The curves were lofted to form a polysurface. When lofted in Rhino it generated several open polysurfaces instead of one single surface.
However it didnt work too well. Back to a framework of two 3 curves and definitions using line segment and pipe components.
The number of spokes or ribs, their thickness, number and orientation are varied using sliders. The height and width of the seating is varied along the z axis.