I have never had the opportunity to work on a ship equipped with this type of hatch covers. Certainly, the designers didn't design them this way without a reason. I wonder what their reason was? . I also wonder whether ships with covers of this type had (do not have) problems with stability in the winter in the Baltic Sea. After all, during severe frosts, in the waters of the Gulf of Finland and Bothnia (and elsewhere), Baltic water with low salinity will certainly freeze in the open, empty spaces of these covers. This may be an additional total weight of up to 120 - 140 tons... In such a case In winter, loads taken by ships of this type should have a rather low center of gravity - steel, metal ores, stones... Loads transported on covers probably only in warmer periods or in water areas where the water does not freeze.