SUMMARY 



1. Water jet trenching is basically simple and proven technology, but it 

 requires more power than other trenching systems to excavate at a speed 



of 1 knot. Water jet trenching is particularly suited to burying repeaters 

 and cable anomalies. 



2. Trenching augers must rotate at approximately 5,000 rpm to trench at 

 1 knot and are susceptible to damage from rocks buried in the soil. 



3. Conventional (upmilling) trenching has a high resistance force, is 

 susceptible to damage when encountering buried obstacles, and the 1 -knot 

 speed requirement is in excess of normal maximum trenching speeds. 



4. Climbmilling trenching provides a very desirable propulsion assistance 

 force, but is susceptible to damage from buried obstacles, requires too 

 much power, and may be unsuitable for the high excavation rate resulting 

 from 1 -knot forward speed requirement . 



5. Vibratory plowing has been shown to reduce normal plowing resistance 

 forces by 90-99% on land, is relatively insensitive to damage from buried 

 obstacles, and has achieved speeds in excess of 1 knot in some land soils. 

 In addition, the vibration allows the plow to achieve and maintain maximum 

 penetration; thus, the burial machine can be made lighter. Vibration 



also aids in dislodging subsoil rocks. The power requirement is in the 

 middle of the acceptable range, and the system is basically uncomplicated. 

 Auxiliary devices must be employed to bury repeaters and cable anomalies. 



6. Towing for primary propulsion imposes unacceptable constraints on 

 the support ship. The ship must have adequate power to tow the system 

 and must maintain a precise heading and course while traveling at 1 knot. 

 This quality of control requires bow thrusters and, ideally, stern thrusters 

 as well as excellent navigation feedback between the ship and the burying 

 machine. Also, towing allows only gross course changes of the burying 

 machine. Towing via the umbilical cable may be employed as an auxiliary 

 propulsion means for a self-propelled burial system. 



7. The oscillating disk propulsion means is unproven technology, may 

 result in a cumbersome and complex system, and may lead to steering and 

 control difficulties. 



8. Track/wheel propulsion has excellent steering and control features, 

 may prove to have good slope-climbing and obstacle-climbing ability, and 

 requires nominal power. However, tracking depends on the seafloor soil 

 properties and may not allow selecting one configuration which will 

 perform in all soils. Generating thrust with tracks or wheels has not 

 been proven for seafloor operation. 



9. Thrusters (shrouded props) are proven in deep ocean use, and their 

 performance can be predicted since they depend on a known media (water) 

 for thrust. They can be controlled easily in both magnitude and direction 

 of thrust to provide excellent steering and control capabilities. Thrusters 

 lend themselves to direct drive with electric motors that reduces power 

 conversion losses, compensating for the inefficiency of the thrusters 

 themselves. 



44 



1 



