Each breakwater model was evaluated in a three-dimensional wave basin by 

 anchoring with eight chains. A wave sensor was mounted on a movable rail to 

 obtain wave measurements over a system of coordinates on the lee side of the 

 breakwater. The measuring points covered a 50-foot area on each side of the 

 breakwater centerline and extended leeward a distance of 80 feet. After a 

 complete cycle of wave height recordings for each breakwater had been 

 obtained, the model was removed and the incident wave height at the same 

 measuring points (in the breakwater absence) was recorded. 



Instrumentation for measuring anchor stresses consisted of duralumin rings 

 in which strain gages were mounted to form one-half of an electronic bridge. 

 The duralumin rings were calibrated, then placed in position, forming the 

 terminal links at the breakwater end of the anchor chain, and adjusted to read 

 zero when completely load-free. The incident wave was then imposed on the 

 model, and each anchor force was recorded. 



The three Canadian caisson-type breakwater models tested reached their 

 maximum wave damping effectiveness of 55 to 60 percent with a wavelength of 50 

 feet. The width of the breakwater had no marked effect on the wave damping 

 effectiveness with wavelengths of 50 feet or less. These data indicated that 

 the breakwater effectiveness deteriorates rapidly for small ratios of break- 

 water width-to-wavelength (Fig. 49). Due to the low freeboard of the struc- 

 tures, the decks were constantly awash when wavelengths of more than 15 feet 

 with heights greater than about 2 feet struck the breakwaters. Generally, the 

 anchor forces were smaller for the wider breakwaters; hence, this substan- 

 tiated the previous conclusion that a part of the wave should be made to react 

 against other parts of the wave to produce a smaller net force on the anchor 

 system. This phenomenon occurs when the breakwater is at least half as wide 

 as the wavelength. The anchor forces measured during these three-dimensional 

 wave basin tests of the Canadian caisson floating breakwater are presented in 

 Figure 50. 



30 



20 



CTJ *v 



! 



S X 



. 



^ +J 





cU bo 





<D c 





Sh 0) 





pa ih 



' 1 



tw > 10 





o cd 





O 18' BREAKWATER 

 24' BREAKWATER 

 A 36' BREAKWATER 



j. ___| 



10 20 30 



Reduction in Wave Height 



Figure 49. Effect of relative breakwater width, W/L, on wave height 

 attenuation, Canadian caisson floating breakwater (after 

 Western Canada Hydraulic Laboratories, 1966b). 



86 



