Ratio of Wavelength-to-Breakwater Width, 

 .__■.! 2 3 



L/W 

 4 



0.7 



1 









APROXIMATE 

 "PROTOTYPE 





1 





1 



+ 





SYMBOL 



WAVE HEIGHT. 



Ft 









0.6 



- o 



+ 



a 





1 



2 

 3 

 4 





1 

 2 







Oo 



o 



+ 

 



a 

 o 



0.5 



- 





5 





I 2 







+ 



o 



A 



+ 



0.4 















% 



o 







0.3 













a 



+ 

 o 







■ 



0.2 



+ 











%4 



O 



o 



+ 







© 



Of 



•6 



+o 









- 



0.1 





o 



A 



A 













■ 



















PROTOTYPE 



LENGTH* 23.5 Ft 



1 





1 





i 



1 







1 



I 



20 30 



40 50 



Wavelength, 



SO 



70 



(ft) 



80 



90 100 



Figure 203. 



Effect of incident wave height, H • , and rela- 

 tive breakwater width, L/W, on transmission 

 coefficient, C t , for twin-pontoon floating 

 breakwater (after Chen and Wiegel, 1969). 



Tension in the mooring line generally consisted of two components: one 

 component caused by the rolling motion of the breakwater, the other caused by 

 the wave breaking directly on the structure. The breakwater was designed, 

 however, so that the maximum component of the two forces did not act on the 

 mooring lines simultaneously. The rolling axis of the system is above the 

 mooring point; when incident waves strike the breakwater, the rolling motion 

 of the body tends to release the tension in the mooring line. When incident 

 wave troughs reach the breakwater, the tension in the mooring line is caused 

 by the rolling motion. Because of the reflections from the breakwater when 

 wavelengths were 40, 60, or 80 feet, reflected waves tended to increase what 

 otherwise would have been designated as the incident wave height. When the 

 wavelength was equal to 50, 70, or 90 feet, the reflected wave tended to 

 decrease the incident wave height (Chen and Wiegel, 1969). 



3. Twin Water Chamber and Pontoon Floating Breakwater. 



Chen and Wiegel (1969) developed a variation of the twin-pontoon system 

 designed to take advantage of a fixed, perforated wall by decreasing the 

 striking force of the wave by decreasing the reflection area. Wave energy was 

 partially dissipated by the flow through the perforated wall, as previously 

 suggested by Jarlan (1960, 1965), Marks (1966), Marks and Jarlan (1969), and 

 Terrett, Osorio, and Lean (1969). The design (Fig. 204) has double perfo- 

 rated walls which form two 8. 5-foot-high water chambers, each with 5.5 feet 

 immersed. The distance from the front perforated wall to the second perfo- 

 rated wall is 4 feet; the distance from the second perforated wall to the back 



261 



