However, the new design with larger chain and cathodic protection is expected 

 to last a long time. 



The connections between modules have been the "Acnille's Heel" in floating 

 breakwater design. Experience has had to substitute for analysis in evalua- 

 ting the loadings to be transferred between modules. The recent dynamic 

 structural response modules are expected to provide realistic design values, 

 thereby replacing the costly empirical experience approach. Some design pro- 

 gressions show up in the installations covered in this report. The rubber in 

 the chain-bumper system of the initial Tenakee design took a permanent set and 

 allowed slack to develop. Tlie replacement design eliminated the set problem 

 by connecting the flexible rubber fender rigidly to each module. The connec- 

 tions of the breakwater deck to the flotation modules in the Friday Harbor 

 breakwater invited stress reversals and concentrations with subsequent fatigue 

 failures. The layout of the connections for the Semiahraoo Marina looked like 

 a practical way of providing a resilient, flexible connection well suited to 

 field assembly. Its performance, however, suggests it was underdesigned for 

 the loading imposed by the high winds experienced in the 1981-82 winter. The 

 current design trend for the caisson-type breakwater is to replace the flex- 

 ible connection by posttensioning modules to form a continuous structure. 

 Although more expensive, fabrication and field assembly procedures are more 

 exacting; therefore, the final product should be cost-effective. 



Design data for the pile-restrained breakwater have a rather weak base. 

 Logical assumptions about wave loadings on such piling can lead to forces 

 that do not appear to develop in the field. Dynamic analysis will require the 

 resolution of the interaction between the piling and the breakwater; such a 

 synthesis would be aided greatly by some prototype data. The floating break- 

 water at Camas -Washougal would be a possible site for field experiments, as 

 would the unit at Everett Harbor. An energy absorbing connection between the 

 pile collar and the breakwater would relieve some of the dynamic load. A sug- 

 gested design would be concentric annular rings, with the annulus taken up by 

 rubber fendering material. 



The pros and cons of lightweight versus regular weight concrete may have 

 been resolved by market conditions. Suitable lightweight aggregate has become 

 very expensive. 



Some standardization of breakwater dimensions could lead to lower design 

 and fabrication costs. 



Those breakwaters where the freeboard is more than 1 foot should have 

 safety ladders provided at intervals of about 150 feet to allow a person to 

 climb onto the breakwater unassisted. 



Navigation or radar targets should be placed at more frequent intervals 

 than those required by U.S. Coast Guard regulations. The floating breakwater 

 is difficult to see under dark, stormy conditions. 



Some designers strongly prefer chain or chain-nylon line anchor lines over 

 cable, which is likely to be more vulnerable to corrosion. 



Quality control in fabrication is very important to ensure adequate cover- 

 age of reinforcement and strict adherence to dimensions so the units will 

 float with uniform and specified freeboard. 



63 



