TRANSMISSION LOSS ACROSS WAKES 



505 



SOURCE IN WAKE 

 EQUATION (10) 



50 100 ISO 200 250 300 



AGE OF WAKE IN SECONDS 



Figure 1. Sound transmission loss due to wake versus 

 age of wake. Ship IV, December 30, 1943, 15 knots. 

 Source beyond wake. 



type — two old destroyers of the 1916-1917 class, a 

 new destroyer of the Fletcher class, and two destroyer 

 escorts.' Wakes were laid at speeds of 10, 15, 20, and 

 25 knots. A 50-ft motor launch repeatedly carried the 

 projectors, mounted at depths of 6 and 7 ft, respec- 

 tively, across the wake, while the hydrophones were 

 suspended from the bow of the E. W. Scripps at a 

 depth of 10 ft, about half the depth of the wake (see 

 Section 31.3). Sound at frequencies of 3, 8, 20, and 

 40 kc was recorded both with the launch beyond the 

 wake and with the launch inside the wake; while 

 sound recorded when the launch was on the near side 

 of the wake provided reference values. 



By applying a correction for the measured average 

 transmission loss in the ocean, all sound levels were 

 reduced to a standard distance of 100 yd, for the 

 three cases of (1) source beyond wake, (2) source in 

 wake, and (3) no wake intervening. The difference 

 between case (3) no wake intervening and case (1) 

 source beyond wake was taken to be the transmission 



SOURCE BEYOND WAKE 

 EQUATION (H) 



10 IS 20 30 10 IS 20 



SPEED OF WAKE-LAYING VESSEL IN KNOTS 



Figure 2. Dependence of transmission loss on speed of 

 wake-laying vessel. 



loss for the source beyond the wake, or //„ as defined 

 in equation (3) of Section 32. 1 ; similarly, the differ- 

 ence between case (3) no wake intervening and case 

 (2) source in wake was taken to be the transmission 

 logs for the source in the wake. 



In the original paper, the results are reproduced in 

 separate graphs for each of the several vessels, speeds, 

 frequencies, and locations of the source; one of these 

 is reproduced in Figure 1. However, not all the possi- 

 ble combinations of the different parameters are 

 actually shown. Although not representing the best 

 fit for every single set of observations, the following 

 interpolation formulas are believed to represent ade- 

 quately most of the data. 



Source in wake H'^ = 2.4(w/)= - (4.8 ± l.Q)t, (10) 



Source beyond wake /fu, = 1.5(w/)^- (3.0 + lA)t, (11) 



where v is the ship's speed in knots, / is the frequency 

 of the sound in kilocycles and t is the time in minutes 

 which has elapsed since the passage of the screws or 

 age of the wake. No standard errors are assigned in 



