was provided by the Floating Breakwater Prototype Test Working Group comprised 

 of representatives from OCE, the US Army Engineer Waterways Experiment Station 

 (WES), the Coastal Engineering Research Center (CERC) (now at WES), the Seattle 

 District (NFS), and the North Pacific Division (NPD). The Seattle District 

 had primary responsibility for carrying out all major facets of the program 

 except data analysis, which is the responsibility of CERC. 



The breakwater test site was in Puget Sound off West Point at Seattle, 

 Washington (Figure 1). The site was in an exposed location, assuring that, 

 within the period available for testing, wave conditions would approximate de- 

 sign waves normally associated with sites currently considered suitable for 

 floating breakwaters. Water depth at the site varied between 40 and 50 ft at 

 mean lower low water (MLLW), and bottom materials consisted of gravel and 

 sand. The diurnal tide range at the site was 11.3 ft, and the extreme range 

 was 19.4 ft. 



The prototype structures that were built and monitored were of two types: 

 a concrete box design (Figure 2) and a pipe-tire mat design (Figure 3). The 

 concrete breakwater was composed of two 75-ft-long units, each 16 ft wide and 

 5 ft deep (draft of 3.5 ft). The pipe-tire breakwater was composed of nine 

 16-in. -diameter steel pipes and 1,650 truck tires fastened together with con- 

 veyor belting to form a structure that was 45 ft wide and 100 ft long. 



DESIGN AND CONSTRUCTION 



The concrete structure design was based on field and design experience 

 from numerous floating structures now in use, available model test data, and 

 detailed structural analysis of similar structures (Adee, et al., 1976; 

 Carver, 1979; Davidson, 1971; and Hales, 1981). The pipe-tire mat breakwater 

 was based on a sea grant-funded design by Professor Volker Harms (Harms and 

 Westerink, 1980) and modified based on local site conditions and personal dis- 

 cussion with Professor Harms. Other types of floating breakwaters, such as 

 log bundles and twin pontoons, or A-frames, were considered; but either high 

 construction costs, lack of broad applicability, or overall test program bud- 

 get limited testing to the box-type concrete float and the pipe-tire mat 

 structures. Based on available design information, the breakwaters were sized 

 to provide acceptable wave attenuation under conditions typical of sites where 

 the future use of floating breakwaters is anticipated (i.e., H = 2 to 4 ft, 



110 



