The Stacker Kayak Rack from Thule

        Do you need to carry one or more more kayaks in the absolute smallest space possible? With the Thule 830 Kayak Stacker you can carry up to four kayaks on their sides, making the most out of your roof rack. The Stacker comes includes all the load straps and bow/stern tiedowns you'll need to carry one boat, so if you need to haul more than one kayak, make sure you purchase enough tiedowns for your other boats. We also recommend using Thule 556 Rack Pads to cushion your kayaks where they rest on your roof rack's crossbars.
    The Stacker features sturdy scratch-resistant steel and impact-resistant plastic construction. It will fit Thule and Yakima rack systems right out of the box, as well as most OEM factory racks. Installation on thicker crossbars may require the use of Thule's Xadapt3 longer bolt kit. The Stacker can be folded down flat when not in use to reduce wind resistance. The integrated ratcheting hinge system ensures that the Stacker is locked in position, so you'll never have to worry about your kayak racks collapsing, or having them flop around in the wind and bang on your roof.  Not only is Thule's Stacker a space-saving kayak rack with an aerodynamic design, it's also very economical. Just try and find a set of kayak saddles that can carry four boats! On second thought, don't. It would just be a huge waste of time you could better spend out on the water!