vz =-d f 



Figure 72. Definitive sketch of the two-dimensional model Wave-Maze scrap- 

 tire floating breakwater, one-quarter scale (after Kamel and 

 Davidson, 1968). 



To be effective, the depth of a floating breakwater must be deep enough 

 that little wave energy can be transmitted beneath it. The breakwater must 

 also have the mass and damping characteristics necessary to prevent it from 

 moving extensively so that it will not generate large-amplitude waves. To 

 fulfill the latter requirement, the floating breakwater must have large nat- 

 ural periods to compare with the wave periods to which it will be subjected. 

 Analysis of the test data indicated that the relative height to which the 

 breakwater extends above still water does not seem to affect the wave reflec- 

 tion coefficient, C , or the wave transmission coefficient, CL. This was 

 due to the high flexibility of the breakwater which moved extensively as if it 

 were a part of the water surface. At the same time, a large increase in the 

 relative penetration into the fluid, y/d, resulted in only a small decrease 

 in the coefficient of wave transmission. These data are presented in Figure 

 73, which shows the effect of initial wave steepness, H-/L, on the coeffi- 

 cient of transmission, C t , and in Figure 74, which displays the effect of 

 relative submergence, y/d, on the transmission coefficient, C t « 



b. Mooring Line Forces . Kamel and Davidson (1968) found that a conven- 

 ient way of studying the mooring line forces on the Wave-Maze model floating 

 breakwater was to determine the ratio of the maximum horizontal forces exerted 

 on the structure, f , to the maximum force that would exist in the case of 



total reflection from a vertical wall, ft- . The approximate order of mae- 



' u max rt ^ ° 



nitude of the maximum horizontal force exerted on the structure was determined 



by attaching a force meter to the mooring lines (Fig. 75). The variation in 



the ratio of the maximum force in the breakwater mooring lines to the maximum 



total horizontal force exerted on a vertical reflecting wall, f„/f<- , with 



the relative breakwater width, W/L, is shown in Figure 76; the model data 



are tabulated in Table 3. It was discerned that the forces on the breakwater 



mooring lines, f , are relatively small compared to the force due to total 



reflection of a vertical wall, ft- . For the one-quarter scale model scrap- 



' L max J 1 v 



tire Wave-Maze floating breakwater, the ratio of f /ft. did not exceed 0.29 



and 0.22 for the seaward and shoreward mooring lines, respectively. It was 

 projected that since forces in the seaward mooring lines of prototype struc- 

 tures are considerable, these types of floating breakwaters will be subject to 

 large drift if slack in the mooring lines is large. 



120 



