t 3 



U 2- 



Hj/L : 04—07 



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



Figure 21. 



Effect of relative submergence, d /d , and relative water depth, 

 L/d, on coefficient of transmission, C t , of single-pontoon 

 floating breakwater (after Ofuya, 1968). 



reach of the semiprotected Puget Sound about 60 miles southwest of Seattle. 

 The floating breakwater is to protect a small-boat marina which is being 

 developed in the eastern part of the harbor. The proposed marina is exposed 

 to short-period wind waves from the northwest clockwise to the north. The 

 significant waves from the exposed directions range up to 2.8 seconds in 

 period and 2.0 feet in height. Although model tests performed by Kamel and 

 Davidson (1968), Davidson (1971), and Nece and Richey (1972) provided data on 

 the wave attenuation capability of floating structures composed of tires, 

 spheres, or a rectangular float, these data were not directly applicable to 

 the East Bay Marina design because of certain site-specific conditions. 

 Carver's (1979) study objective became twofold when it was believed that the 

 wave attenuation could not be analytically predicted with sufficient accuracy 

 at the time. A hydraulic model investigation appeared to offer the best means 

 of accurately and reliably comparing the performance of potential floating 

 breakwater plans. Initially, the wave attenuating properties of four float- 

 ing breakwater cross sections were to be determined by two-dimensional flume 

 tests for a selected range of wave conditions. Secondly, based on the two- 

 dimensional test results and relative costs of the structures, the best plan 

 was selected for three-dimensional testing. The three-dimensional tests 

 investigated the combined effects of angular wave attack, structure alinement, 

 wave transmission, and wave diffraction around the exposed end of the break- 

 water. 



Tests were conducted at an undistorted linear scale of 1:10, model to 

 prototype. All the model test sections were designed and constructed so that 

 centers of gravity and buoyancy, draft, mass moments of inertia, and water- 

 plane moments of inertia properly simulated those of the prototype structures 

 under consideration. Although the prototype structures consisted of basic 

 units of polystyrene foam covered with a concrete shell and added ballast 

 that were posttensioned together, the model breakwaters were necessarily 



53 



