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5.9 TETHERED MAINTENANCE VEHICLE 



Exxon Production Research Company is developing a Tethered Maintenance Vehicle 

 (TMV) designed to perform observation and manipulative tasks on facilities and 

 equipment associated with a deepwater marine production riser system (Teers, 

 1979). The maintenance system consists of the TMV, interchangeable tool packages, 

 a launch/recovery system, a control van and auxiliary surface support equipment. 



The TMV is rectangular shaped with an open framework design. It measures 2.1m 

 (7 ft) high, 2.4m (8 ft) wide and 5.7m (IS^a ft) long, and will weigh approximately 

 11,793kg (26,000 lbs). Ten thrusters will maneuver the vehicle, these are 

 powered by two lOOhp hydraulic pumps which also power the tool packages. Two 

 2200 VAC, 3-phase electric motors drive the hydraulic pumps and they receive 

 their power from a surface generator through an umbilical cable. Additional 

 power for all vehicles and tool package subsystems is provided through separate 

 conductors in the umbilical where a transformer in the TMV's distribution system 

 transforms 500 VAC, 3-phase to 120 VAC, 1-phase power. Five TV cameras constitute 

 the optical viewing system. The TMV also contains a station-keeping system 

 for tasks that do not require extensive shifting of pay load. A variable buoyancy 

 system can accommodate up to 1,814kg (4,000 lbs) of payload. 



A guidance system receives target information from transponders mounted on the 

 riser. The system permits the TMV to close and dock with the desired 

 riser attachment point. Once at the desired attachment point the tool package 

 attaches the system to the riser for performance of the maintenance task. 

 Since the hydraulic thrusters produce considerable noise, a composite noise 

 signature of the TIW hydraulic components was prepared which will be used to 

 design the guidance systems acoustic components to assure that they will not 

 interfere with the hydraulically-generated noise. 



Three tool packages have been designated: 



Hose Replacement Tool Package - to replace production hoses weighing up 



to 1,814kg (4,000 lbs) in water. 



Swivel Replacement Tool Package - to replace flowline swivels weighing 



up to 4,762kg (10,500 lbs) in water, and a 



General Purpose Tool Package - to perform maintenance tasks such as 



inspection, cleaning, anode replacement, and buoyancy module replacement. 



Each tool package can be rigidly attached to the riser by three attachment arms 

 which also provide the initial alignment. A force-feed-back manipulator on 

 each package will perform all manipulative tasks. 



Two modes of TMV operation are envisioned: a free-flying mode and a suspended 

 mode. According to Teers (1979), the techniques employed will be as follows: 



"When operating in the free-flying mode the TMV will be capable of 

 supporting a 1,814kg payload while moving freely in the water to 

 the work site. During this operation, a cable depressor (clump weight) 

 will be installed on the tether cable. The cable depressor will 



