half deck

(in a sailing ship) the portion of the deck below the upper or spar deck and aft of the mainmast.

Origin of half deck

First recorded in 1620–30

half-deck·er, noun

The beams of the main-deck are of American or German oak, those of the lower deck and half-deck of pitch-pine and Norwegian fir.

The South Pole, Volumes 1 and 2 |Roald Amundsen
It doubled her security in this particular, more than answering the purposes of a half-deck and wash-board.

Afloat And Ashore |James Fenimore Cooper
After a while he went to the half-deck and knocked at the Gunnery Lieutenant's cabin door.

The Dreadnought of the Air |Percy F. Westerman
Mr. Markitall went down under the half-deck to make the inquiry.

The Pirate and The Three Cutters |Frederick Marryat

And in a moment his four companions were standing up on the boat's half-deck and gazing out with searching eyes across the ocean.

The Golden Galleon |Robert Leighton