for the slope of the mooring line since the difference between the hori- 

 zontal and slope force components is negligible for the slopes tised) . 



4. Discussion of Results . 



a. Transmission Coefficient . Plots of the transmission coefficient, 

 K^, versus the breakwater width to wavelength ratio, W/L, are shown in 

 Figures 15, 16, and 17 for the 8-module FTB in 4 meters of water and the 

 12-module FTB in 4 and 2 meters of water, respectively. Ranges of inci- 

 dent wave heights are indicated by the legend symbols. 



Generally, the data show that as W/L increases the transmission 

 coefficient decreases. As expected, the transmission coefficient is 

 asymptotic to unity as W/L approaches zero. Also, for the same value 

 of W/L, as the incident wave height increases, the transmission coeffi- 

 cient decreases slightly. There is considerable scatter in the data for 

 W/L values less than 0.40. This is because the incident wave height was 

 usually small and was only 2 to 4 centimeters greater than the transmitted 

 height. Thus, a small change in the measured transmitted height causes a 

 large change in the value calculated for the transmission coefficient. 



For each of the test sections, minimum measured values obtained for 

 K^ were 0,7 for a W/L of 0.7 for the 8-module FTB in a 4-meter water 

 depth, 0.5 for a W/L of 1.1 with a 12-module FTB in a 4-meter water depth, 

 and 0.3 for a W/L of 1.35 with a 12-module FTB in a 2-meter water depth. 



Comparing the data from the 8-module FTB (Fig. 15) and the 12-module 

 FTB (Fig. 16) for the same water depth, transmission coefficients for the 

 12-module FTB appear to scatter less than the 8-module FTB for given wave 

 heights. Also, the 8-module FTB appears to be more efficient in reducing 

 wave transmission than the 12-module FTB for the same W/L ratios. How- 

 ever, closer examination shows that for the same W/L ratios, the inci- 

 dent wave heights were larger for the 8-module FTB data than with the 

 12-module FTB. Thus, as previously noted, for the conditions tested the 

 larger the height, the better the FTB attenuates waves. 



A comparison of Figures 16 and 17 (12-module FTB's in 4- and 2-meter 

 water depths, respectively) shows that for the conditions . tested the 

 water depth does not appear to influence the transmission coefficient. 

 This observation is contrary to the expectation that as more of the water 

 depth is taken up by the breakwater section, the wave attenuation should 

 increase. 



By plotting all the transmission data on one figure (Fig. 18) , a 

 design curve can be drawn which predicts the transmission coefficient 

 for a given breakwater width to wavelength ratio. The curve is based on 

 data having W/L ratios up to 1.4, wave heights up to 140 centimeters 

 (4.6 feet), and water depths of 4 meters or less. 



a. Mooring Forces . Two measures of the mooring force (peakload and 

 average load) were obtained for each of the test conditions. The peakload 



27 



