Total 

 Resultant 



Mooring 

 Force 



12 3 4 5 6 7 



Windslpeed [Beaufort Scale) 



Effect of windspeed on mooring force 



b. 



Tide Stream Rate [ knots] 



Effect of tidal current on mooring force 



Figure 185. Effects of windspeed and tidal current on Harris floating 

 breakwater at Stokes Bay (after Harris and Thomas, 1974). 



3. Parabolic Beaches. 



The floating, parabolic beach breakwaters (hinged or free floating) are 

 essentially special floating sloping barriers. They differ, however, from the 

 sloping-float breakwater in that the design attempts to cause wave damping by 

 forced instability and breaking of the incident waves, producing a counter 

 current by the motion of the breakwater, and by absorption of energy through 

 the deflection of the structure. Ofuya (1968) evaluated parabolic beaches 

 with structures made of wooden beams of the form: 



y 2 =4^ 



y 3d 



(81) 



where y is the vertical distance from sea bottom, x the horizontal dis- 

 tance from hinged or anchored end, and d the water depth at the site. 

 Schematics of the structures with wooden slats of equal sizes placed over the 

 beams are shown in Figure 186. Restraint was provided by pivotal points at 

 the bottom of the experimental wave channel for the hinged beach, and the 



245 



