pile mooring system in the model consisted of a pile on each end of the 

 module, with each pile fitted with a strain gage at the bottom of the 

 flume and calibrated to measure the seaside and harborside forces in 

 the direction of wave travel (Fig. 6-53). 



(h) Test Procedures . The unrestrained natural period of 

 oscillation of the breakwater was determined by applying a torque to the 

 structure in still water and measuring (by a stopwatch) the time required 

 for the module to oscillate from one extreme position to the other extreme 

 and back to the first position. An attempt to determine the period of os- 

 cillation of the module while it was restrained by the chain-mooring system 

 was not successful because the module would not oscillate in the restrained 

 condition sufficiently to allow determination of a complete period of os- 

 cillation. The effectiveness of the proposed floating breakwater in atten- 

 uating wave action was determined by measuring the heights of incident and 

 transmitted waves. The incident waves were measured at the position of the 

 module before it was placed in the wave flume. The transmitted waves were 

 measured during a test with the module placed in the restrained conditions, 

 at distances of 1 and 1.5 wavelengths shoreward of the structure. Wave 

 heights were measured by printed-circuit gages and a CEC oscillograph; 

 photos were also made of several wave conditions (Fig. 6-54). Mooring 

 forces were measured for most waves used in the transmission tests. Chain 

 anchor-force data were obtained from the strain-gage measuring blocks 

 mounted on each anchor chain; pile anchor-force data were obtained by 

 strain-gaged piles in conjunction with the amplifier-oscillograph assem- 

 bly. Observations were made during all the tests to determine whether 

 the module and mooring system were in resonance with any of the wave con- 

 ditions tested. Stillwater levels for this type of model study are se- 

 lected so that the effectiveness of the proposed floating structures can 

 be obtained over the range of depths corresponding to the local tide con- 

 ditions. The tide elevations at Oak Harbor range from an estimated maxi- 

 mum of +14.5 to -4.5 feet MLLW (MHHW is + 11.4 feet MLLW) . Since most of 

 the proposed breakwater length would be located in depths from 10 to 15 

 feet MLLW, depths of 10 feet and 29.4 feet (corresponding to tide eleva- 

 tions of 0.0 and +14.5 feet MLLW and bottom elevations of -10 and -15 feet 

 MLLW, respectively) were selected for low tide and high tide conditions, 

 respectively. Hindcast data for the Oak Harbor vicinity indicated that 

 the maximum incident wave conditions would be a period of about 3.5 sec- 

 onds and a height of about 2.0 feet. Model tests used v;ave periods from 

 2.0 to 3.5 seconds and wave heights to 5.0 feet. Wave heights larger 

 than 2.0 feet were tested so that the effectiveness of the proposed 

 structure (as determined in the Oak Harbor model study) could be used 

 in determining the feasibility of using similar floating structures at 

 locations with more severe wave conditions. 



(i) Summary of Test Results . The natural period of the 

 proposed breakwater unrestrained was 7.1 seconds (prototype). The wave 

 transmission data (Figs. 6-55 and 6-56) show that the proposed breakwater, 

 either a chain or pile mooring, will adequately attenuate waves as large 

 as 2.0 feet in height with a period of 2.5 seconds. The seaside chain 

 anchor forces for the 10-foot depth conditions are shown in Figure 6-57. 



423 



