39 



Prior to the present full-scale application of ROVs in the offshore industrial 

 community many manufacturers advertised that their vehicle could be deployed 

 from virtually any "Ship of Opportunity". The past two years of open ocean 

 operations, particularly in the North Sea, have shown this term to be largely 

 optimistic. Experience has demonstrated that an ROV is one component of a 

 system which consists of the support platform, the launch/retrieval device 

 and the vehicle itself. As operations with manned vehicles demonstrated, the 

 system is only as strong as any of these components; the ROV system is bound 

 by similar constraints. The capabilities of the support ship are as important 

 as are the capabilities of the ROV. Equally important are the abilities of 

 the support ship's crew. In spite of the tremendous technological advances 

 achieved in the marine community, sound seamanship is as important now as it 

 was in years past. Indeed, the requirements for maintaining a prescribed 

 "footprint" over a submerged ROV without fouling the umbilical places demands 

 on the support ship's Master equal to any in the offshore community. 



.Operations are conducted in two modes: anchored (or moored) and underway. 

 In the first situation the work is generally conducted at a specific location 

 and the support vessel requirements are minimal, calling only for adequate 

 deck space, power (unless a dedicated generator is brought aboard) and a 

 handling system. In the second situation the work task may require transits 

 many kilometers long where the support ship is required to stay within a 

 prescribed radius (foot print) above the vehicle which may be, for example, 

 inspecting a pipeline or cable. This type of operation is referred to as 

 "liveboating" and calls for a variety of support vessel capabilities. The 

 following discussion is addressed primarily to the liveboating situation. 



There is no industrially-operated ROV that works from a dedicated support ship. 

 One of the chief assets of an ROV is transportability, hence, it should be 

 able to operate from a vessel likely to be available at the work site. In 

 areas such as the Gulf of Mexico a typical 40 to 60m (130 to 197 ft) LOA 

 700 to 1000 metric tons displacement offshore supply vessel may be adequate. 

 In the North Sea the vessel might be 55 to 60m (180 to 200 ft) LOA. Cruising 

 speed is not important from an operational point of view; however, the economics 

 of transitting to and from the work site calls for speed in the neighborhood of 

 12 knots. The critical support platform characteristics are auxiliary power, 

 deck space, and maneuverability at low speed. 



2. 1.11. a Power 



Section 2.1.3 discussed the power requirements for ROV systems. Assuming that 

 the support vessel can provide requirements for a specific vehicle (not only 

 for the vehicle, but the launch/retrieval systems also if it is not supplied 

 by the ship) , then the next consideration is that the power supply not be 

 affected by surges in the ship's power, such as those which may occur when 

 additional power is required to maintain a particular bow heading at very low 

 forward speed. Occasions have arisen where a sudden surge of ship's propulsion 

 power was required which produced a voltage drop in the vehicle's power and 

 permitted it to drift off station. 



