Stern screw for a vessel as well as a vessel provided with such a stern screw

A stern screw for a boat comprising a stationary tunnel tube in which a propeller is provided which rotates about a shaft in said stationary tunnel tube, which propeller is driven by a drive motor at least during operation, wherein the tunnel tube has an inner cylindrical surface extending in a longitudinal axis direction, and an opening which extends through said tunnel tube in a direction transverse to said axis, said opening receiving therein an intermediate part, the intermediate part extending into said opening and comprising a first side which includes a partially cylindrical surface which adjoins said inner cylindrical surface and is configured and dimensioned to combine with said inner cylindrical surface to form said tunnel tube, said intermediate part being provided with a flange at a second side for fastening to an outer side of a stern of the boat, said flange comprising a first length extending from said first side in a direction substantially transverse to said axis, and a second length extending from said first length in a direction substantially parallel to said axis, and said intermediate part comprising a cavity in which a drive shaft is accommodated which is coupled to the propeller at one side and to the drive motor at the other side, said drive motor being placed at an inner side of the stern.