a more compliant material to reduce the peak tensions, such as double-braided 

 nylon, can be used. 



b. Cost Estimate. For prototype field test planning purposes, Jones 

 (1980) provided cost estimates for installing a 90-foot-long pontoon barge for 

 a proposed sloping-float breakwater. The estimates reflect system definition 

 now available, including conventional drag-embedment anchors, and chain and 

 synthetic-fiber rope moorings. The uninstalled cost estimate of $6,000 per 

 front foot includes about 10 percent for moorings at a 30-foot water depth, 

 with the estimate based on the assumption that the average spacing between 

 floats would be approximately 3.5 feet. This spacing is determined by the 

 selected design of the moorings and connectors. The cost estimate allowed for 

 minor structural additions to the pontoon sections for mooring line attachment 

 points, for piping for ballasting and deballasting the individual pontoons, 

 and for interconnections between adjacent modules. 



Jones 1 (1980) cost estimate for the uninstalled sloping-float breakwater 

 contrasts significantly with estimates for present COE floating breakwaters. 

 The conventional type of floating breakwater usually adapted to semiprotected 

 regions cost about $1,500 to $2,000 per linear foot, but they are only effec- 

 tive wave attenuators for wave periods up to about 4 seconds. The NCEL con- 

 cept, and the requirements for the COE open-ocean operations, are considered 

 significantly effective for periods up to 7 seconds. This degree of protec- 

 tion increases effective working time enough to make the estimate attractive 

 for selected situations and environments. The estimated cost for 600 feet of 

 sloping-float breakwater (considered minimal for open-ocean operations) is 

 approximately $3.6 million. The maximum probable forces to which this struc- 

 ture will be exposed far exceed the forces induced by the 7-second design 

 wave conditions. The system simply cannot withstand these forces; hence, a 

 sloping-float breakwater installation must not be left unattended for long 

 periods of time, as is the case for semiprotected bays or harbors. 



V. SCRAP-TIRE FLOATING BREAKWATERS 



Used automobile and truck tires are accumulating at an estimated rate of 

 about 200 million yearly, with only about 10 percent recycled. This indicates 

 that about 2 million tons of material is added each year to an already immense 

 stockpile of existing scrap tires, conservatively estimated (Kowalski and 

 Ross, 1975) to exceed 2 billion in the United States alone. The seemingly 

 physical indestructibility of these abandoned tires has historically posed a 

 vexing problem in seeking pollution-free methods of disposal. Concerned with 

 the magnitude of this problem, the rubber industry and their research 

 scientists are constantly seeking new and innovative methods for utilizing 

 these wornout tires after they have served their initial purpose. 



Coastal engineers have long been interested in resilient energy absorption 

 mats for shore protection and harbor problem solutions, and scrap tires have 

 been used occasionally for revetment stabilization; however, it is not known 

 precisely who was the first to utilize scrap tires in a floating configuration 

 to dissipate wave energy before it reaches shore. Systematic investigations 

 of the use of scrap tires as floating breakwaters have been limited to the 

 past 20 years. Stitt and Noble (1963) developed and patented the "Wave-Maze," 



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