That sounds like typical condensation. Two grooves implies Gebo hatches, and the frames are aluminium, so conduct heat well, which means they're prone to condensation if it's moist inside the boat and cool outside.
If you're not normally opening the hatches, you can effectively "double glaze" the hatches for winter by spanning some clingfilm over the inner frame (gotta tape it up first or it won't stick), which vastly reduces the problem.
In port we'd use a dehumidifier to remove air moisture from inside, although if it's very cold outside you still get condensation on the hatch frames due to the temperature difference. The clingfilm or any other insulation stops that.
