the wave damping characteristics and to relate its efficiency to a range of 

 wavelengths typical of coastal waters. Revised designs have been proposed. 



a. Western Canada Hydraulic Laboratories Investigations . Three models of 

 the A-frame floating breakwater (Fig. 106) were constructed at Western Canada 

 Hydraulic Laboratories to a scale of 1:23.4, representing prototype dimensions 

 of 15, 25, and 35 feet wide by 60 feet long. The framework of the break- 

 waters, which consisted of angles and channels of standard pattern, was dupli- 

 cated to the proper scale by forming thin metal plates. Anchor chains of 

 copper were used, representing a prototype chain weight of 11 pounds per foot 

 of length. The vertical timber wall was represented by 0.5-inch painted 

 plywood to prevent water absorption. Anchorage was provided by lead blocks of 

 sufficient weight to prevent dragging (sliding) under the most severe wave 

 conditions. The anchor chain length used in the model was approximately 2.5 

 times the water depth, which was 40 feet prototype dimension. 



NOTE 



variables 



Aluminum Cylbdtr 



THIN ALUMINUM PLATE 



PLYWOOO 



Figure 106. 



A-frame floating breakwater evaluated experimentally in 

 both a three-dimensional and two-dimensional wave basin. 



Rolling action of the breakwaters differed noticeably under various wave 

 conditions. When subjected to long waves, the roll was fairly symmetrical 

 about the longitudinal axis, coupled with the normal rise and fall. As 

 wavelengths decreased, the leeward pontoon tended to be displaced less than 

 the windward. This was most noticeable in the three-dimensional tests when 

 wavelengths were about equal to the breakwater width. The leeward pontoon at 

 times rotated on its axis, acting as a pivot which moved the windward pontoon 

 through an arc of 2 to 3 feet. A strong reflected wave was noted with each 

 breakwater, indicating an effective interference with the imposed wave. The 



157 



