shaft-tube

from The Century Dictionary.

• noun In ship-building, a water-tight tube extending from the after end of the shaft-alley to the exterior of the vessel, of slightly larger diameter than the tail-shaft of the screw-propeller which it contains. At the after end of the tube is the stern-bearing, and at the forward end a bearing and a stuffing-box around the shaft to prevent the entrance of water into the vessel. In wooden vessels the stern tube is of bronze and is embedded in the after deadwood. In iron vessels it passes through and is fastened to the floors and framing, and in single-screw ships through the sternpost, which is bossed out to receive it.