A welding boat for a pouch has a center part and two prolongations extending therefrom in opposite directions and tapering acutely. The welding boat has an opening for the filling of the pouch with a substance in manufacture and inlets and outlets for the actual use of the pouch. The center part is substantially filled by an opening with a lumen which is as large as possible and preferably circular, and the side edges of the side prolongations contact the opening tangentially.
