of to 4 knots. At 4 knots, the fairing tended to tow in towards the propellers 

 and it was not feasible to tow above this speed. 



To carry out the tests to determine the vibration characteristics of the 

 faired system, the instrumented housings were replaced with hydrophones, as 

 shown in Figure 7. Two similar hydrophones were attached to an unfaired 

 5/8-inch (not shown in Figure 5) weighted line to measure the vibrations for 

 comparison with the faired system. The hydrophones were located at depths 

 of 50 and 100 feet in each system . Tests were made over a speed range of 

 to 4 knots and the hydrophone signals were recorded over the full speed 

 range . 



i 

 EVALUATION TESTS AT SEA 



The tests conducted in Chesapeake Bay resulted in information which was 

 applicable to full-scale arrays. Accordingly, an experimental full-scale array 

 for studying submarine radiated-noise patterns was first constructed and then 

 tested at sea off Key West, Florida. The purpose of these tests was to deter- 

 mine stability, towing characteristics, configuration, and acoustic performance 

 of the array. It was also desired to obtain information required for design 

 modifications for future arrays . 



The array used in the first sea tests is shown by the sketch in Figure 8. 

 It is composed of a 100-pound faired towing model, pressure gages, hydro- 

 phones, buoys, float material, and a network of cables. All three legs of the 

 system (horizontal and two vertical legs) are composed of 0.7-inch diameter 

 cable with 26 twisted pairs of conductors and a strength member. The inter- 

 mediate cables suspended from the horizontal leg are 0.3 -inch in diameter. 

 The horizontal leg is supported by flotation material. Hydrophones and depth 

 gages were located at the points indicated in the sketch. Junctions were pro- 

 vided for additional hydrophones and depth gages to be located every 100 feet 

 along the vertical legs. The system was towed over a speed range of to 

 3 knots while pressure measurements and hydrophone signals were recorded. 



On a subsequent sea trial, the array shown by the diagram in Figure 9 

 was used. The added 500-pound faired towing weight in the second system was 

 intended to provide greater depth and more vertical area in the loop formed by 

 the array. 



PRESENTATION AND DISCUSSION OF RESULTS 



The results of the shallow-water tests are presented in Figure 10 as dif- 

 ferences in relative noise level versus frequency for three of the test con- 

 ditions . Since the results with the fourth condition (simulated fairing with a 

 roughened surface) were approximately the same as those with a smooth sur- 

 face they are not presented. It maybe seen from Figure 10 that, for the very 

 low speeds (0. 1 to 0.25 knots), there are no significant differences in noise 



