in diameter and approximately 540 mm long is required for the CTD electronics. A 

 single COAX conductor or an equivalent set of conductors is required in the tow- 

 cable to transmit power and receive signals for the CTD; depth control functions 

 should be provided by separate conductors. 



The two remote sensor units will be positioned at various locations along the 

 towcable. Maximum vertical separations from the depressor of 20 m and 10 m are re- 

 quired. Ideally, the vertical separations, relative to the depressor, should re- 

 main constant during cyclic depth control. The remote sensor units should be easily 

 removable from the towcable to facilitate handling and repositioning. 



PRELIMINARY DESIGN CALCULATIONS 



A sketch of the general towing configuration is shown in Figure 1. An open 

 loop configuration for the cables leading from the depressor to the remote sensors 

 was selected as the only practical means of allowing variable positioning of the 

 remote sensors. The remote sensor cable loops, however, will add substantial drag 

 to the system. This extra drag will increase the variations in the remote sensor 

 vertical separation during cyclic depth control; it also will increase the local 

 stresses in the towcable at the attachment points as well as cause an increase in 

 the overall towing tension. 



Preliminary calculations were preformed to establish the length and tension of 

 the remote sensor cables, the maximum length and tension of the towcable, and the 

 maximum depressor force. Details of the calculations are presented below. A more 

 complete set of performance predictions based on the selected towing equipment is 

 presented in Appendix A. 



REMOTE SENSOR CABLES 



1 A 

 Calculations were performed to determine the remote sensor cable length for 



minimum cable tension. A cable diameter of 13 mm was assumed. This diameter should 



provide adequate area for both electrical conductors and a suitable strength member. 



Also, the cable was assumed to be faired over its entire length with ribbon fairing 



to prevent excessive strumming. Normal and tangential hydrodynamic loading func- 



2 

 tions determined from basin experiments, with the tangential function multiplied 



*A complete listing of references is given on page 79. 



2 



