I rarely log...maybe 5-10 times a year...but really enjoy the rush now and then of going fast on a 9 foot board. Not interested in nose riding at all...lined up, semi hollow waist - chest high waves, slotted, high line kind of stuff. Since i wont longboard enough to really dial stuff in, i'm interested in how these fin setups might ride. So far the only one ive used is the single squirrel fin and find it really springs you off the bottom and shoots you down the line. board is HP 9' x 22 1/2" X 2 3/4" Setup one- 9" squrrel fin:Setup two- 3.25" side bites, 6.5" cutawaySetup three- 3.25" side bites, 7" takayama off an old single fin egg:
I have a fin similar to the squirrel fin on my 9-0 Bing Trimulux (single fin only) and it is the bee's knees for everything from mushy crap to solid chest + fun surf. Since you have a 2+1 you may also want to try 4.5" sidebites with a 4.5" trailer for a true thruster set-up. I have found large-wave nirvana with this setup on my 9-4 Soul Performance speed log. Nice hold on steep faces and great tight (for a longboard) turns. Of course when we get head to overhead surf, you will probably grab a shortboard and leave the log alone in the garage pining for you to return. . .
The 2+1 has really been a misused setup. Unfortunately, it's been a real magnet for guys that think that want the latest gadget or (never having a single fin) think that a single fin either can't turn or is for geezers. The truth is, with the right shape, 2+1s can enhance performance.
Personally, I think they require a "performance" longboard shape, with a narrower tail and some "V" for transition from rail to rail. I also think that (using it with the right shape) a 2+1 setup is ideal setup in steeper waves (OBX). While some may use 2+1s on a noserider, putting that setup on a wide, flat-tailed & soft railed board is a waste of money. Soft rails provide all the hold you need in steep waves and if you want to crank tight turns, the noserider just isn't the tool for the job.
All that being said, I think, of the three, that the squirrel fin is best for what you plan to do with it. The side bites will induce more drag than benefit for taking the high line and drawing a line down the face of a flatter (i.e. semi-hollow) wave. Personally, I'd put a Greenough 4A and lose the side bites for that. Just my 2 cents.
Oh...and to sorta echo what Mikey said, my 10' Cluster V has 5.5" sidebites and 3" trailer. On steep, juicy waves, that board can pull off some incredible stuff. Tiny tail, though, and good amount of "V".
I'm going to have to both agree and disagree with Ray... for what you want to do ditch the sidebites, and stick with a single fin... whatever you like in terms of size, flex and template. I have had great success with 2+1 setups on HPLBs with concaves... sometimes in combination with vee, chined rails, etc.... but always some kind of concave. Thin, light, rockered out longboards with shortboard rails and concaved bottoms work well with sidebites and the right sized center fin. The cutaway in the pic is too small, IMO. My all time favorite setup for an HPLB was a 8" cutaway with sidebites on a board with deep double concaved vee. Yes... the tail did slide out on hard turns, but that's what I liked about it.
But getting back to what you want to do... high, speedy trim line in medium sized surf... go with the dragless feel of a pure single fin. You don't need all that tip on the squirrel tail fin if you don't noseride. But if you like that feel, go with it... or try a Harbor fin.... lots of rake, lots of tip... lots of leverage. Flex fins feel great, too, and I recommend getting one just for fun. I like the Josh Farberow Flex Fin over the Greenough... wider template and tip. But maybe that's because I'm a bit bigger than average.