With the continually increasing ownership of pleasure craft, available 

 mooring spaces have been depleted in many locations. Escalating construction 

 costs and environmental constraints require alternative considerations to the 

 traditional fixed rubble-mound structure for harbor development. Many needed 

 facilities, particularly in Alaska, are so small and serve so few vessels that 

 large expenditures of funds cannot be justified. Additionally, at many of 

 these locations, site parameters such as deep water or poor bottom conditions 

 necessitate a floating structure. Research engineers and scientists recog- 

 nized the potential for floating breakwaters in certain areas, and research 

 interest has accelerated in recent years. This has also served to stimulate 

 theoretical analyses of floating structures subjected to dynamic environments, 

 as well as the more basic and fundamental physical hydraulic model approach to 

 the evaluation of various conceptual models. Computerized mathematical models 

 developed recently have produced quantitative theoretical results that compare 

 quite closely with results of experimental model investigations and prototype 

 monitoring efforts. 



2. Floating Breakwater Applicability . 



Permanently fixed breakwaters (rubble-mound or precast units) provide a 

 higher assurable degree of protection than floating breakwaters; however, they 

 are very expensive to construct. In water depths greater than about 10 feet, 

 a fixed breakwater may not be competitive costwise with a floating breakwater 

 (depending on the incident wave period). Floating breakwaters provide less 

 protection, but they are less expensive and are movable from one location to 

 another as required. It may be relatively easy to fabricate a floating break- 

 water at a site where a rigid bottom-resting gravity structure would be com- 

 pletely infeasible (water depth greater than about 30 to 40 feet, or unstable 

 foundation conditions). 



Several major points exist in the consideration of a floating breakwater. 

 The cost of a floating system is only slightly dependent on water depth and 

 foundation conditions. While the construction cost of a fixed rubble-mound 

 breakwater increases exponentially with depth, a floating breakwater requires 

 essentially the same structural features regardless of the water depth (except 

 for mooring arrangements). The interference of a floating breakwater with 

 shore processes, biological exchange, and with circulation and flushing cur- 

 rents essential for the maintenance of water quality is minimal (again depend- 

 ing on the incident wave period). The planform layout can be changed to 

 accommodate changes in either seasonal or long-term growth patterns. Floating 

 breakwaters appear to have greater multiple-use potential than fixed struc- 

 tures (they can be used as boat docks or boat mooring locations, and also 

 serve as walkways). 



Floating breakwaters, however, have some disadvantages which must be 

 weighed in their evaluation. The design of a floating breakwater system must 

 be carefully matched to the site conditions, with due regard to the longer 

 waves which may arrive from infrequent storms. The floating breakwater can 

 fail to meet its design objectives by transmitting a larger wave than can be 

 tolerated without necessarily suffering structural damage. Uncertainties in 

 the magnitude and types of applied loading on the system, and lack of mainte- 

 nance cost information, dictate conservative design practices which naturally 

 increase the initial project cost. A major disadvantage is that floating 

 breakwaters move in response to wave action and thus are more prone to 

 structural-fatigue problems. 



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