0.7 



0.6 



I 0.5 



c 



0.4 



0.2 



tWt". 



id = 2 



^7-7-77-7-77-7-7-7-7-? 7 ~. 



0-06 



^•06 



O-0G5 



/fio.065 (wave steepness, H./L) 



075 J-0 I 25 1-5 1-75 



Ratio of Wavelength-to-Water Depth, L/d 



Figure 105. Effect of relative water depth, L/d, and initial 



wave 



on transmission coefficient, C t , for 



twin-cylinder floating breakwater (after Ofuya, 1968). 



In a practical application of the twin-cylinder floating breakwater, the 

 most economical filling fluid would be water. Ofuya (1968) found that the 

 oscillation characteristics of the structure, and hence its wave damping per- 

 formance, was influenced by properties such as density and viscosity of the 

 filling fluid. With filling fluid of a higher viscosity than water, the 

 amplitude of oscillation was reduced considerably; with both cylinders filled, 

 the stable range of the structure was increased. Both factors tend to 

 increase the range of effectiveness of the twin-cylinder floating breakwater. 

 At a model-to-prototype scale of 1:16, each cylinder corresponds to a proto- 

 type dimension of 6 feet in diameter. For an arbitrarily defined limit of 

 wave transmission, C t = 0.5, the twin-cylinder floating breakwater would be 

 effective as a breakwater for deepwater waves of lengths up to about 40 feet. 

 In its submerged position, the twin-cylinder breakwater appears to be an 

 esthetic structure (Ofuya, 1968). Application of the structure to protect 

 locations exposed to deepwater waves would depend, therefore, on economic 

 considerations. Neither field tests nor prototype-scale investigations have 

 been conducted of this concept. 



3. A-Frame Floating Breakwater . 



A floating breakwater of the A-frame, pontoon-type (designed by the 

 Department of Public Works, Canada) has been in field service at Lund, British 

 Columbia, Canada, for several years, and has performed efficiently under all 

 wave conditions encountered at this site. Both Western Canada Hydraulic 

 Laboratories (1966a) and Ofuya (1968) conducted a series of tests to evaluate 



156 



