the sea floor. This alteration would increase the depth range in which a 

 float of a given length can be used. 



1. Users and Applicability . 



a. U.S. Army Corps of Engineers . The COE has a potential requirement for 

 a floating breakwater system to protect dredges and work boats involved in 

 coastal engineering construction in the nearshore zone of exposed coastlines. 

 The wave climate in these regions far exceeds the wave climate which floating 

 breakwaters are generally intended to attenuate (4-foot-high waves with up to 

 4-second periods, the wave climate of semiprotected bays and lakes). An 

 increase in effective working time can be accomplished by increasing the wave 

 window for dredges and barges by reducing the energy of waves substantially 

 larger than commonly encountered in sheltered regions. 



b. U.S. Navy. The Navy has a requirement for a ship-transportable break- 

 water to be used in conjunction with the Container Offloading and Transfer 

 System (COTS) being developed by the Naval Facilities Engineering Command 

 (Jones, 1978). In this concept, a container ship moored in exposed locations 

 offshore could have cargo expeditiously offloaded and transferred ashore. 

 These operations occur in water depths ranging from 20 to 60 feet or more. 

 Sloping-float breakwaters are being considered for protecting small, moored 

 craft and work platforms where waves with periods as small as 2 or 3 seconds 

 can be troublesome. The U.S. Navy is currently interested in a hollow, steel 

 barge adaptation (a pontoon barge or causeway section) which appears to have 

 acceptable dimensions and mass. These barges can be ballasted by flooding 

 compartments with seawater to provide the appropriate mass distribution. This 

 system requires mass that would not have to be transported to the desired 

 site, as the ballast water may account for more than three-fourths of the 

 total mass. The installation procedure currently under investigation is to 

 assemble floating (unballasted) modules on the surface and then, by venting, 

 flood the shoreward end of each float until the lower end rests on the bottom 

 and the upper end settles to the desired freeboard level. 



Preliminary experimental wave transmission data indicate that floats 90 

 feet long reduce the significant height of local wind-generated waves by more 

 than 50 percent when the dominant wave period is less than about 7 seconds and 

 the water depth is less than about 30 feet. Thus, pontoons, barges, or cause- 

 way sections may be considered for such ocean applications. Jones (1980) 

 estimated that an assembly of 30 such pontoon structures (each 90 feet long by 

 21 feet wide by 5 feet deep) could be carried on the hatch covers of a LASH 

 barge. This assemble would form a sloping-float breakwater with a sea-to- 

 shore dimension slightly less than 90 feet and an axial length of about 700 

 feet, which is considered sufficient to shelter a localized area for naval 

 operations. In water depths greater than 30 feet, floats would have to be 

 longer than 90 feet to maintain the same performance; e.g., in a 45-foot water 

 depth the float should be about 110 feet long. The Naval Civil Engineering 

 Laboratory is continuing research in this area with interest centered on wave 

 transmission and mooring forces for arbitrary float properties, water depths, 

 wave characteristics, and mooring system properties. The operational charac- 

 teristics of sloping-float breakwaters through full-scale open-ocean experi- 

 ments are being investigated. 



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