X 



(c) Determine the W/L ratio for the required K^ 

 and compute the breakwater width. From Figure 3, where 



Ky. = 0.33, W/L = 1.38. Thus, the required breakwater width, 

 W = (W/L)(L) = (1.38) (37 feet) = 51 feet. 



(d) Determine the number of modules required which is 

 equal to W (module width) or 51 feet per 7.0 feet per 

 module =7.3 modules required. Thus, the breakwater would 

 have to be at least eight modules wide to obtain the desired 

 wave height reduction. 



(2) Determine the mooring load. Using Figure 4 and an incident 

 wave height equal to 3.0 feet, the design load is 77 pounds per lineal 

 foot of breakwater parallel to the wave crest between the anchor lines. 



Assuming an anchor spacing of 50 feet, the total mooring-line load 

 per anchor is : 



F t = 77 lb/ ft x 50 ft = 3,850 lb . 



NOTE. --The mooring-line load from Figure 4 is used as the lateral 

 mooring-line load because they are essentially equal for the 1 on 7 

 slope specified. 



(3) Design of a mass concrete anchor. Since the bottom is 

 assumed to be level firm sand, the coefficient of static friction, 

 u, is assumed to be 0.4. Also, the assumed unit weight of concrete 

 in air, w , is 150 pounds per cubic foot and the unit weight of 

 freshwater, Wy, is 62.4 pounds per cubic foot. Substituting the 

 equation (3) and solving for the total mass weight of the anchor, W^, 



W t 



Vs 



Thus, using F = 1.5 and F^Fg = 3,850 x 1.5 = 5,875 lb (or 6,000 lb) 



6,000 lb 



v (0.4) (1 - 0.416) 

 W, = 25,685 lb (12.8 tons) for each 50-foot section 



The volume is 



25,685 lb _ yj\.2 ft 3 (approximately 5-foot 7-inch cube) 

 150 lb/ft 3 



18 



