Create the shell
In project Schematic, double click on Geometry to open the Design Modeler. When prompted, select Milimeter as the unit.
Click on the XY Plane and the z axis to begin sketching. Use the Linetool to create a vertical line starting from the x axis. Hover the cursor around the axis until you see a symbol C to begin your sketch. The symbol C means the line is coincident to the x axis. Next, use the Arc by Center to create the dome of the shell. Hover the cursor near the y axis until you see the symbol C. Single click on the y axis and click again on the tip of the line you have just created. You should see a symbol P when you click on the vertex, which means coincident. Finally, click on the y axis again to finish the arc. Your sketch should look like this: