A method for manufacturing a shell includes providing a mold of the shell. The method also includes forming one or more first skins on the mold. Further, the method includes securing at least one three-dimensional (3-D) grid structure onto an inner surface of the one or more first skins. Thus, the method also includes securing one or more reinforcing members to one or more locations of the grid structure so as to locally increase a stiffness of the shell at the one or more locations by creating one or more localized sandwich structures with the grid structure.