To ensure noise prevention in a ship and to facilitate inspection work for an internal combustion engine through an opening formed in a hull by forming the opening in the hull so that the internal combustion engine housed in the inside of a ship can be inspected from the outside of the hull.

A propulsion internal combustion engine 16 is housed inside a hull 3. Above the internal combustion engine 16, a seat supporting base 42 is formed in the upper part of the hull 3. An overstriding type seat 32 is arranged on an upper plate 45 of the seat supporting base 42. In the upper plate 45 of the seat supporting base 42, an opening 49 communicating the inside of the hull 3 to the outside for inspection of the internal combustion engine 16 is formed. Between the seat supporting base 42 and the seat 32, a cover body 50 closing the opening 49 freely openably is arranged independently of the seat 32. The seat 32 is supported freely removably to the seat supporting base 42 and/or the cover body 50.