some confusion with the term and links this area with inadequate buoyancy and 

 coupling failure. 



g. Instability (0.5/0.9) . Because of the habit of an FTB to collect 

 fouling growth, sand, silt, and litter on and in the tires, a once-stable 

 structure can quickly become unstable. This is exhibited when it starts to 

 sink at one of the far ends or at its exposed side. In extreme cases, this 

 bending over will increasingly release trapped air or foam in the positively 

 buoyant section until the entire structure suddenly sinks. Instability in an 

 FTB is certainly a function of inadequate buoyancy and poor maintenance. Par- 

 tial submergence is usually a solid indicator that total sinking may soon 

 occur. Since stability is linked with the quality of the flotation system, 

 those units which rely solely on trapped air for buoyancy have consistently 

 experienced the most severe problems. 



h..„ Mooring-Line Failure (0.5/0.6) . In every case where mooring-line failure 

 was cited, the anchoring system had also failed. Fortunately, mooring-line 

 failure is rare with anchors dragging much more often than lines breaking. 

 Typically, belting or chain is looped through several tires and joined at a 

 shackle to which the mooring pennant is connected. Evidently, whether by the 

 builders' intuitive knowledge or by a reversal in the design literature from 

 its previous stance on anchoring systems, overdesign is typical and mooring 

 lines manage to hold through the worst conditions. This last statement assumes, 

 of course, that the entire system has not been drastically dragged out of its 

 proper mooring configuration. In addition, if not properly maintained, any 

 mooring system will eventually fail due to fatigue and wear, but it appears 

 that no respondents have had their FTBs in location long enough for this prob- 

 lem to have arisen. Consequently, annual inspection is still advised, with 

 the replacement of lines showing weakness. 



i. Interference with Boating Traffic (0.5/0.5) . Frequently, an operator 

 noted that the FTB was a minor nuisance to boaters motoring through the area. 

 In no case was this category cited as a moderate, major, or extreme problem. 

 Several operators actually indicated that their FTBs served effectively in 

 controlling traffic near their facilities and, by doing such double duty, had 

 a clearly positive effect. 



j. Ice Damage (0.2/0.6) . Surprisingly, while several sites have flowing 

 ice present in the winter, ice damage to the FTB was never reported as more 

 than a minor problem. Flowing ice can build up tremendous forces on a moored 

 coastal structure and carry it along in its flow. Nonetheless, no notable 

 mooring or anchoring failures in this mode were cited. It is apparent, how- 

 ever, that several operators wisely sidestepped this problem by moving their 

 FTB in the winter to a less exposed site (e.g., lashed against a fixed break- 

 water or permanent dock) . Finally, one operator who has a rigid pier and dock 

 built atop his FTB noted that ice did cause moderate damage to the docks, 

 though had no effect on the FTB proper. 



k. Corrosion (0.2/0.1) . To a large extent, this category is subsumed under 

 coupling failure. Corrosion is indeed a severe problem for structures in salt- 

 water employing steel components and will usually lead to failure in 2 to 5 

 years unless excessively heavy steel couplers are used. 



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