WES is presently conducting two-dimensional wave flume experiments on the 

 sloping-float breakwater concept. These wave tests on dynamically modeled 

 barges are being performed with the use of a spectral wave generator capable 

 of producing any desired frequency-energy spectrum. U.S. Army Engineer 

 District, Wilmington, is considering the sloping-float breakwater (along with 

 other floating breakwater concepts) for protection of dredging operations and 

 sand bypassing at Oregon Inlet, North Carolina. Current COE floating break- 

 waters are effective in wave attenuation for periods up to about 4 seconds in 

 semiprotected bays and estuaries; however, the open-ocean application such as 

 Oregon Inlet construction requires substantial wave attenuation for wave 

 periods up to 7 seconds. This requirement has initiated joint investigative 

 action between NCEL and COE. 



5. Performance Summary . 



Jones (1978) adapted the performance of the sloping-float breakwater for 

 solid (no clearance) breakwaters in a regular wave climate to predict break- 

 water performance in fully developed, local wind-generated seas represented by 

 the Pierson-Moskowitz spectrum. Figures 68 and 69 show the float length 

 required to reduce wave heights to levels associated with sea-state 3 (small 

 waves, crests beginning to break, foam of glassy appearance, occasional white 

 foam crests) for water depths of 30 and 45 feet, respectively, developed by a 

 reanalysis of Patrick's (1951) original laboratory experimental data. For a 

 spectrum peaked at 7 seconds and a water depth of 30 feet, Figure 68 indicates 

 that the significant wave height is reduced to 4 feet if the floats are 76 

 feet long, or to 3 feet if the floats are 98 feet long. The mass and shipping 

 requirements of the transportable sloping-float breakwater are highly depend- 

 ent on the float length, which must be selected on the basis of water depth. 

 A system constructed from a standard module design, such as the 28- by 90- by 

 5-foot pontoon, should be the minimal engineering development. 



a. Installation. Jones, Lee, and Raichlen (1979) considered a proposed 

 layout for an assembly of sloping-float breakwaters, and Jones (1980) advanced 

 the layout of Figure 70. It was envisioned that the floating modules would be 

 connected, temporarily held in position by tugs, and then attached to preset 

 moorings. The containers would be ballasted by flooding with seawater through 

 valves in manifold headers which could be opened in quick succession. The 

 rate of flooding would be controlled by the module size selected for the ports 

 and by valves in the air system. After flooding, the moorings would require 

 readjustment. Experiments and experience indicate that floats as short as the 

 90-foot pontoon produce a useful degree of wave height reduction for dominant 

 wave periods up to 7 seconds; therefore, manageable-size floats have open- 

 ocean application. Experimental evidence indicates that sloping floats are 

 most effective if the angle of inclination is less than about 20°. Thus, a 

 90-foot float would be most effective in water depths less than about 30 feet. 



An important area of investigation is the mooring system. Raichlen (1978) 

 obtained mooring force data on a dynamically scaled model of a typical pontoon 

 moored in regular waves. The mooring simulated the resistance of one double- 

 braided polyester rope, 8-inch circumference per each 28-foot-wide pontoon. 

 The maximum mooring line tension was found to be excessive for some of the 

 larger wave heights when the wave period was greater than 7 seconds. However, 



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