3. EQUIPMENT AND INSTRUMENTS 



91 



for deep casts, alternating current electric 

 drive cannot be used unless complex and ex- 

 pensive control systems are incorporated. 



An advanced type of oceanographic winch 

 (Fig. 30) specially designed for the purpose 

 is coming into use. The winch has electro- 

 hydraulic drive powered by a 15 HP con- 

 stant speed electric motor driving a piston- 

 type hydraulic pump. Control is exercised 

 by stroking the pump, i.e., varying the length 

 of stroke of the piston. The equipment is 

 capable of a line pull of 1,500 pounds at 300 

 feet per minute. The capacity of the winch 

 drum is 30,000 feet of %2-inch stainless steel 

 cable. The new winch is substantially su- 

 perior to the older types in that it provides 



greater line pull, increased retrieving speed, 

 improved control, more protection of equip- 

 ment afforded by the hydraulic system, and 

 several safety features. The most important 

 safety feature is the automatic overhauling 

 device which operates as follows: when the 

 line pull exceeds 1,500 pounds, the hydraulic 

 fluid is vented to a by-pass and the winch 

 overhauls at a slow speed until stopped by 

 the brake. This prevents closer approach to 

 the 2,200 pound breaking strength of the 

 cable and possible loss of an expensive group 

 of instruments or the cable which is also 

 costly. 



This is an intermediate size winch suit- 

 able for lowering small corers, cameras, Nan- 



FlGURE 30. — A modern electro-hydraulic oceanographic winch with a capacity of 30,000 feet of 5/32 inch 



wire rope. 



