Tunnel

— Shaft-tunnel. A watertight structure from about 4 to 7 feet in height and somewhat le in breadth, according to the size of the ve el, fitted at the middle-line, upon the floors in small and middle size steamers, but elevated upon supports from 3 to 8 feet above the floors, in large and very large ships; extending from the engine room-after-bulkhead, to the stufflng-box-bulkhead. It encloses the screw shafting, to which acce is obtained through a watertight door in the engine-room-bulkhead In twin-screw-steamers the tunnels are placed near the sides of a ve el. See Plates 25. e & 43. 24.