43 



The majority of ROVs are launched/retrieved over-the-side from a stiff-legged 

 boom. On a ship the boom is of a length such that it is approximately equal 

 to or exceeds the ship's freeboard. This arrangement prohibits the vehicle 

 from slamming into the ship if it is rolling. Only two vehicles are known 

 to launch over- the- stern , CONSUB 201 and ORCA . In this mode the procedure is 

 similar to that used by manned submersibles, in that, an A-frame is used to 

 lower/raise the vehicle to and from the water. The technique of launching 

 over-the-side is preferred since it keeps the umbilical as far away as is 

 practicable from the ship's screws. 



Generally the vehicle is operated abeam of its support ship such that the trend 

 of the umbilical can be seen by the ship's Master and the potential for fouling 

 in either the main propellers or the bow tnruster is minimized. 



Many vehicles are both launched and retrieved by a line other than the 

 umbilical cable. When launching, a quick release hook is used that is tripped 

 (released) by a lanyard on deck. For retrieval some operators prefer to man- 

 euver the vehicle on the surface to a point where the lift line hook can be 

 attached from a long pole aboard ship. The vehicle is then quickly retrieved 

 to the point where it is two-blocked to the crane boom and then swung aboard. 

 As described in Section 2.1.8, other operators prefer to marry (tape) a length 

 of lift line to the umbilical which, when it has reached the winch, is used 

 to bring the vehicle aboard. This procedure requires either a second winch 

 or windless for the lift line. Only in special circumstances is a swimmer 

 used to attach the lift line, no company routinely operates on the basis of 

 deploying swimmers. Most vehicle systems use a drum to store the umbilical 

 cable. In several instances, however, the cable is simply faked out on deck 

 or within a suitable container. 



Several manufacturers provide an ROV system which also includes a launch/retrieval 

 device designed specifically for its vehicle. One such system is shown in 

 Plate 2.1; it consists of a control unit, a deck umbilical, winch unit, armored 

 cable assumbly, winch skid assembly, deployment capsule (launcher) and the 

 submersible winch unit. The deck winch unit is capable of reeling in/out 

 at any speed between 2 and 37m (0 to 120 ft) and holds 305m (1,000 ft) of 

 armored cable. The entire system (including the RCV-225) weighs 2,131kg 

 (4,700 lbs) and occupies 4.6m3 (162 ft^) . According to the manufacturer. 

 Hydro Products, purging of the deck winch unit is all that is necessary to 

 meet U.S. Coast Guard explosion-proof requirements for operation in hazardous 

 gas environments . 



The most sophisticated launch/retrieval system is the U.S. Navy's Motion 

 Compensation Deck Handling System (MCDHS) used to deploy RUWS and its 7,010m 

 (23,000 ft) of primary cable. 



The MCDHS is a hydro-pneumatic motion compensation system with an active servo 

 control which strives to minimize acceleration of the boom tip. The primary 

 control sensor is a gimballed accelerometer at the boom tip. The servo control 

 system minimizes the signal from this sensor by requesting compensating action 

 from the MCDHS control valves. This results in a nearly zero vertical movement 

 of the boom tip relative to the ocean floor. A secondary boom angle signal 

 is incorporated which is used for boom centering and active cushioning near 

 the stops. 



