Entire Document - California Department of Boating and Waterways ...

......................................................................C6.6 Pontoon SpecificationsCommentary:Some older pontoon shells that are still in service were made of roto-castpolyethylene. Made two at a time, they came out of the molds much like two breadpans connected at their rims. They were cut apart, resulting in two open-toprectangular hollow pontoon shells. Such shells were filled with pre-expanded foamsnugly inserted into the shells, and capped with pressure treated plywood. 10 millpolyethylene sheeting was placed over the open-top foam-filled pontoon before theplywood cap was put on. This procedure helped stiffen the pontoon flanges,strengthened the connection to the dock frame, and helped ensure a watertight sealalong the lip of the pontoon.When this type of polyethylene pontoons are attached to the bottom of the frame,typically with galvanized lag screws and washers on 4 to 6 inch centers, a 2"x2"pressure treated wood backing strip should be used to insure that the pontoonflanges and covers are secured perfectly flat against the dock frame. This will guardagainst puckering of the pontoon flanges that tends to occur during warm weatheras the result of thermal expansion. Such puckering forms small “mouths” betweenthe lag screws that literally drink water in the splash zone around a pontoon andallow it to enter into the pontoon, filling existing air gaps, and progressively alteringthe buoyant characteristics. For example, where wind chop occurs primarily on thewarm sunny side of an existing dock, pontoons will “sip” water on that side only, andthe growing internal hydraulic pressure will gradually push the pontoon walls awayfrom the foam cores. This can result in severe listing of the pontoons, a situationthat is not usually self-righting.Roto-cast polyethylene pontoons presently being used on marina docks are moldedas self-contained units that are completely enclosed. The flotation foam has to beinjected into the pontoons after the molding process is completed. Such pontoonsare tough, reliable, and versatile for use on marina docks.A suggested field method of addressing water filled polyethylene pontoons is to drill1 inch diameter holes vertically up through the bottom of each pontoon shell about 2inches diagonally from each corner. This will allow water both inside and outside thepontoons to equalize. The bottom of the pontoons will be several inches below thewaterline, so no fuel, oil or other chemicals floating on the surface will be able toenter the pontoons and gradually “melt” the foam. This is an easy, effective, andinexpensive method to stabilize older “puckered” plastic pontoons as well as newerones that may have taken on water. Since the primary function of the pontoon shellis to protect the foam core, drilling holes in the bottom, well below the water line,does not diminish the integrity of the shell or the foam. Do not drill drain holesthrough the sides of the pontoons.The above commentary gives clear evidence as to why pontoons should not bepartially filled with foam. If water gets inside a partially filled pontoon, the foam coremay very well float to the top of the pontoon shell, allowing even more water toAppendix A -- Section C Commentary - Page 84