While browsing different car-top rack options a question came to mind. Would you recommend a fairing or not? Is there a benefit to directing more wind up towards your boats, or wouldn’t it be better to just let it blow between the boats and the car top?
my $0.02
I don’t think anyone knows for sure, or can present anything beyond anecdotal evidence.
My own instinct tells me that a simple flat plane won’t do much to clean up the aerodynamics or to calm down all that turbulence. The air still has to go somewhere.
What Slush said
I agree with what Slushpaddler says. I always assumed fairings were an answer to some problem (noise?), but I never knew what it was.
Fairing
On my setup the fairing cuts the wind noise considerably when the racks are empty. I can’t tell any difference when loaded. Aerodynamics will differ car to car so as the automakers say “Your mileage may vary”
Depends on the car
Never needed fairings to handle noise on the Ford/Mercury wagons, but the Subie Outback (pre-2010) is unbearably noisy without it. Try it without and mess with distances between the bars. If noise persists badly you’ll likely need to add fairings.
Honda Civic Hybrids: 2005 and 2006
When racks are empty without a fairing - pronounced wind noise; with a fairing - blissfully quiet.
When racks are loaded, without a fairing - no noise issues.
Your experiences, like your vehicle(s), may vary.
Mike
Problem
I always assumed the “problem” that the fairing solved had to do with the manufacturer’s earnings report.
Ditto Mike’s comment!
Yes, without a boat up there, most cross bars will whistle horribly. The fairing eliminates that.
noise
You can wrap the bars in corded tape with tape over it (think hockey stick grip) to stop the whistling. A lot cheaper than the $75 piece of plastic that thule and yakima sell.
We have a WINNER
Is it the rack or
the anemic growly engine, or rattling exhaust heat shields??? Just kidding.
To fairing or not to fairing
Ok, thanks for the replies. I guess I’ll try it without and see how it sounds and go from there.
Have had the heat shield thing 
but the diff in noise from the roof was the rack. Same racks exactly between the two cars, cross bars and stackers, but somehow the Subie managed to be way noisier with that stuff up.