So just what is the right way up for a kayak on a car roof?
Traditionally, most of us chuck kayaks upside down onto roof racks. It’s the only option if you don’t have J-bars, uprights or a cradle. But it’s by far the worst option aerodynamically. When you think about it, all the air hitting the windscreen of a moving vehicle is deflected upwards, meeting the flat surface of the kayak deck. This mass of air enters the open cockpit, fills the boat and causes cavitation, creating even more drag – a bit like having a plastic parachute attached to the roof of your car. So, contrary to what you might think, it’s a good idea to use a cockpit cover (even when mounting the boat upside down).
For sea kayaks and touring boats the best way is usually to mount the kayak upright in a cradle: the air then meets the slipstreamed V-shaped hull of the kayak. You definitely need a waterproof cockpit cover, otherwise the boat will fill with water should it rain. If more roof space is needed, compromise with the use of J-bars to angle the kayak. Either way you should always use tie-downs (see Tie Down your Kayaks article).
Whitewater boats are more open to debate, but I would argue that the squat profile and flat bottom of the boat means sideways mounting against an upright is probably best. If you put two boats with cockpits facing one another, then you may get away without needing cockpit covers. Side mounting also saves space on the roof rack, allowing more boats to be carried (though this does make the car more vulnerable to side winds).
So, the right way up for a kayak when shifting it about on a car roof depends upon the type of kayak and how many kayaks you need to carry. All we can say for sure is that upside-down is never a good idea, but cockpit covers certainly are.