INTRODUCTION 



Seafloor cabling systems are being employed by the Navy in increasing 

 numbers. Their applications include power and communication transmission 

 to and from remote locations, acoustic research and development ranges, 

 and surveillance system trunk lines. The cable systems are quite vulnera- 

 ble to damage from commercial fishing activities, ships' anchors and other 

 natural and man-made hazards. Recent increases in bottom fishing activities 

 have produced a marked escalation of bottom-laid cable failures [1], re- 

 sulting in unreliable cable systems and a staggering increase in expendi- 

 tures for cable repair operations. In August 1974, the Civil Engineering 

 Laboratory (CEL) , realizing that the problem was worsening and severely 

 hampering Naval operations, proposed a program to provide a system which 

 would efficiently and effectively bury cables in the seafloor, eliminating 

 all but major natural hazards and intentional acts. 



The first phase of the deep ocean cable burial program was to identify 

 the techniques and equipment that are currently available to bury cables 

 and pipelines, both on land and underwater, and to define the operational 

 requirements that a deep ocean cable burial system must satisfy. With this 

 background information, viable hardware concepts were identified and com- 

 pared, and the most promising approach was selected. This work, sponsored 

 by the Naval Facilities Engineering Command, is summarized in this report. 

 In addition, recommendations are made which identify the research and 

 development required to produce a military cable burial system capable 

 of burying cables in seafloor sediments to a water depth of 6,000 feet. 



BACKGROUND 



Failures of bottom-laid cable systems, both military and commerical, 

 are attributed to both natural and man-induced phenomena. Natural failures 

 typically occur in shallow (0 to 20 fathoms) water near the shore end 

 of the cable and are caused by wave-, current-, and surge-induced motion, 

 resulting in abrasion and corrosion degradation of the cable protection 

 systems. Ship anchor drag also causes cable failures in shallow water. 

 Deep-water (greater than 20 fathoms) failures are caused almost exclusively 

 by scallopers and trawlers, with isolated failures attributed to turbidity 

 currents and ice scour. 



The specific threat to cable integrity to which this program is ad- 

 dressed is that due to fishing operations. Fishing trawls drag massive 

 ''otter boards'' or ''doors'' along the seafloor, one at each end of the 

 net opening, to keep the trawl nets open (Figure 1). These steel-edged 

 doors may weigh as much as four tons and penetrate a foot or two into the 



