Lets take a look at using Rapid-Straps to secure a SUP directly to the crossbars of the rack. This works the same for surfboards or wind surfboards and of course you can stack multiple boards on top of one another…how many? Depends on how thick the boards are.
First the starting point, a factory installed set of crossbars, of course aftermarket work the same.
Start by separating each of the Rapid-Straps by releasing the cam buckle.
Start with the strap that has the cam buckle on it and wrap the strap around the crossbar of the rack and pass the cam buckle through the loop on the end of the strap.
Now pull tight and slide the strap to the middle of the roof.
Do the same thing with the other end of the strap. Wrap the strap around the crossbar and pass the end through the loop.
Pull tight and repeat the process with the other Rapid-Strap on the second, in this case rear crossbar.
When both Rapid-Straps are on the crossbars, place the board on the crossbars.
Now pass the straps over the top of the board and thread the strap through the cam buckle and pull tight.
Tie an overhand knot. This is very IMPORTANT, all cam buckles can slip and Rapid-Straps are made using tubular webbing, which is stronger and more durable than webbing but thicker so tie a knot to prevent slippage. Remember you are responsible for securing your load Rapid-Straps protects your gear!
It is recommended that you use a bowline and tie the front of the boards to a secure point on the front of the vehicle, especially with longer boards over 10 feet long or if the board hangs excessively out over the hood of the vehicle.