Stewart and Poudrier 



relatively shallow depths and at speeds of up to twelve knots, others 

 are used "on station" while the ship is hove to and may be lowered to 

 extreme depths, and some are used in conjuntion with moored buoy 

 systems. Each of the three types requires a different approach in 

 "fail-Safe" development, and different items of equipment now in 

 various stages of development will be applied. 



The first hardware item to be described, although not the first to be 

 completed, is a simple mechanical device to prevent loss of instrument 

 by two-blocking, which has been the. most frequent cause of losses and 

 probably the most costly. Some of the instruments lost in this manner 

 have replacement costs of around $20,000, to which must be added the 

 aforementioned attendant losses in ship time, etc. At first glance it 

 would appear that two-blocking is inexcusable, since if the winch 

 operator is attentive he should always stop the winch before the 

 instrument is brought up against the block. We must remember that if 

 an instrument has been lowered to extreme depths it may normally 

 require an hour and a half to hoist it to the surface, but only 

 another four seconds to hoist it from the surface to the block. Thus 

 inattention of less than one-tenth of one percent of the hoisting time 

 may be enough to cause loss of an expensive instrument. When we 

 consider that the sea-state and visibility conditions are not always 

 ideal, it is not too surprising that some instruments are two-blocked. 



The solution offered is to assume that occasionally instruments will 

 be two-blocked and cables broken, but to have ready a mechanism that 

 will catch tlie instrument before it can fall back into the sea. As 

 shown on the slide, the device which has been developed and successfully 

 tested consists of a "V" shaped bail attached to the standard meter 

 wheel and a special cable terminator for the cable, with the instru- 

 ment itself supported by a chain about eighteen inches below the 

 terminator. Tlie normal position of the bail is against the wheel, 

 where it is held by shock cords on either side. IVhen hoisted too far, 

 the terminator pushes the bail upward and passes through the wide part 

 of the "V", then strikes against the top of the block. At this point 

 the cable parts and the terminator drops back, but since the shock 

 cords have returned the bail to its normal position, the terminator 

 cannot pass through the small end of the "V". The instrument is caught 

 and remains suspended by the chain. Simple, inexpensive to build, and 

 easy to install, this device has been well received by NAVOCEANO oper- 

 ating personnel and is now being installed on AGOR and AGS ships. A 

 series of tests conducted in the environmental laboratory of the 

 NAVOCEANO Instrumentation Department and aboard USNS SANDS showed 

 sixteen successive catches and no failures to catch a simulated 300 

 pound instrument package. Statistically, this indicates with a confi- 

 dence of ninety percent a probability of success of eighty seven 

 percent in actual use. Continued testing might improve this figure 

 somewhat, but certainly it is an improvement over the former 100 per- 

 cent certainty of loss of the instrument if two-blocked. The 

 terminator tested was designed for use with 4-H-O cable (four 

 conductor) and uses a low temperature potting solder having a melting 



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