To produce a foam slug, regular automotive cup grease was applied to the 

 interior of a foam mold, then a large size plastic leaf or garbage bag was 

 inserted into the mold. A measure of two-part polyurethane foam was mixed and 

 poured into the plastic bag liner. As the foam agents reacted, the expansion 

 uniformly filled the interior of the mold, generally resulting in a rounded 

 crown on top. To recover the plastic-covered foam slug, the wooden end 

 retainers were removed along with the vise clamps. The rolled sheet tube 

 immediately opened, permitting the foam slug to slip out. Hand sawing in a 

 mitre-box "type fixture removed the crowned end, leaving a regular square 

 cylindrical shape. 



The partially greased foamed slugs were pushed into the steel tubes using a 

 pusher rod with a flat plate welded to the end. Void space was kept to an 

 absolute minimum by measuring and cutting the last slug to the correct length. 



Steel end caps 1/4 inch thick were welded into place at the ends of the 

 steel tubes. A pipe plug located in the center of each end cap permitted 

 pressurization of the tube to inspect for weld leaks prior to final sealing. 

 Leaks can be located with a filling gauge pressure of approximately 10 lbs. 

 (see Figure 5) using an appropriate soap solution. Calculations indicate that 

 the tubes themselves cannot become negatively buoyant even though leaks should 

 eventually develop. 



Figure 6 shows the operation of tire cladding the steel tubes. The far end 

 of the tube is resting on a fixed block and the center is supported by the 

 cradle crane lifting cable. 



Breakwater Design, Fabrication and Installation 



Having been funded to field test a state-of-the-art floating breakwater, 

 the pipe-tire design with its superior wave attenuation characteristics was 

 selected. This approach also accommodated the author's desire to field test two 

 newly conceived pipe-tire configurations. The matter was resolved by 

 constructing a system incorporating subassemblies of three different designs. 

 Comparisons of relative performance could then be obtained by placing the 

 measuring instruments in appropriate locations aft and near the various 

 assemblies. 



The design variations are limited to the manner in which the tire mazes 

 between neighboring tire-clad tubes is configured and attached. Figure 7 

 illustrates how the tires are positioned on stringers spanning the intervening 

 space and attaching to selected tires on neighboring pairs of tire cladded 

 tubes. This tire maze configuration is the V. Harms PT-1 design. It orients 

 the tire treads in the principal direction of wave advance (see Figure 8). 

 Loose coupling of the tires to the spanning stringers is a characteristic of 

 this design. Consequently, more careful foaming of the tires is required, as 

 each tire must be positively buoyant else it can sink beneath the surface while 

 still on the stringer. 



Figure 9 shows details of the truck tire maze stringers for the PGYM-1 

 design. Each stringer is of Goodyear modular design. This configuration 

 positions the tire openings in the principal direction of wave advance (see 

 Figure 10). It features a tightened bundling of the tires with neighboring 

 tires providing some positive lift in the event a tire is insufficiently 



46 



