What was a grating used for?

Ships had such wooden lattices to avoid slipping on water or ice when walking through a doorway. It also made it easier to stride over the lower door threshold.

The origin of the word “grating”, meaning “partition or frame of parallel crossing bars,” circa 1620s, is grate, meaning “iron bars or cagework across a door or window,” from Anglo-Latin (mid-14th century), from Old French grate or directly from Medieval Latin grata, meaning “a grating, lattice,” from Latin cratis, meaning “wickerwork, hurdle”.