What happens? I was just thinking about 5 fin convertibles and switching around fins and twin fins on a HPSB popped in my head. Certainly this has been tried before, but I’ve never done it.
As I understand it, a pure twin fin cant would be straighter than a standard thruster side fin, but would it effect the ride that much? Also how come we see twin fins as swallow tails, fish tails, or pin tails, but never a squash?
Looking to be taken to school.
The standard position for the sides of a thruster combo put the trailing edge of those fins at about 11". That’s (arguably) too far forward on the rocker for a twin set. If you were building a twin you’d settle for 8"-9", and a couple shapers go to 7", which still puts the center of effort further forward than for a thruster cluster.
If you want to try a twin at the thruster positions you can add a small tail dragger in the rear finbox but I think you’ll still end up having less drive than if the twins were mounted further back where you stand.
I may have it wrong, but IMO the way to consider fin setups is to start with the stance you intend to use and then position the cluster and the rocker to support that. I believe you will have more leverage and control when your rear foot is directly over the center of effort for the fin(s).
Never realized Twin fins were closer to the tail. I thought they were in that 10-12" ballpark too. Thanks for that.
Now how come never a squash?
The amount of curve in the rear quarter has more to do with the way the board surfs than the shape of the last 2" which comprise the tail block. Swallow tailed boards tend to have a straighter line through the rear quarter. All running a squash with a twin means is that the board will have a little less drive from the rail (due to the curve in the quarter) and be a little looser (due to the softened corners) in a pivoting turn. Neither of which a twinnie really needs due to how loose they normally run.
Another thing about boards built as thrusters is that they normally run more tail rocker than boards built as quads, twins or singles. Thrusters don’t really “work” unless you’re actively working the cluster, whereas quads and twins can be surfed more passively.
The twins with the rounded tails normally have their wide points forward, which straightens the rail line a bit at the rear. Those will hold better when there’s more energy in the wave and be smoother in the turns but they’ll be a bit less lively.
Every design is a compromise. You’re always surfing the entire combination of design elements that are working together to create the operating paramters of the board. Not just one or two elements.
woah, That thing looks like a fighter jet.
So reverb, those twins are closer to the tail than a thruster side fin?
Twin fins must be back with less cant and less toe in than side thruster around 3.5" back for short boards. No problem to put them on square tail. Twin set up back work on many kind of design, like a quad with less drive and projection at end of turn, more free feeling, good for front foot surfing and so forward wide point board like describe Gdaddy.
Hi DublAK2; seems many here confuse things exactly the same way than when say “single fin surfboards”. You asked about a thruster shape with a twin set up and that is not the same as a 70s twinnie or early 80s with small surf and planning speed as design characteristics.
So this is for modern surfing (AKA thruster shape) but a bit loose in that way the bottom contour and rocker are very important if you STILL want to have the normal grip if not all is good too…but loose.
The fins are not like the 70s but more upright and sometimes very flexible on the tip. Yes, go a bit rearward than the thruster.
Man you need to try to figure out with those photos.
Hope that helps
You wanted to be “schooled”? Well you have just got an education from gdaddy. All college level insights and info.
My recent summer board build is a thruster/twin option.
I used Greg Griffin twin fin placement numbers, size, and template. So, the twins are WAY back compared to other twins.
As a thruster, it’s predictable, controlled, and a great board.
As a twin, it’s FAST and loose and projects further around sections but it is sometimes unpredictable for me
I surfed it a few sessions as a twin and the last half-dozen sessions as a thruster…
might switch back to twin for a few sessions.
I feel that it could be awesome as a twin if I were able to adjust my timing.
I will try to post pics if anybody is interested
Greg Griffin has never stopped making high performance twins. His design theory involves flat tail rockers, flat bottoms with a very little vee and the “Hawaiian” style rails that are round with a sharp edge for release. He mounts his twins way back, (like @ 5") and he uses shorter fin templates with no recurve in the trailing edge, not the tall MR-style twins. He hand foils his fins out of G-10 to be very stiff so they won’t flex very much under load. He aims his design to favor a heavy rear foot.
Having swapped out in the water with guys and surfed a couple of them, IMO those boards do not surf anything at all like an MR-style twin. I found them to have a really nice balance of drive and control but they’re also pretty unforgiving in terms of stance and rear foot placement. You would definitely need to surf the board as intended in order to enjoy it. There’s been a lot of online feedback for these boards, generally breaking down into people who love them vs people who hate them.
WRT to my last, I’d like to clarify the point that there are different ways to set a twin up, and that it will go better for you if you pick a setup that fits your stance and style, or at least how you intend to surf the board. FOR ME, GGs setup has some advantages but I personally find the placement to be too extreme for the softball conditions I surf and my style. I like some of the other elements very much and incorporate them into other boards that I build, though.
I do like his fin designs a lot. I mean, look at his foil; you’ll stuggle to find retail finmakers who consistently operate at this level. And it takes a fair bit more effort to foil G-10 than for the PE-resined fins. A few of the regulars here who do G-10 fins can attest to that.
Anyways and back to the topic… rider style, stance and ability comprise the starting point for choosing a design, followed very closely by the conditions in which you intend to surf the board. Form follows function, yada, yada, yada. .
