Kayak stackers are designed to help you carry 1-4 boats up on edge using your vehicle's roof top crossbars. Stackers are a good budget-friendly way of taking multiple shorter plastic boats and are commonly just used for white water kayaks. Longer boats and boats that need more support should be held in J-style kayak cradles if you need to side mount them.
Racks For Cars sells kayak stackers at each of our two Edmonton, Alberta, Canada retail store locations. Kayak racks ship for free across Canada on orders over $150.