empty flatbed aerodynamics

[Nordby]

I towed an empty 30' gooseneck flatbed to Santa Fe this friday. I know, a sin to dead-head like that, but I wasn't organized enough to find a one-way load to offset fuel costs, etc. A friend his loading it with hay and bringing it back to Colorado for me (via Alamosa).

I noticed driving into a headwind at 75mph that I could feel the gusts, not just the weight of the trailer. I could confirm this by watching the boost and egt rise to compensate for the headwind changing - it felt an awful lot similar to driving a trailer with an obvious wind footprint when the wind would grab it and make the truck work harder.

Looking at the trailer the next day, on a few of the weathered boards there were some splinters of decking coming up. They were picked straight up, 90 degress from the deck like a small spike - rather than bent over and more parallell to the deck like I would have guessed they would by 75mph wind going down the road. I'm theorizing that this is a real similar situation as putting your tailgate down and getting WORSE mileage. The wind comes over the cab, and hits the long flat wing created by the bed/horizantal gate causing friction/resistance. In my case, I had a 30' bed of perfect flat for the wind to grab, causing friction and making the truck work. I'm thinking if I put a couple of bales of hay on it in a few spots to spoil the aerodynamics of the trailer it would pull 'empty' much nicer.

Am I making this up, or have others seen/felt this before? What else is at work here that might be inefficient - is that trailer acting like a big wing and the wind going across it lifting it, but not causing friction?

Thanks for any input - just curious, and will put a couple bales, or 4x4's, or something on it if it happens again that I have to pull it empty at high-speed.

thanks,jon.