(c) Tensile Strength: 40 pounds per square inch minimum at break. 



(d) Shear Strength: 25 pounds per square inch minimum at break. 



(8) Moisture Absorption: The maximum water absorption shall be 0.12 

 pounds per square foot of skinless or rindless surface when tested by immersion 

 method in accordance with U.S. Department of Defense, Mihtary Specifications 

 Mil-P-40619 (3 April 1962) 4.5.7. 



(9) Hydrocarbon Resistance: Polystyrene planks to be used in the vicinity 

 of gas docks or other areas subject to petroleum products floating on water shall 

 be hydrocarbon resistant. The materials shall show no apparent softening or 

 swelling when tested by the immersion method specified in the U.S. Department 

 of Defense, Mihtary Specifications MIL-P-40619 (3 April 1962) 4.5.10. 



(10) Shape: Surfaces of the finished planks shall lie in normal planes so that 

 the plank, when installed in final position in the floating dock, shall lie in a true 

 horizontal plane with the water. Edges formed by molding or cut sections may be 

 either rounded or square." 



Polyurethanc foam is more costly than polystyrene foam, but is sometimes preferred 

 because it can easily be "foamed" into a mold without expensive processing. Also, it is 

 naturally hydrocarbon-resistant. Two types are available, but only one is nonabsorbent— the 

 monocellular variety, which should always be specified. Like polystyrene, it should have 

 protective covering for marina use. 



Care must be used in selecting coatings to ensure compatibility with the base foam. 

 Polyester resins cannot be used with polystyrene, but will bond well with polyurethanc. 

 Polyvinyl-acetate emulsion and dense polyurethanc may be applied directly to polystyrene 

 foam which makes a fairly tough coating. Epoxy glues should be used to bond separate 

 boards of polystyrene foam; epoxy -bonded protective coatings may be used with either 

 foam. If the additional protection of a fiberglass and resin application is desired over 

 polystyrene, an epoxy coating compatible with the resin must be first appHed. Where wrap is 

 used, it should be lapped well over the top shoulder of the foam and not carried to the top 

 edge, as the wrap may peel away from the foam (Fig. 74). 



The two most common methods used to secure foam floats to deck structure are: (a) 

 hardware dowels driven on a skew into the foam through holes in the bearing boards, and 

 (b) 2-inch nylon strapping. The strapping method is preferred because it is more secure and 

 easily removed if the float has to be replaced or repaired. Bearing boards must have enough 

 bearing surface to prevent crushing the foam under maximum loading. The foam can be 

 loaded to about 5 pounds per square inch; however, it is weak in bending strength, and 

 bearing contact areas should be spaced not more than 2 feet apart, and continuous along 

 each edge. 



Most of the hollow shell floats are now being replaced with foam -filled shells. Few 

 shell-type floats are being manufactured without a foam core of some kind. Problems with 

 leakage, internal condensation of moisture, and vandalism (mainly bullet punctures) are the 



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