Selection of Cable Size and Downforce 



Since we have now chosen the basic configuration, and 



have determined that the minimum value r^ is 42 x 10"^ 



sec^/ft for the 5000-foot depth, the selection of cable size 



becomes a matter of balancing requirements for a reasonable 



upper limit on the towing speed against the required size of 



electrical conductors and the practical problems of handling 



the system. Figure 1 shows the cable size and downforce 



required as a function of the maximum speed of tow, the down- 



T 

 force being obtained from the value ^ = 1,14 x 10® ^§- , 



corresponding to the minimum value of r^ , Note that, at the 



maximum allowable speed corresponding to the cable size 



selected, the cable length and horizontal distance of the 



bottom end from the tow point remain the same: namely, 



6200 feet and 3500 feet, respectively. 



Upon examination of Figure 2, it becomes evident that 

 the required cable size and downforce increase rapidly with 

 increase in speed. This is due, of course, to the fact 

 that the hydrodynamic forces acting on the system increase 

 as the square of the speed. If we adopt the position that, 

 in consideration of difficulty in handling and system costs, 

 it is desirable to keep the cable size as small as possible, 

 then the required size of electrical conductors becomes the 



22 



