Fig. k. Instrument section after potting 



Fig. 5- Instrument section bent around kh- inch diameter. 



group of connections being made. To each cable 

 lead to be used at this point a special single 

 conductor wire about 8 inches long is soldered 

 and the joint covered with shrinkable tubing. 

 This special wire is non-hosing and is insulated 

 with material compatible with polyurethane . The 

 diameter is sufficient to allow passage through 

 a hole in the cone and collar to the area immedi- 

 ately adjacent to the terminal assembly where 

 the preamplifier and hydrophone packages have 

 already been positioned on the cable. This lead 

 and a lead from the preamplifier package are 

 soldered together. Two such leads are required 

 for each preamplifier. Two leads from the oppo- 

 site end of the preamplifier are soldered to two 

 shielded leads from one end of the hydrophone. 

 A service loop to provide stretch length during 

 flexing is provided by rotating each lead l80° 

 around the center cable. The volume between each 

 component is filled with polyurethane. This 

 encapsulation positions the units on the cable, 

 provides a watertight seal and mechanical pro- 

 tection for the necessary connections and pro- 

 vides a flexible cushion between the units to 

 prevent interference during the flexing that 

 occurs as the assembly passes over a sheave or is 

 wound around a storage drum. To facilitate the 

 passage of the assembly over curved surfaces, a 

 tapered section is moulded at each end of the 

 package (Fig. K) . 



Polyurethane was used for all moulding appli- 

 cations . Of the large number of materials tested 

 it possessed, in addition to the desired physical 

 and electrical properties, the greatest ability 

 to bond to metal, rubber, fiberglass and PVC. It 

 is easy to handle, particularly if the material 

 is used in the frozen cartridge form, moulds can 

 be simply made and low temperature or room tem- 

 perature cures are reliable and easy to make. 

 Tests on the instrument bundle over a sheave under 

 load simulating the worst actual operating condi- 

 tions have shown that these compounds have very 

 good abrasion resistance in addition to their 

 flexibility. 



To provide array position information, tilt 

 indicators and magnetometer probes were included 

 in the array assembly. As many as five leads 

 were required for these instruments so that as 

 many as five holes were needed through the cone 

 and collar. Assembly procedures, however, were 

 similar to that used for the hydrophones and 

 preamplifiers . 



Instrument assemblies manufactured according 

 to the above procedures have been tested under 

 tensions of 1, 200 pounds while flexing over a 

 sheave kk inches in diameter (Fig. 5)- Minimum 

 time to failure has been about 200 cycles with 

 some sections surviving over 500 cycles before 

 lead failure. 



78 



