Currently there is a lot of interest in Quads. As well with many quad setups a center fin box is being installed for also running thrusters. I keep getting asked about drag or turbulence from the unused box or boxes depending on the setup. I know on 10.5" longboard boxes there is quite a bit of opening on either side of the fin. I have never heard much concern about this. Would love to hear opinions on this from the experts and anyone else as well!
Dave_D
I was thinking this very thing when I tried out my new 4/5 fin. I rode it as a quad with the center plugs open. I can’t imagine that they are an issue, but some may think so. Maybe on a wave where you need every ounce of speed you can get it could be a factor.
DaveD
I would tell them that there’s no way to measure it except ride it. But if they want a quad, they don’t need a box. If they want 3 boards, tell 'em to ante up! 
greg
edit: With ref to Surfthis’ photo, I don’t think the small size of FCS plug holes could add any perceptible drag
i doubt if there’s really THAT much drag created by an opened box. with no flow-thru, once water is trapped in there, passing water would simply deflect. it’s like the “bubble of air” created in the back of a pickup truck when the tailgate is up, such that (contrary to popular belief) there is less drag when the tailgate is up as opposed to down, resulting in better gas mileage.
did anyone else see that episode of mythbusters on the discovery channel???
My old Chevy P/U truck got at least 5 MPG better mileage highway with the tailgate removed and placed in the bed, than with it up.
YMMV.
With respect to holes in the bottom of the board, I’ve ridden it both ways, many times, and never noticed a difference. Princess and the Pea might though…
This is actually true, the tail gate down to get better gas mileage is a myth. It’s been tested and confermed (by others and by mythbusters)
Old trick from windsurfing,
use clear packing tape over the box,
try it with and then peel off to check without.
Let us know how it works,
Pete
Soulstice, i saw the episode… (i love that show)
the flow test that they did in the water with the model truck
really applies here don’t you think?
for those who didn’t see the episode (from memory),
they put a model pickup truck in a flowing current of water
facing into the current. then they introduced some particles into the
water. the particles flowed with the water all around the truck.
some of them landed in the bed of the truck and didn’t come out.
the particles flowing with the current went over the cab of the truck
and almost straight back. it seemed there was a “bubble” of water
in the bed of the truck that was pretty motionless and kept the flowing
water from entering the bed and creating drag. the bed of the truck
is pretty close to the shape of an FCS box hole.
IMHO i don’t think that empty FCS plugs are creating that much drag.
not enough to feel at least.
I’ve got some red-X caps they make for their plugs. Mr. Yater gave me some tapered material to fill the void in the center box. I never really knew if it helped or not, but it felt good trying an idea that had some thought behind it.
The difference in drag is negligable, I’m sure. I agree that once the space is filled with water, other water passes right over it without much fluid friction. It actually might be faster… One theory is that sanded boards are faster than polished boards because, at the molecular level, water passes easier over the water trapped in the tiny grooves of the wetted surface than the acutal surface itself. That’s one reason why sharks have sandpaper skin… it helps them swim faster.
But, you could make some tabs and pop them in when you don’t use the plugs. To take them out, screw a small screw into the top of the plug just far enough to get a bite, and use the screw as a handle.