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In iron ship-building, noting a type of freight-steamer in which the side is carried up amidships above the upper deck to form a bridge-house closed by a bulkhead at each end. There is a forecastle deck at about the level of the bridge-house, and the upper deck between them is inclosed at the sides by high bulwarks, thus forming a sort of pit or well. To let the sea-water run out of the well, large freeing ports are cut in the bulwarks.
The Century Dictionary (Public Domain)