TM 55-07/NAVSEA OP 3221 Rev 2
(5) With the increased use of power-operated folding hatch covers on merchant ships, breakbulk ships that use tween-
deck hatch boards are encountered infrequently. However, vessels that use hatch boards are still in operation under
foreign flag and should be considered. When flooring is required, construction shall conform to figure 7-7. In most
cases, however, wood pallets are loaded directly on the hatch boards, as shown in the figure. Chapter XVII of
29CFR1918 requires that, when mechanically powered vehicles are used aboard vessels, adequate provisions must be
made to ensure that all working surfaces can support the weight of the vehicles and loads. Hatch covers, truck plates, or
other temporary surfaces should not be dislodged by movement of the vehicles. Therefore, as a minimum, a double
layer of 1by 6-inch lumber should be installed over the hatch boards with the top course laid crosswise to the bottom
layer and nailed to prevent free movement. Plywood at least 3/4-inch thick or a single layer of 2-inch lumber may be
used. However, in all cases, the bottom layer of 1-inch material, the plywood, or the single layer of 2-inch lumber will be
laid with its longitudinal axis parallel to the center line of the vessel.
Figure 7-7. Comparison of flooring over hatch boards with stowage of wood pallets directly on hatch boards.