and the average load per meter length of the breakwater for given 

 incident heights for the 8-module FTB in 4 meters of water and the 12- 

 module FTB in 4 and 2 meters of water are shown in- Figures 19 to 24, 

 respectively. In comparing the peak force to the average force for 

 each of the three conditions, it is noted that the peak force is the 

 same or only slightly higher for the 8 modules in 4 meters of water and 

 the 12 modules in 2 meters of water. However, when comparing the 12- 

 module structure in 4 meters of water the peak force is about 20 percent 

 higher than the average force; the peak force is the largest overall 

 force recorded. This indicates that for the same wavelength and wave 

 height, additional modules increase the peak force slightly. Since only 

 two breakwater lengths were tested, it is impossible to determine if this 

 trend will continue if the breakwater width is increased significantly 

 over the tested length of 12.8 meters. The peak forces presented in the 

 various figures represent the maximum force measured during the test, as 

 discussed previously. These forces usually occur when the motionless 

 breakwater is first subjected to wave motion. The relative velocity 

 between the water motion and breakwater is largest at this time. As the 

 mass of the breakwater increases, a larger force is required to initiate 

 movement of the structure and there is a longer time period before the 

 force levels off. 



In all cases, the larger the wave height and W/L ratio, the higher 

 the peak and average forcOo However, no strong steepness or period 

 effect was discernible in the data for either the peak or average force. 

 Plotting all the peak force data together (Figo 25) and the average force 

 data together (Fig. 26) allows conservative prediction curves to be drawn 

 through the upper parts of the data. These curves approach zero force 

 when the incident height approaches zero, as expected.. 



Since the peak force represents the situation when the breakwater was 

 initially at rest and then subjected to monochromatic waves, the maximum 

 force that would be calculated using the peakload curve would probably 

 be somewhat larger than the peakload that would occur in a train of 

 irregular waves. Therefore, a conservative force prediction for an FTB 

 would be to obtain the mooring force load based on the peakload curve 

 (Fig. 25). 



The anchor design depends as much on the bottom conditions as the 

 force applied and the anchor should be designed accordingly. Also, the 

 connection between the anchor and the mooring line should be such that 

 it allows maximum movement to prevent fatigue of the mooring line. 



Design of rear mooring lines and anchors was not investigated during 

 the study. However, limited data were collected with the four-module- 

 wide structure in 4 meters of water. These data show that with the waves 

 approaching normal to the structure, the rear forces were on the order of 

 5 to 10 percent of the maximum force obtained on the front anchor. Thus, 

 the rear anchor system should be designed for the largest force determined 

 by either the force of the largest wave coming from the shore or, e.g., 20 

 percent of the seaward force. 



32 



