My Blurr is a thruster w US box, I like the stock fins best for solid surf. I often try Quobbas L side M center, I like how this feels loose, but I feel like there is less drive and my tail can slide out when I don't want it to. I was going to try the infinity stock as side fins w the M Quobbas as center. I assume guess and check is the best way forward, but is there some theory to how the side and center fins contribute separately to the feel of a board - do you want the same fin shape for the center and sides, quobbas has narrower base and more rake I think. I know on quad the mixed shapes common and I dig my Controller quad on groveler. Cheers

I always mix my fins up ,in size flex and shape .I do like shaper fins best ,but every board is different ,my flow I Like flexy sides AMI 1 ,2,OR 3'S and harder stiffer rears for drive ,if you like drive stiffer fins will give you that , .but can be a handful in chop ,I find large or 120 in depth fronts and small 3' rears suit most of my boards as Quads ,
I do see some sets of thrusters now are sold with two rear fins large and smaller ,so yes I would play around with the size till it feels right .once set I never change them again .I will use a knubster at times too ,I take a bag of fins and will change them 2-3 times on the beach till I get it to feel right ,coming in each time to change them .a pain but once set ,I never change that set up .I just get use to surfing it in all conditions .

I even find some of my old Naish rears work perfect ,

For me, the sides provide the hold and speed generation, the rear(s) the control.
Twin fins are thus faster but with less control.
Singles are slower but better control.

Also, I rely more on sides at the start of the turn, and the center on exit.
So if you feel you lack "grip" entering the turn, enlarge the fronts
If you feel you kind of track and cannot tighten your turn, reduce the rear(s)
If you tail-spin-out, enlarge the rear(s)
...

This said, there is no "optimal" setup, it depends on what you want.
For instance, with my board with the thinnest rails and faster rocker, I reduced all the fins to get the maximum speed.
I thus rely on the rails at speed for the hold more than the fins.

But on short and fat boards for slow waves, I will put huge sides to push hard on them and hold even at low speed.

Thanks for replies - tried the setup in picture, waves steeper and bigger than expected, tail was sliding, swapped back to the infinity in center. Hard to directly compare cause by the time I got back out the sand bar stopped working and I surfed a softer wave. Hard to dial this stuff in on beach break w big tide swings.

I really like a small trailer with large sides when you want to turn the board from further up but I used an even smaller 3'' trailer. In juice where you might want to push hard on the back foot I had same result doesn't hold or drive. You can try moving the small rear further back, but for a thruster to work as a unit I don't like it too far apart.

Select to expand quote

Kisutch said..
Hard to directly compare cause by the time I got back out the sand bar stopped working and I surfed a softer wave. Hard to dial this stuff in on beach break w big tide swings.

For this you have two solutions:
- with an US box, use a tool-less center fin (either FCSII or a finjak), so you can move around the rear without going in.
Moving a bit the rear fin makes a lot of difference

- bring a spare fin. I could put 2-3 fins in the pocket formed by my chest zip in my wetsuit, and it was easy to switch FCS II fins on the spot.Invaluable input to switch fins between two waves.I guess you can also change screwed-on fins with some practice and a bit of rope as a key leash, e.g. key leash around your main wrist and key tucked inside the wetsuit when not in use.

I have a few finjacks but they don't work in my Infinity box, too tight of a fit for the finjack to close, it's annoying.

Select to expand quote

slsurf said..
I really like a small trailer with large sides when you want to turn the board from further up but I used an even smaller 3'' trailer. In juice where you might want to push hard on the back foot I had same result doesn't hold or drive. You can try moving the small rear further back, but for a thruster to work as a unit I don't like it too far apart.

Yeah there seems to be a threshold where I much prefer the larger stock fin. I'm feeling anti-quiver right now, wanting to only surf Blurr so I'm more dialed in when it's good. That led me to adjust fins instead of switching boards as conditions change.