26 



are used on the TROV and CETUS vehicles to gain neutral buoyancy at operating 

 depth and also to provide additional payload to acconunodate instrumentation 

 or v/ork tools beyond those routinely carried. Other ROVs provide extra payload 

 simply by adding more syntactic foam to the basic vehicle. The PAP-104 

 vehicles deploy a guiderope which drags along the bottom and holds the vehicle 

 at near-constant height above the bottom. 



2.1.3 Po wer 



All manufacturers but two rely on surface-supplied AC power? the two exceptions 

 relv on lead-acid, self-contained batteries (Table 2.1). The source of the surface- 

 supplied power is either ship's power or a dedicated diesel generator. 

 Operators are almost equally divided in their preference of one power source 

 over the other. Those who prefer a dedicated generator do so because at 

 sometime in their operations it has been necessary for the support ship's 

 Master to use his propulsion when the ROV is in a critical position within or 

 around a structure. The sudden drop in power to the ROV caused it to temporarily 

 lose power and, because of its inherent positive buoyancy, drift up into the 

 structure and entangle. This problem is avoided by use of a dedicated generator. 



Electrical requirements vary, but 50/60HZ and 220/240 VAC are most common. 

 Cable design varies from vehicle-to-vehicle. There is nothing in common between 

 cables, some are buoyant others are non-buoyant and require attachment of 

 floats to keep them from entangling with the vehicle or dragging on the bottom. 

 Most vehicles can be lifted out of the water by their umbilicals, but many 

 operators attach a short length (30 to 50m) of line to the vehicle which is 

 used to lift it clear of the water. Electrical interference in the cables 

 is infrequent, and occurs mostly in non-industrially-built vehicles. 



2.1.4 Propulsion/Maneuverability 



All ROVs except one employ propellers for propulsion; the exception (SMARTIE) 

 uses water jets. Several of the large vehicles shroud the propellers with 

 Kort nozzels for greater thrust under high slip conditions. Data from 

 92 vehicles show that 81 percent (75 vehicles) use electric thrusters, the 

 remainder use hydraulic. 



Six degrees of motion are produced by ROVs; three are translational : thrust, 

 heave, and sidle or sway; three are rotational: yaw, pitch, and roll. The 

 following indicates the precentage of vehicles which obtain these motions 

 dynamically. 



Thrust 100% 



Heave 96% 



Sidle or Sway 31% 



Yaw 100% 



Pitch 7% 



Roll 33% 



Only four vehicles are designed to obtain all six motions. 



2.1.5 Operating Depth 



Maximum vehicle operating depths range from 100 to 6,095m (328 to 20,000 ft). 

 The distribution of vehicles vs. operating depth is shown in Figure2.4and 



