CONCLUSIONS AND RECOMMENDATIONS 



On the basis of experimental and theoretical investigations of typical 

 surface- suspended hydrophone systems, it is concluded that: 



1. Any movement of sensitive non-acceleration cancelling hydro- 

 phones such as the AX-58, whether due to cable vibrations or to hydrophone 

 oscillations, affects the acoustic signal in the low frequency range. 



2. By stabilizing the hydrophone with the addition of a shroud-ring 

 tail the very low frequency oscillations are substantially reduced for the range 

 of towing speeds which are usually encountered during submarine radiated- 

 noise measurements. 



3. Single hydrophone cables in a flow environment tend to vibrate 

 due to vortex shedding of the Von Karman vortex street type. The vibrations 

 of the single cables interfere with acoustic measurements in the lower end of 

 the frequency range of interest. In general, bundling a number of cables, 

 thereby increasing the effective size of the cylinder, decreases the frequency 

 of vibration below the range of interest. 



4. Fairing hydrophone cables reduces cable vibration, aids in ob- 

 taining greater operating depth and speed, and improves the stability of the 

 system . 



5. The configurations of arrays similar to the ones investigated 

 can be predicted with reasonable accuracy. 



6. To obtain maximum depth at speeds above one knot, vertical 

 cables in array systems must be weighted. However, this may increase the 

 acoustic interference. 



7. The overall towing attitude of the full-scale array is satisfactory. 

 Based on the foregoing conclusions, it is recommended that: 



1. Hydrophones in surface-suspended array systems be stabilized 

 to reduce the oscillations and vibrations. 



2. The vibratory motions of the array lines be reduced by fairing 

 methods . 



3. Further tests be made to determine the type of cable fairing most 

 suitable for these kinds of arrays. 



4. The amount of fairing required to eliminate or reduce cable 

 vibration should be determined either experimentally or theoretically. 



5. Techniques for improved fabrication, launching, and storage of 

 complete array systems should be investigated. 



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