The invention relates to a service space of a retractable propulsion device or corresponding system in a vessel or corresponding floating structure, which service space (11) comprises a closed or closable space limited by walls, a top structure and a bottom in which an access has been arranged for the crew (C) from the other parts of the vessel or corresponding floating structure. The service space (11) is constructed into connection with the bottom (2) of the vessel or corresponding floating structure so that the propulsion device (4) or corresponding system is retractable from an operating position into a service/storage position within the service space (11) and correspondingly lowerable from the service space (11) down into the operating position. According to the invention, the service space (11) is located at least mainly below a waterline (WL) of the vessel or corresponding floating structure and is provided with watertight closing devices (14) arranged on the level of the bottom (2) of the vessel or corresponding floating structure. When opened, the closing devices (14) constitute a direct access from the service space (11) to water via the bottom (2) of the vessel or corresponding floating structure for lowering the propulsion device (4) or corresponding system from the service space (11) to water into the operating position i.e. operating mode and correspondingly for lifting it from water within the service space (11) into the service/storage position i.e. service/storage mode. When closed, the closing devices (14) constitute together with the top and wall structures of the service space (11) a watertight space from which water is removable after closing the closing devices (14).