No harborside anchor forces were detectable during any of the chain 

 anchor tests with a 10-foot depth. The seaside and harborside chain 

 anchor forces for tests with a water depth of 29.5 feet are shown in 

 Figures 6-58 and 6-59. The results of the pile mooring force tests are 

 shown in Figures 6-60 through 6-63. The type of model mooring system 

 used to obtain the pile force data should be noted, and the model data 

 should be adjusted by the deflection and absorption characteristics of 

 the selected prototype piles before pile mooring data are used for proto- 

 type design. 



(6) Pneumatic Breakwaters . 



(a) Project . Application of pneumatic breakwaters to 

 Transportation Corps, Department of the Army, problems of offshore 

 discharge. 



(b) Reference . Sherk (1960). 



(c) Laboratory . CERC. 



(d) Test Period . August to September 1959. 



(e) Problem . The development of a new series of amphibians 

 required an examination of the problems involved in the transfer of cargo 

 from conventional ships to amphibians in offshore discharge operations. 

 The main problem is that amphibians used for offshore discharge are se- 

 verely curtailed when wave heights exceed 2 feet; the degree of curtail- 

 ment increases with wave height with nearly 100-percent loss of discharge 

 capability when wave heights exceed 8 feet. If relatively calm water 

 could be produced around ships at anchor and if a relatively calm track 

 of water could be produced through the surf zone, the capability of mov- 

 ing supplies ashore would be increased considerably and moderate sea con- 

 ditions would not reduce over-the-beach supply to a mere trickle. 



(f) Purpose of Study . The investigation was conducted pri- 

 marily to determine the practicability of using pneumatic breakwaters 

 (i.e., a screen of rising air bubbles) to reduce wave heights sufficiently 

 to allow offshore discharge operations during moderate wave conditions. 

 Because of scale effects, with respect to the quantity of air required 

 for adequate wave height reduction, full-scale tests were necessary to 

 obtain more conclusive evidence of the feasibility of using the pneu- 

 matic breakwater for the protection of offshore discharge operations. 



(g) Test Facilities . After investigation of several wave 

 flumes, the Transportation Corps selected the large wave-flume facility 

 available at CERC (then called the Beach Erosion Board) at its Washington, 

 D.C. location. This was the only wave flume where tests could be con- 

 ducted for conditions approaching full scale. The concrete flume is 635 

 feet long, 20 feet deep, and 15 feet wide. The wave generator was a 

 piston-type powered by a 510-horsepower, constant-speed motor capable of 

 generating waves with periods from 2.6 to 16.0 seconds and wave heights 



429 



