can be held at a constant elevation above the bottom, with a minimum of 

 wave-induced motion. 



A screed box is hung by cables from a traveling bridge mounted on 

 the deck of the screed barge. These cables are adjustable so that the 

 underside of the box can be lowered to a predetermined elevation. Once 

 the screed is lowered to the desired elevation below the barge deck, 

 screeding is ready to proceed. 



A stone-placing barge, with crane on deck, is then brought alongside 

 the screed barge. An aggregate-supply barge is positioned and tied 

 outboard of the crane barge. Aggregate is placed in the hopper mounted 

 on the traveling bridge and fed into the screed box through telescopic 

 trunk pipes which hang from the traveling bridge. As the screed box is 

 pulled forward, the crushed stone bedding is deposited in a layer on the 

 bottom. The top of the layer is struck off evenly by the bottom edge 

 of the trailing side of the screed box. The screed box is slowly pulled 

 forward until the run is completed. 



The screed box is then partially raised, and the screed barge 

 refloated; the counterweights are raised slightly and the screed barge 

 moved laterally to the next position. When the barge is in position, 

 the counterweights are reset, the barge hull submerged and the screed 

 box lowered. The barge is then ready for the next screeding run. When 

 sufficient stone bed has been placed and screeded, the screed barge casts 

 off its anchor lines and is removed from the site so that the next con- 

 crete breakwater unit can be brought in and set. The cycle is repeated 

 as necessary. 



d. Setting Concrete Breakwater Units . Each precast unit is towed 

 from the outfitting area by two tugs. As the unit approaches the break- 

 water site, the tugs move to each side of the unit and slowly pull it 

 close to the setting location. Hauling lines are secured between the 

 floating unit and the leading end of the previously set inplace unit. 

 Winches mounted on the inplace unit slowly draw the floating unit into 

 position and then is partially flooded. The tugs hold the floating unit 

 in line against wind, waves and current. This sequence of operations 

 is illustrated in Figure 21. 



The unit, when pulled closer to a final setting position, has been 

 flooded enough so that the bottom is within inches of the screeded stone 

 bed. A final check is made on alinement of the floating unit and, by 

 adding additional ballast, is founded on the stone bed. Full ballast 

 is then added for stability. 



Settlement of the units should be less than 2 inches because of the 

 designed low bottom pressure. 



The winches are removed from the preceding unit and reset on the 

 newly founded unit. All towing bitts, cleats and towing lines are 

 removed and returned to the finishing site to be mounted on another 

 breakwater unit. 



39 



