Site: 



LAKE N 



MICHIGAN 



T 



Installation: The breakwater was anchored by twenty 1,226-kg (2,700 lb) 



concrete blocks. On the structure's exposed side, the anchors were spaced 

 7.6 m (25.0 ft) apart and on its leeward side, 15.2 m (50.0 ft) apart. 

 Mooring lines were of chain and were 10.4 m (34.0 ft) in length. 



Special Equipment: Two navigational lights were installed at each end of the 

 structure and a daymarker was placed in the center. 



Field Experience 



Operation: Inadequate buoyancy and sand accumulation in the tire bases were 

 extreme problems resulting in the partial submergence of the structure 

 within a few months of its installation. The operator noted that the 

 polystyrene was damaged by gasoline on the water and believed that the 

 polyurethane foam absorbed water. Anchoring system failure (see Severe 

 Storm Effects) and instability were both regarded as major problems. 

 Structural failure was cited as a moderate problem and mooring- line 

 failure was considered a minor problem. During moderate wind conditions 

 with waves 0.9 m (3.0 ft) in height and 18.5 m (60.7 ft) in estimated 

 length, the transmission coefficient was 0.67. Under worst lake 

 conditions, the FTB was considerably less effective with the operator 

 noting that a much wider tire mat was needed. 



Maintenance: No scheduled maintenance was conducted during the brief 

 deployment of the FTB. 



Severe Storm Effects: During the first major storm encountered, the FTB was 



dragged from its position, indicating a totally inadequate mooring system. 

 The breakwater was also ineffective in significantly reducing the height 

 of the swells. Inasmuch as these conditions were the design conditions 

 and the FTB exhibited no effectiveness, the structure was permanently 

 removed. 



Cost: The construction materials cost $30,000; labor cost was $60,000. 



Planning and engineering fees were an additional $1,000. These figures 

 translate to an overall cost of $141.96/m 2 ($13.19/ft 2 ) in 1980 dollars. 



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