Suspension and Cable Systems 



The all-nonbuoyant cable system and the system 

 using both buoyant and nonbuoyant cable will be discussed 

 together, since in many respects they are quite similar. 

 These two systems overloaded more during the initial part 

 of a run and took longer to stabilize than did the other 

 systems. This effectively reduced the amount of slack 

 time. Also, the two systems were not suitable for use in 

 very shallow water, since the nonbuoyant cable would drag 

 on the bottom. The stresses on the cable were also greater 

 for the nonbuoyant systems. 



The two remaining cable systems both use all- 

 buoyant cable. One of them uses the shock-cord suspension 

 and the other uses simply the inflated hose with no shock 

 cord. Both of these systems are very quiet and both reach 

 stability very quickly. The system without the shock cord 

 has the advantages of not needing careful adjustment of the 

 suspension system, and of permitting change in the hydro- 

 phone depth by simply changing the location of the suspen- 

 sion. In view of these features, the all-buoyant cable 

 system without the shock-cord suspension was selected for 

 general use. 



CONCLUSIONS 



A portable sound-pressure measuring system has 

 been developed and used in a variety of situations, with the 

 capability of measuring very low ambient-noise levels. 



High self-noise levels at frequencies less than 50 to 

 63 Hz are quite likely to be present if measurements are 

 made from a drifting ship and the cable is towed at the drift 

 velocity. These high levels are believed to be due to a 

 combination of flow noise and noise arising from cable 

 vibrations which impart accelerations to the hydrophone. 



These high self-noise levels can be satisfactorily 

 eliminated by using the slack-cable system described in 

 this report. 



33 



