Whoa! Hold off on sanding those thwartship bands off. Although they are too thick to be scale, there ARE steel bands, not beams, across the hatch covers on top of the canvas, These are to hold everything down, not to support any loads that may be stowed on top of the hatch.
To sum up, starting with an open hatch:
Steel beams fit into notches inside the hatch coaming.
Wooden hatch boards cover the opening, supported by an edge on the steel beams and an edge all along the inside of the hatch coaming.
Canvas over the wood
Steel bands over everything, hooked onto the edge of the hatch coaming.
Will look for some pictures to illustrate.
Fred
Note the steel bands over the canvas hatch cover. The canvas is probably dark green, but looks darker because it's wet.