PURPOSE: To prevent a bearing member installed in a stuffing box from suffering eccentric abrasion by fitting said box rigidly to an inboard end of a stern tube made of fibrous reinforced plastics.

CONSTITUTION: A stern tube 14 consisting of FRP is liquid-tightly jointed by means of a weather strip 15 to a rear keel 8 of a hull 1 and a bulkhead 3. Further, a stuffing box 16 is in close contact with the inboard end of a stern tube through O ring 36. The stuffing box 16 is also fixed to a fixed ring 27 of the hull 1 by means of a stern tube 14 and a bolt 32. Accordingly, a load of said box 16 is not transmitted to a propeller shaft, and a bearing member 21 as well as a packing 22 are prevented from suffering eccentric abrasion.