The influence of wave steepness is most readily detectable for longer 

 waves (e.g., L/B larger than 2) and may be important at low water depths. 

 For L/B = 2.9 and D/d = 0.51 (Fig. 35), the value of C t decreases dramati- 

 cally from 0.9 to 0.4 as H/L increases from 0.007 to 0.028 (refer also to 

 Fig. C-7 in App. C) . The data in Figures 34 and 36 apply to the PT-1 module, 

 which has a pipe spacing of G/D = 3.3, aspect ratio of B/D = 12, and beam 

 B = 12.2 meters. These conditions may not be altered greatly without also 

 influencing the wave transmission characteristics. For example, the design 

 curves of Figure 36 may not apply to a structure with a much larger beam, 

 e.g., B = 24 meters (i.e., or B/D = 24). Until further data on the importance 

 of B/D are obtained, it is suggested that the PT-1 wave transmission design 

 curves of Figure 36 be limited to beam dimensions in the range from 9 to 15 

 meters. Such information has been recently provided in Harms, Bishop, and 

 Westerink, 1981. Existing data from small-scale experiments (Harms, 1979) 

 indicate that the transmission curve for D/d = 0.22 does not change signifi- 

 cantly as the water depth increases. For deepwater applications with D/d 

 less than 0.2, it is therefore suggested that the D/d = 0.22 curve be used for 

 design purposes, at least until further data become available. In addition, 

 curves should not be extrapolated beyond the range of data shown (i.e., 

 L/B > 4.5 and 3.0). 



b. PT-2 Breakwater . Wave transmission data for the PT-2 module (con- 

 structed of automobile tires and telephone poles) are shown in Figures 37 and 

 38, with design curves given in Figure 39. The behavior of the PT-2 module is 

 very similar to that of the PT-1 module, although a decrease in wave attenua- 

 tion performance is indicated, at least at the larger water depths considered 

 in Figure 40. It was observed that the influence of wave steepness H/L is 

 again particularly apparent at the lower water depth (D/d = 0.33, Fig. 38) and 

 large values of L/B. The actual H/L values associated with each data point 

 are given in the appendixes. Again, curves should not be extrapolated beyond 

 the range of the data shown (i.e., L/B > 4.5 and 3.0). 



E O.60 



D/d = 0.14 



-!—+—* 



x/* 



LEGEND 



(H/L) I0 2 

 * 0.6 lo 1.9 

 o 2.0 lo 6.0 

 x 6.0 1oll.2 



PT-2. MS-3 



0.50 1.00 1.50 2.00 2.50 3.00 3,50 4.00 4.50 



Relative Wavelength (L/B) 



Figure 



37. Wave transmission data for PT-2 breakwater 

 (d = 4.7 m). 



40 



