b. Inadequate Buoyancy (2.3/1.4) . The original Goodyear design advocated 

 a flotation system which relied on air trapped in the crowns of the tires and 

 was replenished by normal wave action. By 1975, URI researchers had deter- 

 mined that this system was inadequate for long-term continuous use in salt- 

 water; nonetheless, many of the structures surveyed, including some built in 

 the late seventies, relied on this method for buoyancy. Without exception, 

 this system failed for structures in saltwater and often failed for those in 

 freshwater. In saltwater, an FTB usually will be overcome by fouling growth 

 and however much air is trapped in the tire crowns will be inadequate to pre- 

 vent some, if not all, of the structure from sinking. In freshwater, the 

 system appears to work if compressed air is regularly blown into the struc- 

 ture to replace that which has escaped or been absorbed into the water. Often- 

 times, such a measure was not included in routine maintenance, particularly 

 for unattended sites. 



To overcome flotation problems, many operators attempted to insert poly- 

 ethylene blocks into the tire crowns. This procedure was usually a very dif- 

 ficult undertaking and a stopgap measure at best. Those blocks inserted in 

 tires on the outer modules came loose and floated away under moderate wave 

 action. Internal tires typically retained the foam under most sea conditions, 

 which did allow for a modest improvement in buoyancy. A more successful 

 approach was to pour liquid polyurethane foam into the tire crowns before 

 assembling the modules. This expanded foam formed a much tighter fit and pro- 

 vided much greater buoyancy. While the foam is brittle and can break, then 

 wash out under severe wave action, this method appears to be the most success- 

 ful of all methods, for both saltwater- and freshwater-based designs. The 

 greatest drawback with poured foam is its initial expense. 



c. Litter Entrapment (2.0/2.0) . Whether on saltwater or freshwater, an 

 FTB will trap floating debris and can become an esthetic annoyance. This 

 problem appears particularly acute in heavily traversed inner harbors and 

 sites which have unusually fast currents. The only known solution is a regu- 

 larly scheduled handpicking of the structure. Fortunately, litter entrapment 

 appears to have no functionally bad side effects as does, for example, fouling 

 growth. Two operators did not even regard litter entrapment as a problem. 



One was in the unique situation where a pier and set of docks were built atop 

 a portion of his FTB. This accessibility permitted easy cleaning; however, 

 the accessibility also meant that children would play on and around the struc- 

 ture which presented a safety hazard. The second operator expressly intended 

 his very long FTB to act as a debris gate and keep his marina clean. 



d. Anchoring System Failure (1.8/0.8) . In this case, the mean severity 

 rating is misleading. Anchoring system failure is usually catastrophic, with 

 either a major or extreme failure occurring or no failure happening at all. 

 The projects which did experience failure were, in hindsight, logical ones. 

 Two sites found hurricanes passing overhead, one was directly exposed to an 

 incredible fetch across the width of Lake Michigan and a fourth was positioned 

 at a point experiencing some of the strongest tidal currents in the United 

 States. In such cases, truly massive anchoring systems were required to hold 

 the structure in position; otherwise, a reconsideration of whether an FTB is 

 even appropriate for the site was in order. 



There appears to be no simple solution to anchoring system failure. Main- 

 taining any floating structure in place under severe sea conditions has always 



