Hatch cover steel structure
For stable and smooth operation of the hatch covers on board, the panels should be stiff. However, to maintain weathertightness at sea, the steel structure of a hatch cover, as well as the bearing pad and sealing arrangements must adapt to the varying shape of the coaming top while the hull is working and flexing at sea. The optimal stiffness of the steel structure of a hatch cover panel is a compromise between the above issues. The correct stiffness is achieved by selecting the optimal proportion between the open web and box construction, the double-skin construction being the stiffest design.
Keeping the deadweight of the vessel under control and maintaining the stability calls for the use of high tensile steels in the main members of the hatch covers. In case of container ships, the size of the containers dictates the arrangement of the main girders carrying the loads and conveying the forces from the hatch cover to the coaming and hull structures. Keeping the structure simple, i.e. the number of components optimised, promotes production cost efficiency and facilitates the production of high quality surface treatment.