c. Anchor Force Tests with Chain Mooring System . Davidson (1971) per- 

 formed tests at both water depths to determine the forces in the anchor chains 

 for each wave condition tested. Strain gages were mounted in such a way as to 

 measure the vertical and horizontal components of the force in each anchor 

 chain. The force components recorded at each anchor were then analyzed and 

 combined into the resulting force for that chain. For each chain, the peak 

 anchor force was taken as the sum of the initial force placed in the anchor 

 chain and the highest peak force that occurred for a given test condition. 

 The average anchor force was taken as the sum of the initial anchor chain 

 force and the average of the highest one-third of the peak anchor forces meas- 

 ured during a test. The chain anchor force data are shown in Figure 37 as 

 plots of the anchor force per foot of structure width versus incident wave 

 height. 



The chain anchor force test results show that, although there is some 

 scatter of the data points, definite trends are established from which the 

 peak or average of the one-third highest force can be selected. The anchor 

 force test results at both depths show, with the exception of the 2.0-second 

 wave period and a 29.5-foot depth, that the maximum peak anchor force is 

 greater on the seaside anchors than on the harborside anchors. Considering 

 the range of incident wave conditions at Oak Harbor, the maximum peak anchor 

 force on the seaside was found to be about 300 pounds per linear foot of 

 structure; the maximum peak anchor force on the harborside was about 220 

 pounds per linear foot of structure. 



d. Anchor Force Tests with Pile Mooring System . During the transmission 

 tests on the pile mooring system, the forces exerted on the restraining piles 

 in the direction of wave travel were measured for each wave condition, using 

 strain gages mounted flush with the floor on each of the piles. Thus, it was 

 assumed that, on the average, the forces applied by the module to the piles 

 during testing would be in the plane of the Stillwater level. At the time of 

 testing, the exact type of prototype pile to be used and its energy absorption 

 characteristics had not been determined. Hence, it was assumed that with 

 known forces on a pile with no deflection and absorption, it would be possible 

 to determine with sufficient accuracy the forces on selected prototype piles 

 with given deflection and absorption characteristics. 



The pile mooring force test results are presented in Figure 38 as plots of 

 the force on a pile per foot of structure width versus incident wave height. 

 In each of the pile force plots, the solid line represents the maximum summa- 

 tion of forces per foot of structure width that simultaneously occurred on the 

 model piles. The dashlines represent the limits of the range of forces that 

 expected to occur on a pile due to the relative positions of the breakwater 

 module and the pile. There is sufficient trend in the data to approximate the 

 extreme forces exerted on a pile by the breakwater module under the given wave 

 conditions. The maximum force on the seaside of the pile was found to be 

 about 4,200 pounds per linear foot of structure width (2.5-second curve); the 

 maximum force on the harborside of the pile was about 4,600 pounds per linear 

 foot of structure width. Before the pile mooring data from these tests are 

 used for prototype design, the type of model mooring system used to obtain the 

 pile force data should be noted and the resulting data adjusted in accordance 

 with the deflection and absorption characteristics of the selected prototype 

 piles. 



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