56 



2.2 BOTTOM-CRAWLING VEHICLES 



Vehicles in this category are primarily designed to perform a specific work 

 task. A listing of bottom-crawling vehicles is presented in Table 2.5, 

 individual specifications are contained in Appendix D. It is apparent from 

 Table 2.5 that the number of bottom-crawling vehicles is much less than the 

 free- swimming, tethered ROVs. Also, bottom-crawling vehicles are all operated 

 by the same company responsible for their construction. Significantly, except 

 for one instance, all bottom-crawling vehicles are industrially-oriented, 

 and this orientation is overwhelmingly directed toward offshore oil and natural 

 gas activities. 



2-2.1 Functions 



Bottom-crawling vehicles are designed to satisfy one of the following functions: 

 Pipe trenching, cable burial, bulldozing/dredging, and general (inspection/ 

 manipulation) work tasks. 



Pipe trenching is the predominant work function. Present capabilities permit trench- 

 ing of 400 to 1,200mm (16 to 48 in.) diameter pipe to a maximum of 2 . 5m (8.2 ft) in 

 water depths of 500m (1,640 ft). All vehicles but one discharges the trench 

 cuttings to the side of the trench. The exception, TM 102, discharges the 

 cuttings to the stern of the machine to act as backfill. 



Two vehicles are designed for cable burial, SEACAT and TALPETTA. In both 

 instances the trench dug is approximately Im (3 ft) deep. SEACAT is not a 

 true ROV since it relies upon a diver or a manned submersible to control 

 its movements and work functions once it is on the bottom. 



Bulldozing and dredging tasks are similar to those encountered on land. The 

 commercial success of these vehicles is uncertain. Three bulldozers have 

 been constructed, but it is not clear whether or not they have been used 

 commercially. 



Four general-purpose vehicles have been constructed; all but one are directed 

 toward the commercial market. The exception is RUM II which was built with 

 U.S Navy funds, but it has been inactive for the past six years. Typical 

 work tasks these vehicles purport to accomplish in the view of SEABUG I's 

 operators, are: Cable burial, pipeline inspection, debris mapping/clearance, 

 bottom route surveys, valve opening/closing, hydro couple installations, and 

 site investigations. These vehicles have only been available for commercial 

 operations within the past two years, consequently, their actual at-sea 

 utilization is still limited. 



2.2.2 Operating Depths 



Range Average 



Trenching Vehicles 46-650m 190m (623 ft) 



Cable Burial Vehicles 46-200m 123m (404 ft) 



Bulldozers 7-60m 42m (138 ft) 



General Purpose Vehicles 305-1, 877m 1,184m (3,885 ft) 



