The Yakima BigStack Boat Rack holds two boats in a vertical position to take up minimal space on top of your car, so you can also add a cargo box, bike rack, or another BigStack. When you're not driving around with sea or whitewater kayaks on top of your roof, the BigStack Boat Rack folds down to reduce wind resistance and increase gas mileage. This versatile rack works with Yakima round bars, square bars, and most factory roof racks.