A plurality of fiber layers is stacked to form a fiber insertion extending in a longitudinal direction of the shell part to be manufactured, whereby a core element having a tapered edge section is arranged along the fiber insertion. The fiber layers are stacked so that the tapered edge section of the core element is wedged into the fiber insertion. The core element is composed by a first and a second core part that are arranged along each other. The first core part forms at least part of the tapered edge section of the core element. The surface of the first core part has a higher permeability to liquid polymer than that of the surface of the second core part so that, during infusion, liquid polymer penetrates the surface of the first core part more readily than it penetrates the surface of the second core part.