An engine room arrangement for a marine vessel comprises a fin formed at a rear portion of a hull of the vessel. The fin projects downward from the hull and protects a propeller of the vessel. A gear box is arranged at least in part in the fin and transmits a rotation of a propulsion shaft coupled to a main engine to a propeller shaft drivably coupled to the propeller. The fin provides extra buoyancy for the vessel. The propeller shaft is formed as a relatively short shaft, while the propulsion shaft is formed as a high speed/low torque shaft having a smaller diameter.
