also is shown is Figure 3. The predictions Include the effects of the drag impart- 

 ed by the remote sensor cables; the depressor is assumed to have a lift-to-drag ratio 

 of 4.0 The calculations indicate that a depressor force of 9 kN at 10 knots will 

 maintain a cable factor of safety of 2.7. For this depressor force, a towcable 

 wetted length of 920 m is predicted to achieve the maximum operational depth of 

 200 m. 



The ultimate selection of cable factor of safety must be based on judgment of 

 the relative importance of conflicting goals. A small factor of safety will reduce 

 usable cable life and increase the chances of cable breakage. An excessive factor 

 of safety (low tensile stress) at a given towing speed will decrease the towing depth 

 or require a longer towcable length. For the system under consideration, a large 

 factor of safety also will cause more undesirable variation in the relative vertical 

 separations of the remote sensors during cyclic control. If the towcable is properly 

 maintained and the towing tension is continuously monitored, a factor of safety of 

 2.7 at a speed of 10 knots should be adequate, although certainly not excessive. If 

 a higher factor of safety is desired, towing speed can be reduced without sacrific- 

 ing other performance parameters. With a design factor of safety of 2.7 at 10 

 knots, reducing speed to 8 knots will increase this margin to 4.2. 



A low-drag cable fairing such as manufactured by Fathom Oceanology, Ltd. in 

 Canada could be expected to substantially enhance towing performance. Calculations 

 indicate that, for the same towing tension, only 275 m of towcable would be required 

 to achieve a depth of 200 m. A towcable of this type, however, would make attachment 

 of remote sensors more difficult and also would require special and, therefore, ex- 

 pensive handling equipment. 



DESCRIPTION OF EQUIPMENT 

 Not including the CTD instrumentation and the associated remote sensor cables, 

 the towing system consists of four major pieces of equipment: the depressor, the 

 towcable, the two remote sensor mounts, and the control electronics. Guidelines 

 for operation and maintenance of the equipment are given in Appendix B. Design 

 drawings for the mechanical equipment and control electronics are contained in 

 Appendices C and D, respectively. The equipment is described below. 



