Slab said..
I tried my board ( further up this page) today with three same size XL thruster set up. It was awful....so slow to paddle and slow on a wave and sooo much harder to catch the waves. Very noticeable...actually came in early as I found it so frustrating. Back to 2+1 (7 inch plus 3.5 or 4 inch sides) or a 10 single.

Yup, found the same. You need to decrease (a lot) the center fin size.

I have been trying these out on my 8'10" Flow over the past few days.
The sides are smaller than I'm used to, but I have been a fan of a smaller centre fin in a thruster set up for a while, and was hanging to have a go.
I have lucked out on days off vs waves timing for quite a while, but hit the jackpot this oz day weekend.
Been on some steep, true 4 to five foot faces over the last couple of days, with some quite exciting 5c/50c moments, but these fins held 100kg+ on a 31" wide board on the wave really well.
Managed to get the foot back on a triple section bomb this morning, and was impressed with the hold an release.
Two thumbs up.

What's a great ocean distance paddling fin to put in the travel fin wallet, to get more cruise out of allround hire boards ?
We were doing the 8km loop from airports to Jimbaran at back of the break ,returning across the bay. Felt we needed something better than single 8" surf fins.
Thanks

Thanks DJ ,
found your informed post on FCS2 center fins,
Going a dolphin and a touring fin.