2. Basic Groupings of Floating Breakwaters . 



The group of prismatic structures (single-pontoon, double-pontoon, cata- 

 maran, Alaska-type, or variations thereof) contains the simplest forms of 

 floating breakwaters. This prismatic form offers the best possibilities for 

 multiple use as walkways, storage, boat moorings, and fishing piers. For the 

 pontoon-type breakwaters, several factors in addition to mass seem to contrib- 

 ute to their performance. The radius of gyration and the depth of submergence 

 appear to significantly influence the attenuation characteristics. Further- 

 more, as the ratio of breakwater width-to-wavelength increases to values 

 greater than 0.5, the wave attenuation features of the structure not only 

 improve markedly, but the net result of the forces on the mooring and anchor- 

 ing system becomes substantially less. This occurs because the wave dynamics 

 are exerting forces on a part of the structure in a direction opposite to 

 those forces on other parts of the breakwater. The design of the catamaran 

 and double-pontoon systems attempts to combine relatively large mass and large 

 radii of gyration, thereby increasing the stability and performance of the 

 structure. 



The sloping-float breakwater concept is a wave barrier that consists of a 

 row of moored, flat slabs or panels whose mass distribution is such that, in 

 still water, each panel has one end resting on the bottom and the other end 

 protruding above the water surface. The U.S. Army Corps of Engineers has a 

 potential requirement for such a mobile breakwater system to provide partial 

 protection to dredges and work boats involved with the construction of coastal 

 engineering features in the nearshore zone of exposed open-ocean coastlines. 

 The wave climate in these regions can easily approach heights up to 8 feet 

 with periods up to 7 seconds. An increase in effective working time can be 

 accomplished by widening the wave window used by dredges and barges, which 

 reduces the wave energy in the sheltered region. Initial data on wave trans- 

 mission indicate that sloping 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. 



Coastal engineers have long been interested in resilient, energy- 

 absorption systems for shore protection, and the use of scrap tires for 

 floating breakwaters or other purposes have been investigated intermittently 

 for the past 20 years. Three basic designs constitute those which have 

 received the greatest attention from an experimental standpoint. A geometric 

 assembly configuration known as the "Wave-Maze" has been patented, and the 

 Goodyear Tire and Rubber Company has investigated extensively the use of 

 modular building-block elements formed by securing together bundles of tightly 

 interlocked scrap tires. Another concept known as the "Wave-Guard" uses 

 massive beams or poles onto which the scrap tires are threaded. 



Because of the availability of timber in many parts of the United States 

 and Canada, log structures have been used to protect harbors and boat anchor- 

 ages. The Canadian Department of Public Works developed and evaluated a 

 floating breakwater concept of circular cylinder design (the A-frame) which 

 incorporates a vertical wall for supplemental attenuation purposes. It 

 appears the effectiveness range of this concept can be significantly increased 

 by a large increase of its radius of gyration involving only a slight increase 

 in the mass of the structure. 



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