Aloha Started a thread yesterday, inquiring about flex fins for singles, and was amazed at the wealth of knowledge out there. If anyone is open to providing a brief history znd/or physics lesson on the flex fin phenomenon, I would greatly appreciate it. Among other things, I am interested in: 1. Who developed the flex fin? Greenough? A number of guys throughout surfing history (i.e. the tri-fin phenomenon?) 2. What are the benefits of a flex fin? My “scientific mind” would tell me that flex fins would create more drag thereby reducing speed, but my point break egg experience tells me that, in smaller glassy waves (head high and under), the fin actually “springs” me out of bottom turns like a slingshot, and maintains or even generates speed when arcing through cutbacks. Just curious. Aloha Kit
Kit, There’s a lot more going on that can really be summed up in a paragraph or two but flexible fins tend to distort with the water flow and thus allow the board to go faster during the turn and bring rail design more into the performance picture. More flex doesn’t equal more power though. Greenough may not have been the first the develope the idea but he sure did a better and more thorough job than any one else I know of. Flexible center fins do have a springy effect as they release. IMHO the effective drive this gives is negligable. It does feel good though. How much flex is in the fin will effect how much drive the fin will give when you really lean on it so if you really want serious fin drive off the bottom moderate tip flex seems to be the best compromise to center fin performance. However there are lots of things to try. The same board will come alive in different condtions when a different fin or fin set-up. Some top surfers prefer rigid fins, some flexible ones depending on what kind of board they’re riding and the conditions. There isn’t a single answer to achieving the maxium edge of fin performance because there are some many different board configurations. Mahalo, Rich
I’d have to agree the the increase in speed has never been there for me however it’s allowed me to carry speed more through bottom turns on my 9’4. I went from an 8" stiff to a 9.5" true ames flex and it’s been a blessing for mid-size surf. Overhead it seems a little too sensitive to trimming because of the increased wave energy, but it’s really a guess. There are far more k nowledgeable people on this board.
Try one of these. From my recent experiences it gives doubleplus spring out of turns…much more that the traditional flex fin. I don’t have any idea why. Search the archives…there’s been a lot of discussion about these. 
The flex fin is 30+ years old. The theory starts with a rigid singlefin. The principal limitation is that the fin will stall when you turn too hard. You see, fins generate turning power by redirecting water that they move through. If the fin is too angled relative to the water, it no longer pushes water to the side - it just sorta mucks it up. This shows especially for people used to surfing thrusters who ride a single. They drop in, turn hard, and fall as the fin loses hold. One way to solve this is to make the fin more flexible. When you start to turn, the water will bend the fin rotationally about its base, and also to the side (in cant). The rotational bending allows the flow around the fin to be less disturbed (more attached, in the lingo), which allows the fin to create drive at steeper angles. The downside, for larger waves, is that the fin will have a tendency to wobble (relative to a stiff fin, or a 2 or 3 fin board), which is particularly disconcerting to some people. Flex fins are making a comeback, I think, because of the resurgence of older technology like single-fins. They lost out originally to twin fins, then to thrusters, simply because those designs allow better turning, and are more stable at higher speeds. Or because the best pros in the world used them, depending on who you listen to… http://www.blakestah.com/surf/
Am looking forward to receiving and trying out your new fin set up. Just received the UPS tracking code so it should be here soon!
Hi Harvey Is there a model name for that fin so I can search for it in the archives? Thanks…
Stage Six Greenough www.trueames.com
Halcyon is correct about amount of flex-too much and you’ll get nothing.moderate seems to be the best.remember too that some materials have a better memory than others and will retain their shape and flex properties better and longer than others eg, volan and g-10, much better than standard glass.
The best flex fin I’ve been able to come up with is one that combines carbon fiber and fiberglass laid up with Greg Loehr’s Resin Research epoxy. He makes one the cures rigid and another that cures flexible. I laid up a 9.0" Greenough Stage IV and a couple other 9.0" templates for big waves testing in Hawaii and with his flexible formula the fins have the same kind of spring that a graphite fishing rod has. Being an avid fisherman all my life I just applied my knowledge from all the rod building I’ve done. Regular fiberglass rods have very slow recoil. Graphite rods are much snappier and livelier. It’s the same with surfboard fins. Most of the templates I use can be foiled to accommodate this kind or recoil action. It’s very quick to get back to where it was and so it makes for a very lively feeling under foot. If you have enough rail power under you real soft flexible fins are fun but when you really want to crank a bottom turn in steep surf you need something that has lots of life, power and a very quick memory. Good Surfin, Rich
Properly made flex fins, positioned correctly on a compatible board design will not stall when driven thorough a severely banked rail turn… instead they release, often resulting in a burst of speed as the fin breaks free of the wave`s surface. Boards which function best with flex fins generally have fuller templates, rolled bottom contours and softer rails which work with the fin to provide hold. A good flex fin, when carved hard, will release and re-enter the water smoothly. Like anything else requiring higher levels of sophistication, flex concepts, in board and fin, take a lot of time and effort to get dialed-in right. 30+ years later, that journey is still worth the price… regardless of what the best pros in the world happen to be using. 
Dale, so true about how the hull, and rail and rocker work together with a flexfin on stubbies or fuller outlines.It is hard explain if you havent banked one over and felt that horsepower.
sounds interesting Rich-what’s your e-mail again?thanks.
thanks…