reasons for this change. Fiberglass shells are still the most common of the thin shell types, 

 but foam fillers are often provided. Tubular metal floats for freshwater use are now nearly 

 all foam-filled. They are particularly serviceable in areas where ice formation and heavy 

 floating debris are problems. Monolithic concrete shell-and-deck units are now almost 

 universally cast around foam cores. Nearly all the metal box floats (Fig. 75) are also 

 foam -filled. 



Figure 75. Metal box floating pier system. Note collection of surface debris due to 

 continuity of flotation elements, with no gaps for debris to flow through. 



One type of floating construction tliat appears ver) promising is the fiberglass or 

 plastic-coated shell with a molded foam core over wliich a reinforced concrete deck is 

 poured (Fig. 76). The edge beam and the crossbeam and tie rod system in this construction 

 make the units exceptionally strong, if the concrete is properly mixed and placed. Although 

 topheavy, there is no danger for a hcadwalk with finger piers of this construction to turn 

 over. The extra weight and stiffness of the concrete deck add an element of inertia under 

 pedestrian traffic that makes it approximately equal to t'nc monohthic concrete 

 shell-and-deck float in stability. However, the extra weiglit of concrete or part-concrete 

 floating units places a severe stress on the unit connecting stringers and on the finger 

 headwalk connections under moderate wave or surge conditions. For this reason, heav}' 

 floating systems should be installed only in well protected basins. 



126 



