OCEANOGRAPHIC INFORMATION FOR SUBMARINE CABLES 1049 



preliminary information for the determination of the amount of cable 

 required, for system transmission planning and for studies of cable- 

 placing techniques. 



One of the fundamental requirements in cable laying is the deposit 

 of a sufficient amount of cable to cover irregularities of the bottom 

 ! without introducing dangerous suspensions and without laying a waste- 

 ful amount of excess slack. Satisfaction of this requirement will require 

 the most detailed possible knowledge of bottom topography, coupled 

 with knowledge of the kinematics of the cable laying process.^ 



A determination of required cable strength does not directly call for 

 an extremely accurate knowledge of bottom depth and contour. The re- 

 quired cable strength is determined by cable tension during recovery, 

 which is two or more times that experienced during laying. Although 

 the required strength is directly proportional to the depth, it is also 

 affected to a major degree by the ship speed, cable angle during recovery, 

 and the ship motion caused by waves. The ship motion can be controlled 

 to some extent by seamanship and choice of the time at which the re- 

 cover}^ is to be made. 



Further, the design strength of the cable is in large measure deter- 

 mined by the strength of available steel and the amount of steel that 

 can be accommodated in an economical over-all design. Thus, uncer- 

 tainties of 5 to 10 per cent in the maximum depth of the water on a route 

 would not affect the cable design. Yet, during a critical recovery situ- 

 ation, a more accurate knowledge of depth would be useful in planning 

 and executing the operation. 



The integrity of the cable will depend on the choice of materials to 

 withstand biological factors and wear on the ocean bottom. A companion 

 paper- discusses the resistance of likely cable-sheath materials to attack 

 by marine borers and bacteria. 



II. TOPOGRAPHY 



2.1 General 



Mapping the ocean bottom involves depth measurements coupled 

 with a knowledge of the location on the earth's surface of the points 

 at which these measurements are made. There exists a vast store of 

 data on the depths of the oceans taken by hundreds of observers and 

 expeditions over the past hundred 3^ears. It is not surprising that many 

 of these data are of questionable accuracy due to errors in navigation, 

 soundings, plotting, and interpretation. Thus, before existing data can 

 be used for the engineering of submarine cable systems, it is essential 



