material, anchoring system, and tieline used. Flotation and tieline 

 typically account for one-third of the breakwater cost. Labor and the 

 anchoring system account for most of the remaining costs as the tires can 

 usually be obtained free or at a nominal price. Typical costs reported 

 in 1977 (Candle and Fischer, 1977) for a four- module-wide breakwater (see 

 Fig. 5) varied from $15 to $40 per linear foot of breakwater with variable 

 labor costs accounting for most of variation in total cost, 



III. EXPERIMENTAL SETUP AND PROCEDURE 



1. Test Facility and Instriomentation . 



The FTB tests were conducted at prototype scale in CERC's large wave 

 tank which is 6.1 meters (20 feet) deep, 4.6 meters (15 feet) wide, and 

 194 meters (635 feet) long (Fig. 6) . Waves of constant period and height 

 were generated by a piston-type wavemaker. A 1 on 15 sand absorber beach 

 occupied 94 meters (308 feet) of the tank length during, the testing. A 

 schematic diagram of the large wave tank test setup is shown in Figure 7. 



Two Marsh McBimey model 100 water level gages were used to measure 

 the incident and transmitted wave heights. The output signals from the 

 gages were recorded on two channels of a six-channel Brush recorder. 

 The gages were calibrated for 2 meters full scale per channel. Mooring 

 loads were measured using a commercial load cell rated at 2,500 poimds 

 (1,135 kilograms). Before testing the FTB the load cell was checked by 

 applying known weights to the cell and recording the output signal from 

 the load cell. 



2. Module Arrangement and Test Setup . 



Two floating tire breakwaters--one containing 8 Goodyear modules, the 

 other containing 12--were tested. The modules were constructed as de- 

 scribed in Section II, using standard 14- and 15-inch automobile tires 

 and arranged to form test breakwater sections as shown in Figure 6. The 

 breakwater test sections were two modules long across the tank (parallel 

 to the wave crest) and four (Fig. 6, a) and six (Fig. 6,b) modules wide 

 along the tank (in the direction of wave travel) . Since the test section 

 was only two units long, various modifications were made to the test 

 section to make the performance of the breakwater resemble that of an 

 actual breakwater several hundred meters long. First, 1.9-centimeter- 

 diameter (0.75 inch) stabilizer bars were attached to the front and rear 

 modules and an open- link chain was secured along both sides of the break- 

 water to prevent the modules from being pulled together because of the 

 lack of adjacent restraining modules along each side. In addition, 

 wooden bun5)er plates were attached to the two outside tires of each 

 module (normally used for attaching other modules) to prevent the tires 

 from scraping the tank walls. A plan view of the modules and modifica- 

 tions is shown in Figure 8. 



The test structure was placed in the tank (Fig. 7) , with its seaward 

 edge at station 56.3 (from the wave generator). Incident wave heights 



16 



