SHALLOW-WATER TOWING TESTS 



The shallow -water tests were conducted in the towing basins at the 

 Taylor Model Basin primarily to ascertain whether the interference in the 

 acoustic measurement systems was due to cable vibration or to hydrophone 

 oscillations . This preliminary investigation was intended to set the basis for 

 possible solutions of the problems affecting acoustic measurements. 



The initial tests conducted in the basin were made using AX-58 type 

 hydrophones, as shown in Figure 3a. A shroud-ring tail similar to that shown 

 in Figure 3b was attached to the hydrophone to minimize oscillatory motions. 

 Each hydrophone was towed on a 9/1 6-inch diameter, rubber covered, elec- 

 trical cable, as shown in Figure 4. The cable had a weight of approximately 

 0. 1 pound per foot in water and served as a conductor for the hydrophone signal. 

 The units were towed over a speed range of to 3 knots. 



Standard type cable fairing was not available for the size cable being used 

 in the basin tests. As a substitute measure, a simulated fairing made from 

 2-inch plastic tubing, was used for some of these tests. The tubing was placed 

 over the cable so that it was free to align itself with the stream and was tested 

 using the hydrophone with and without the shroud-ring tail. In an attempt to 

 further break up the flow around the cable and thus reduce vibrations, the 

 plastic tubing was coated with a cork mixture to roughen the surface. The system 

 with the coated tubing was also towed over the 0-to 3-knot speed range. During 

 each run, noise measurements were made in l/3-octave bands using a spec- 

 trometer and a sound- level recorder. 



OPEN-WATER TOWING TESTS 



The shallow-water tests did not provide adequate information for deter- 

 mining the towing configuration of the hydrophone array as well as the effects 

 of the use of greater cable scopes and standard cable fairing on cable vibration. 

 Consequently, in an attempt to obtain the additional information in an environment 

 having a minimum of background noise, tests were conducted in open water in the 

 Chesapeake Bay. A secondary purpose of these tests was to obtain design in- 

 formation relative to a full-scale hydrophone array. 



The tests in the Chesapeake Bay were conducted with the configuration 

 similar, to that shown in Figure 5 using a motor boat as the towing vessel. Two 

 50-foot sections of fairing were used as the main towline. The fairing was of 

 an airfoil shape (TMB No. 7) 4 made of a two-durometer ' rubber which normally 

 would enclose the towcable. The 50-foot sections were joined together by 

 junction boxes, as shown in Figure 6. Both at the extreme end and at the junc- 

 tion of the two sections an instrument housing was attached which contained two 

 pendulum angle indicators (one for longitudinal and the other for lateral meas- 

 urements). A 100-pound faired towing weight was attached at the deepest end 

 of the array to provide directional stability. 



The initial tows were made over the stern, but satisfactory measurements 

 could not be obtained because of propeller wake. The towing arrangement was 

 then modified to permit over-the-side towing. It was then possible to tow the 

 configuration and make pressure and angular measurements over a speed range 



