102 



the blame on lack of quality control at the manufacturing level, others accept 

 the problem as being brought about by poor handling techniques or lack of know- 

 ledge on their part. A common complaint is poor (unreliable) potting techniques 

 at the termination. Two operators have gone so far as to devise their own 

 potting procedures and rebuilding the connectors. The problem can be severe 

 when splicing of the termination is required which can take, in one instance, 

 from 30 to 3 6 hours. 



A specific complaint was that the soft metal sealing surfaces were damaged 

 during handling and were not suitable for field conditions. Further, the 

 complexity of the connectors was too great for field conditions and required 

 more care than could be given during at-sea operations. To correct this problem, 

 one operator has begun an in-house training program specifically designed for 

 instruction in the maintenance, repair and handling of electrical connectors. 



In only one instance did the surface connectors provide problems. In this 

 instance the winch slip rings were identified. 



4.3 SEDIMENT DISTURBANCE 



When working on or near the bottom several vehicle operators have confronted, 

 the problem of obscured visibility from sediment clouds produced by the ROVs 

 propeller wash. All but a few, ROVs operate a few kilograms positively buoyant 

 when submerged. In order to descend the vertical thrusters are employed. In 

 this instance the prop wash is directed above the vehicle and does not disturb 

 the sediment. The most' common circumstance under which sediment disturbance 

 is a problem is when the vehicle reverses thrust when it is on or immediately 

 near the bottom. Sand and hard rock bottoms do not present this problem, silt 

 and clay (i.e., mud) bottoms are critical. The sediment cloud produced can 

 interrupt the operation for some period of time depending upon the strength of 

 the prevailing current and the settling rate of the sediment. To combat this 

 problem, operators try to work facing into the current such that the disturbed 

 sediment will be carried downstream. 



No one vehicle appears to be immune from encountering this problem occasionally. 

 In some instances two different operators will have two different experiences 

 working with the same vehicle under similar or near-similar circumstances. 

 Obviously, pilot experience and expertise is a major factor in determining 

 the degree of bottom disturbance. 



At times it is necessary to work when on-going related activities result in 

 extensive bottom disturbance (e.g., pipe trenching). Tasks such as trench 

 profiling have been carried out in zero visibility, since the entire sequence 

 of the operation depends upon acoustic transmission for navigation and data 

 collection, and does not require remote observation. 



4.4 CABLE RUPTURE 



A variety of factors can be identified which result in rupturing of the umbilical 

 cable. Many of these are produced when the cable is entangled or fouled as 

 described in section 4.1. The overriding factor is mechanical abrasion by 

 synthetic lines, the bottom or a structure. Since most cables are negatively 



