DYNAMICS AND KINEMATICS OF SUBMARINE CABLE 



1153 



Finally, from Fig. 15 we get for the distance along the cable to the touch- 

 down point 



3.8 Shea's Alternative Recovery Procedure 



The high tensions which result in the usual recovery operation require 

 slow ship speeds of the order of one knot or less if the cable is not to be 

 broken. One wonders if it is possible to mitigate these tensions and thus 

 speed the recovery process. J. F. Shea discovered that this can theo- 

 retically be done by allowing as to exceed 90°, thus establishing the 

 straightline configuration (Fig. 16). As in laying, the normal drag forces 

 in this scheme support the cable, rather than push down on it as in con- 

 ventional recovery. However, in contrast to the laying situation we have 

 Vt = Vc + V cos a. Thus Vt is the sum of Vc and V cos a instead of 

 their difference and Dt is not necessarily negligible. Furthermore, the 

 direction of Dt is now such as to increase rather than decrease the tension 

 over the wh value. Hence, instead of (2), a summation of forces along the 

 cable yields Ts = wh + DtL, and the tension at the ship can be consid- 

 erably higher than wh. A curve of T^ as a function of ship speed for cable 

 No. 2 is shown in Fig. 13 with the label "Shea's recovery method". This 

 has been computed for the case of haul-in speed equal to ship speed by 

 means of the above equation and (15). It is seen that the tensions com- 

 puted for this method of recovery, at least for the cable No. 2, are never- 

 theless considerably smaller than those which occur in the usual recov- 

 ery procedure. It would seem that the straight-line recovery technique 

 could fruitfully bear further examination, especially for application to 

 the recovery of long stretches of cable. 



Fig. 16 — The present and Shea recovery methods. 



