Here is detail on the spacing and support. From top to bottom: The top board sits on a crosspiece hanging from the roof/sail loft. It has enough clearance to be withdrawn straight back. The board below it, however, is so tightly placed that it can not be pulled straight out, as the front footstraps would hit. The board slides sideways. Same for the two boards below it. Because I use the second lowest slot for heavy boards (currently a Bic Techno) I've put an extra support on a hinge on the lowest rack. This let's me drive on bumpy roads without fear of excess stress on that free-floating cross piece.