Save Fuel by Putting your SUP on the Roof - This Way Up!
Ever seen a kook strapping a board onto the roof of his car the wrong way around? Well the ‘right way’ differs depending on who you ask. To them, it might be correct – and you’re the kook! But finally, someone decided to reach out to a professor of Aeronautics and find out the most streamlined, aerodynamic way to strap a surfboard to a cars roof racks.
Dr. Paul Dimotakis, Professor of Aeronautics and Professor of Applied Physics at Caltech knows a thing or two about the way air flows over a moving object, and air at 100kmph exerts a surprising amount of force. So when you consider a surfboard is sitting on top of a car, copping that kind of abuse every weekend, (for some of you every day) it’s important to do it right. Not only for your boards sake, but your wallet. Extra drag = more fuel. More fuel = less money for SUP gear.
His opinion is that;
"Nose first is preferable. If there’s any side wind, having the tail (fin) in front would increase drag more than having it in the rear because the flow would separate at the fin and it’s better for it to do that aft.”
Now that’s getting into the 0.000001% kind of efficiency (which is important in an aeroplane) but not exactly critical to liters per kilometre.
This however, is!
“If the nose faces forward, it’s also important that the noses tip is down (as you’ve sketched), again to minimize flow separation since the flow has an upward component as it’s going over the car and one would like the board to conform with that to the extent possible.”
Keeping the SUP as conforming as possible to the car might mean the difference between 2 and 3% efficiency at highway speeds, resulting in 10-15 extra kilometres per tank in your average surf mobile; plus it might save you a board which is damaged like this one!
So next time you put your SUP board on the roof, nose first, upside down. Professor Dimotakis says so!
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