So mostly inspired by this thread, I decided to do some similar testing…
I just got back from 4 days at San Onofre, surfing 4-5 times a day, through all tides, in waist to shoulder high beachbreak. For the trip, I made a fin testing platform out of a 10’ surftech, by adding 4 Proboxes in addition to the center longbox. I’d made a 5-box longboard before, but that had my ‘normal’ noserider rocker & rails and I don’t think I was getting everything out of the fins that I could with a different board. I read carefully Randy Rarick’s post about his (signature) Surftech for fin testing on a trip, and I pretty much tried to do the same thing he did. I’ve found that cant angle is radically important to performance, at least in the longboard.
All quad testing was done with the same 4 fins - 4.5" Hanalei paddles front, 4" Hanalei rakes rear. Trailing edges of the fins are at 6" & 12", front toe is 3/16", rear is 1/8", both boxes are 1 1/8" off the rail at the rear mark. Big thanks to Scott at FF&F for getting them (and the inserts) up to me in time. 
With fronts at 8* and rears at 6*, the board would whoosh around in a deep gouging turn - on a dime - like a waterski, when back foot force was applied right over the fins (this is not my normal style of surfing, so it was quite a surprise to feel it). It would also, a little surprisingly to me, noseride very well. Lots of hold. On the downside, it slowed in straight-line trim, like a thruster and didn’t pump for speed at the center of the board very well either. So basically good in the pocket, not so good in a high line or on the shoulder.
With fronts at 4* and rears at 0*, it was a totally different board. Felt like a narrow, raked single fin going straight - very fast in trim and easy to steer from the middle of the board. But also loosened up when I backed up to over the fins & rollercoastered easily. But - no hold or stability for noseriding. Get just past the center and it felt like there were no fins at all.
So then I split the difference and went to 6* & 4*. Predictably, it did a little of all of the above, but nothing very well. If I was glassing on or using a fixed system, it would be tempting to install these midpoints, but it would never be as good a board as it could be otherwise. So the other option is to choose (compromise) with either the noserider/turning quad or the speed quad which obviously brings out one kind of good performance but limits the versatility. Or put in ProBox
I did also try it out as a thruster, generic-looking 4.5" rakes all around (the Probox plastics for the sides), center’s back edge at 5", fronts at 12". Felt as draggy as the high-angle quad, but without the noseriding. No thanks, won’t bother with that one again. I also rode it a few times as a single fin, which was good on the mushier higher tides. Randy said his favorite setup was actually 8* fronts and 0* rears. Unfortunately, I didn’t remember that until I got home & re-read his posts so I didn’t get a chance to test that. Soon, though.
Sorry to ramble, but testing is always fun. And, on a longboard quad at least, cant angle seems to be the most important adjustment. If you can decide which type of performance you want, no need to adjust it. But if you want to be able to tinker with it, put in Probox. Had good conversations with Matt Calvani & Stingray Ray about Probox, and they’re really digging on the products like I am. Great stuff Robin, Larry, et al.
I have more photos of fins in the boxes on the computer at home if anyone wants any…
Sounds like a good trip.
