Construction: This FTB is 17.1 m (56.0 ft) in length and 6.4 m (21.0 ft) in 



width. Originally, the breakwater relied on trapped air for flotation and 

 on a variety of experimental materials, including rope, chain, and 

 stainless-steel cable, for coupling. This structure lasted approximately 

 2 years before the couplings failed and flotation became a major 

 problem. The reconstructed unit uses rubber conveyor belting fastened 

 with nylon bolts as the coupling material. Polyurethane foam poured into 

 the tire crowns now provides primary flotation. The only problem 

 encountered in constructing the breakwater was difficulty in drilling 

 through the belting. 



Site: 



POCASSET 

 HARBOR 



r^st 



12m 



Installation: The breakwater is anchored by five 909-kg (2,000 lb) concrete 

 blocks. Three of the anchors are positioned on the exposed side of the 

 structure and two on the leeward side. Mooring lines are of nylon/chain 

 and are 4.3 m (14.0 ft) in length. 



Field Experience 



Operation: Inadequate buoyancy and coupling failure posed major problems to 

 the original FTB. Since reconstruction, the breakwater has performed 

 admirably with no problems experienced. Under typical storm conditions 

 with waves 0.9 m (3.0 ft) in height and 8.9 m (29.2 ft) in estimated 

 length, the transmission coefficient is 0.17. 



Maintenance: Scheduled maintenance consists of inspecting the couplings and 

 moorings. 



Severe Storm Effects: During an unusually severe winter storm in 1976, winds 

 from the southwest reached 154 km/hr (83 kn) . Seas were 1.8 m (6.0 ft) 

 high. The operator noted that the breakwater was highly effective in 

 suppressing the swells and prevented any damage from being done to his 

 docks. He estimated that from $6,000 to $7,000 in potential damage was 

 averted by the FTB. 



Cost: The original construction cost in 1976 was $1,000. Reconstruction 



cost in 1980 was $2,000; this cost does not include the reused moorings. 



34 



