Put the slings on the roof rack for the kayak. You should place the first kayak here on the roof rack. Secure the first kayak towards the roof rack using a bungee cord. You should also place the second kayak in the roof rack. Place the second kayak on the ground. Tighten the first kayak's straps. Wrap the kayak straps around the kayak and double-check to ensure it fits and is tight.