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

The more critical situation typically occurs during low water periods (i.e. low tide)when the relative position of the lower end of a gangway is closer to the edge of afloating dock. If it is necessary to have a gangway “land” near the edge of a floatingdock, supplementary flotation may be necessary under the edge of the dock belowwhere the gangway rests. This extra flotation might be necessary to maintain safeand required freeboard levels and cross slopes under various loading conditions.Full LL on a gangway probably will not occur very often. Therefore, to transfer thefull gangway structural design ULL of 50#/ft 2 to the gangway-supporting dockswould result in “unloaded” docks that ride unnecessarily high in the water for longperiods of time, causing excess dock freeboard. This causes localized differences infreeboard and problems with cross-slopes, especially along those areas that arepart of an accessible route.The above reduction provides a reasonable consideration of both typical andextreme conditions without compromising safety. In the event that a gangway wasloaded with the full design ULL of 50#/ft 2 , this short-term load would spread withinthe dock system. Freeboard would diminish, pontoons would be forced deeper intothe water, and the dock’s structural frame would cause the load to spread to othernearby pontoons that would pick up portions of the gangway load. Any welldesignedand constructed dock system should be capable of supporting additionalshort-term loads that temporarily reduce the design freeboard. Once the higher thannormal loads are removed, the dock recovers and freeboard returns to normallevels. This dynamic action described above can only be tolerated if the minimumfreeboard requirements for floating docks are still complied with.......................................................................F2.5 Minimum Clear Width of GangwaysCommentary:Nominal widths of gangways typically vary from 36 to 60 inches, depending onlocation, expected traffic loads, gangway lengths and special needs.If gangways are too narrow, they can be awkward to use, and people moving upand down a gangway at the same time cannot pass safely and comfortably,particularly during low water periods when gangway slopes are greatest.Conversely, if gangways are too wide, the handrails on each side cannot be used atthe same time if desired and needed. This is important to people with small children,senior citizens, persons with disabilities, etc.Considering the requirements for 1¼ to 1½ inch handrail diameters, 1½ inchclearance between the handrail and the gangway railing posts or other supportingelements, the 36 inch minimum clear width, and the width of the railing structure,the total overall minimum width of an accessible gangway will be about 48 inches.Appendix A -- Section F Commentary - Page 114