Hatch covers without sealing between comings and panels and with non-weatertight gaps between panels. Such covers can be fitted on board containerships with high freeboard. Hatches within the forward quarter length shall be located at least 6.9m above the designated freeboard deck, other hatches at least 4.6m.
The gaps between panels should be as small as possible and proportional to the capacity of the bilge system, as well as to the capacity of the fire-extinguishing system, and in any case should be not more than 50 mm.
Further reading: MSC/Circular.1081- “Guidelines for Partially Weathertight Hachway Covers on board Containerships”.