108 



Another factor causing loss of station-keeping ability was ascribed to the 

 thruster's power sharing. One operator stated that when vertical thrust was 

 applied, forward thrust was automatically reduced. The result is a constant 

 jockeying back and forth to maintain station in the presence of even moderate 

 currents. 



The situation is helped somewhat on vehicles fitted with variable ballast 

 systems, providing the system can be cycled rapidly. In one instance the 

 operator abandoned this approach in favor of dynamic- rather than static - 

 vertical control owing to the. slow reacting time of the variable ballast 

 system. 



Several vehicles couple the data frqm a downward- looking echo sounder with 

 servos to control the vehicle's vertical thrusters to maintain a constant 

 distance-above-the-bottom. This technique performes satisfactorily over level 

 sea bottoms, but where the bottom is steeply sloping (45 degrees or more) 

 the system does not perform adequately since the returning echo is reflected 

 away from the vehicle's transducer. 



In one instance the operator decided to rely upon a more positive means of 

 station-keeping than thrusters. A technique for holding the vehicle to a 

 structure by limpet-like devices was developed for holding station while the 

 vehicle cleaned prior to conducting non-destructive testing. 



4.13 MANIPULATION 



In view of the limited call for manipulative tasks by industrially-oriented 

 vehicles, few operators expressed dissatisfaction with ROV manipulative 

 capabilities. One operating firm was of the opinion that tooling for the 

 manipulators required development in order to begin employing ROVs to their 

 full potential as manipulative vehicles. 



In another instance, the lack of a 3-dimensional perspective on current TV 

 monitors was identified as the causative factor for the limited success and/or 

 application of ROV manipulative devices. 



Lack of sophistication (i.e., degrees-of- freedom) in ROV manipulators was not 

 seen as an inhibiting factor since the excellent maneuverability of most 

 vehicles could serve to place the manipulator in the proper orientation. 

 In essence, ROV manipulation is considered more as an adjunct to the vehicle 

 rather than a major capability. 



4.14 PAY LOAD 



Vehicle payload (herein defined as the capability of the vehicle to accommodate 

 instrumentation in addition to those components routinely carried on a dive) 

 was considered inadequate in only one instance. In this case the operator 

 considered that at least 45kg (100 lbs) of additional payload was required 

 to meet all the tasks requested. 



In view of the fact that over 90 percent of all work conducted is obser- 

 vation and documentation, video or photographic, the need for additional 



