However, the importance of the cable system, the expense of repairs, and 

 the increase in fishing operations all dictate that as much of the cable 

 be buried as possible, including repeaters. 



g. The system must be simple and reliable. 



This requirement is at odds with most of the others, which imply 

 a high degree of sophistication and complexity. In essence, this require- 

 ment constrains the selection of exotic techniques which oversolve the 

 problem at the expense of a complex system prone to nuisance breakdowns. 

 Certainly, the cable burial system will have to be sufficiently sophisti- 

 cated to perform well in a rather trying environment. 



An implication of this requirement is that the effort should lean 

 toward engineering development to extend and improve existing technology, 

 rather than to perform basic research to validate ''blue sky'' ideas. 



Specific Operational Requirements. 



a. The system must bury previously laid cable. 



This requirement results from operating with ships of opportunity 

 but is also important for other reasons. A cable-laying ship operates 

 at speeds to 8 knots, while a cable-burying operation proceeds, at about 

 1 knot. If the burier can bury cables only while they are being laid, the 

 cable-laying operation is inefficient, and the probability of the laying 

 operation being interrupted by adverse weather increases. Obstacles, 

 breakdowns, and deteriorating weather can be handled more easily if the 

 two operations are not being carried out at the same time. Burying pre- 

 viously laid cables will allow unburied cable systems which are in current 

 use to be protected by the burial system. 



Certain operational advantages result from a two-step operation as 

 well. For the installation of a high priority cable system, the cable 

 laying could proceed at 8 knots, and the system be made operational. The 

 cable could then be buried at a later date without having delayed the 

 cable system's use. 



Finally, the burial system's capability to pick up and drop a cable, 

 implied by this requirement, allows rapid abandonment of the burial oper- 

 ation if the weather worsens, eliminates the necessity of deploying and 

 retrieving the burial system with the cable threaded through the machine, 

 and allows burial of repair sections. 



b. The burier must be able to track the cable. 



Previously laid cables are not necessarily straight , so the burying 

 machine must sense changes in cable direction. The sensor must provide 

 information to the machine's control system and /or the support ship to 

 avoid damaging the cable or overturning the machine. 



c. The system must be able to bury spliced repair sections of cable. 



Even if a cable has not been in place for a long time, it may have 

 been damaged and repaired prior to burial. Older cables almost certainly 



