 

 or pipe itself the umbilical inadvertently chafes against the polypropelene. 

 Since the umbilical cable's outer sheathing is less tough than the polypropelene 

 line it is frequently chafed through to rupture. The problem can be quite 

 severe, indeed, one operator of several vehicles reported as many as 100 cables 

 ruptured in this fashion over an 18 month period. In this particular instance 

 replacement of the umbilical - though not always required - costs $3,000 (U.S.). 



Polypropelene line is not the only cause of mechanical abrasion. Also mentioned 

 are the sea bottom, structures (metallic and concrete) , wire rope mooring 

 cable and anchor lines. 



In virtually all present day deployment of ROVs the vehicle is deployed from 

 the surface. Consequently, the vast majority of the cable is suspended in the 

 water column and relatively immune from abrasion. However, one operator 

 deploys his vehicle from a manned submersible when it is sitting on the bottom. 

 With this technique almost the entire length of the negatively buoyant cable 

 can be subjected to bottom abrasion. Attachment of floats is impractical owing 

 to their interference with the reeling-out/reeling-in procedures. 



4.5 ELECTRICAL INTERFERENCE 



Problems with electrical interferences between the varied control, power, data and 

 video transmissions in the umbilical cable were revealed by several operators. 

 Interestingly, all but one of these operators employed vehicles built by non- 

 industrial manufacturers (i.e., academic institutions, research foundations, 

 government laboratories) . Operators of industrially-built vehicles acknow- 

 ledged minor interference in the early models, but those problems were subsequently 

 corrected. 



The most repeated interference effect is on TV signal transmission. This 

 problem, when it does occur, is almost always caused by the propulsion units. 

 The video picture is then, at best, subject to periodic fluttering; at worst, 

 it is completely blocked out. This latter situation occurs with one operator 

 when the paid out cable length reaches about 1km (3,168 ft). In one instance 

 it is not the surge of propulsive power itself, but is caused by the inverters 

 used for speed control. The result in this case, is interference with not 

 only the video signal, but the sonar and data telemetry as well. The operator 

 has minimized the interference, but cannot fully suppress it. 



While electrical interference is not a common problem from operator-to-operator, 

 it is the type of problem that is a major crisis to the one undergoing the 

 experience. It is the feeling of several operators that the problem has not 

 really surfaced at this stage of ROV employment. Since the predominant utilization 

 of vehicles is for observation, the opportunities for interference are relatively 



