been a monumental task and, at a certain point, all systems will fail. A 

 builder must be aware of site conditions and determine the risk he or she is 

 willing to take. Unfortunately, many operators indicated that the loads 

 experienced by their FTBs were much greater than that postulated in the early 

 technical literature. Consequently, there may be a serious gap in the theo- 

 retical knowledge of these systems, if not in the problem of access to more 

 recent, definitive studies. 



e. Coupling Failure (1.0/0.8) . Many materials are used to couple the 

 tires together. Rope was the first to be tried in the original 1974 trials, 

 where it was found to quickly chafe, untie, and fail. (One early FTB was 

 invaded by a colony of snapping turtles which quickly ate through almost every 

 rope holding the structure together.) Wire and cable are used, though these 

 materials can easily cut through the tires and corrode in saltwater or acidic 

 freshwater. Nylon strapping has been tried, only to find that it will chafe 

 and fray until failure occurs. Chain is frequently employed, but it is a 

 very heavy coupler, will also corrode, and can abrade the tires. In contrast 

 with the above couplers, rubber conveyor belting has been used with notable 

 success. One FTB, under the influence of Hurricane Frederic in 1979, was 

 ripped from its mooring site and dashed against a rock groin; yet, the tire 

 mat coupled by conveyor belting remained intact. (The combined holding power 

 of the anchoring system which dragged was estimated to be 235,700 N (53,000 

 lb).) Working with the belting can be as simple as with any other coupling 

 material. The belting is easily cut by a sharp knife blade or handsaw and 

 cold-punching bolt or rivet holes is straightforward. Drilling through the 

 belting is not advised for the generated heat will cause the rubber to melt 

 and subsequently bind the bit. 



Fasteners for the coupling materials include clamps, bands, rivets, and 

 bolts. To avoid the corrosive tendencies of saltwater, nylon bolts, dyed 

 black to prevent ultraviolet deterioration, have met with good success. (If 

 the nylon bolts are tightened too much, high internal stresses will result and 

 the bolt may shear when strained.) While bolts can pull through the flexible 

 hole in the conveyor belting or shear in tension, if properly fastened, nylon 

 bolts have a very low failure rate. (One operator reported a 3- to 4-percent 

 failure rate over 2 years of operation including the passing of two hurricanes.) 

 At most freshwater sites, galvanized-steel bolts are sufficient with stainless- 

 steel or nylon components being needlessly expensive. One enterprising builder 

 on freshwater employed 6061-T6 aluminum rivets and, after 2.5 years of expe- 

 rience, now advocates their use. Davis (1977) l is the most definitive study on 

 coupling materials. 



f. Structural Failure (1.0/0.8 . The purpose in examining this category 

 was to learn of any structural faults in the primary construction material 

 used in the FB. In the case of a Goodyear design, the primary construction 

 material is the scrap automobile tire. With the exception of a few tires 

 sawed through by wire, cable, or chain, the surveys indicate that the tires 

 withstood all the punishment anticipated in an ocean environment. The rela- 

 tively high rating given this category by the respondents probably indicates 



^AVIS, A. P., Jr., "Evaluation of Tying Materials for Floating Tire Break- 

 waters," Marine Technical Report No. 54, University of Rhode Island, 

 Kingston, R.I., 1977. 



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