severe wave conditions than those normally considered acceptable for floating 

 tire breakwaters. For this reason, the PT-1 module was emphasized in the test 

 program. Although structural failures were not experienced on either the PT-1 

 or the PT-2 breakwaters throughout the many weeks of testing, and posttest 

 inspections did not reveal areas of imminent failure or excessive wear, it 

 became clear that the PT-2 module was inherently more pliable than the PT-1 

 module because it was composed of automobile tires, not truck tires. Conse- 

 quently, as waves broke over the structure, greater compression and displace- 

 ment of leading-edge tires occurred on the PT-2 module than was true for the 

 PT-1 module under the same conditions. Although PT-Breakwaters were designed 

 to be pliable, with relative motion between individual components, under 

 severe wave-induced loads, the observed compression of leading-edge tires 

 on the PT-2 module is felt to be excessive for continuous operation. It is 

 therefore suggested that the PT-2 breakwater be limited to sites with signifi- 

 cant wave heights of less than 0.9 meter; this condition is considered to be 

 equally appropriate for Goodyear or Wave-Maze floating tire breakwaters that 

 are composed of automobile tires as well. The value of 0.9 meter was chosen 

 by the researchers as representing the best, though inherently somewhat sub- 

 jective, estimate for the maximum acceptable significant wave height; it is 

 based on extensive laboratory observations and experience with a variety 

 of field installations. The above rule is considered to be of practical 

 importance because it reminds the designer that the environment is hostile 

 and that PT-Breakwaters constructed from automobile tires are inherently less 

 rugged than those composed of truck tires; both have survival limitations. 



The wave attenuation performance of PT-Breakwaters improves as either 

 wavelength or water depth decreases, or the wave steepness increases (i.e., 

 C t increases with L/B and decreases with D/d or H/L) . The shelter 

 afforded by a particular PT-Breakwater is strongly dependent on the incident 

 wavelength: substantial protection is provided from waves that are shorter 

 than the width of the breakwater (i.e, L < B) , but very little from waves 

 longer than three B. As the water depth decreases, the wave attenuation 

 performance improves; a breakwater that provides inadequate shelter at high 

 tide may therefore be satisfactory at low tide. Wave attenuation generally 

 improves with increasing wave steepness, especially for relatively long waves 

 in shallow water (e.g., L > 3B and d < 3D). This behavior is attributed 

 principally to the inherent instability of waves, which increases with wave 

 steepness and, for waves near the breaking limit, is so great that only a 

 small perturbation is required to "trigger" the breaking process. For steep 

 waves, breaking was observed to start just seaward of the breakwater with 

 large amounts of energy being dissipated as the wave rolled and surged over 

 the breakwater. The wave attenuation performance of the PT-1 module was found 

 to be superior to that of the PT-2 module and the Goodyear breakwater. For 

 L/B = 1 (and deep water with d > 3D and H/L = 0.04), for example, the wave 

 height transmission ratio was approximately C t = 0.6, 0.4 and 0.2 for the 

 Goodyear, PT-2, and PT-1 breakwaters, respectively. Wave transmission curves 

 given in this report should not be used to design breakwaters that are less 

 than 9 meters wide or more than 15 meters wide (see Harms, Bishop, and 

 Westerink, 1981 for further data). 



For a given breakwater, the peak mooring force, F (on the seaward moor- 

 ing line, per unit length of breakwater) was found to depend primarily on the 

 wave height, H, and water depth, d, with wavelength, L, apparently only 

 of secondary importance. For the conditions investigated, F increases 



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