fin flex article (lengthy)

A Matter of Degrees: The Magical World of Fin Flex
by JD Jenkins

A hand carved dolphin hangs in Stanley Pleskunas' home, arcing over a plate glass window that takes in a fine view of the Elkhorn Lagoon near Moss Beach, California. The nearly life-size piece shimmers with deep wood grains through finely sanded skin. Shaped by Stan himself, the creature is topped with the unmistakable outline of a surfboard fin.
When it comes to invention and design, man is always taking his cues from nature. The fin, or fins, on the bottom of a surfboard are no exception. Guys like Stan Pleskunas and his long time friend Chuck Ames know that if you want to go like a dolphin, you'll need the right appendages to do so.
Chuck's the proprietor of True Ames Fins (www.trueames.com) and has been cranking out hundreds of different foils for over thirty years. Collaboration with Pleskunas is nothing new and never anything less than exciting. After the sun sets over the lagoon and a good dinner, conversation turns to the more magical elements of surfboard design. Tonight, in particular, we want to better understand flexibility in surfboard fins. This is no easy task. A case of Tecate helps us on our way.
There's no question surfing is at a major crossroads today. It seems the whole world is in a surf frenzy, pushing both good and bad elements of the reality into the forefront of activity. All forms of media are on board, inspiring hoards of new riders to pack old spots. Controversial advances in surfboard production are taking hold to meet new demand for inexpensive wave riding vehicles. At the same time, new materials are being cooked in the lab, while old shapes and styles of riding are being rebirthed. Not surprisingly, flexibility in surfboards and surfboard fins is being examined more closely than ever. And, whereas many feel we've reached a point of tri-fin sta
gnation, there are those like Stan and Chuck who've lived through and were deeply inspired by the short board revolution three decades ago, so much so they continue to innovate into the new millennium. Their world of surf is filled with endless possibilities, many of them crafted in flex.

GEORGE'S WORLD

For these guys, the concept and implementation of flexibility is nothing new. Much of it goes back to the 1960's and George Greenough. In fact, it's impossible to have a discussion of fin flex without bringing up George and his contributions to the sport. "The first time I heard about flexibility, where it really hit me, was in reading about George surfing Honolua Bay on flexible boards," says Stan. The story goes that Greenough's super flexible kneeboard (named "Velo") and it's deep 11 inch fin not only allowed him to visit newfound territory on the wave face, it loaded him up with tons of energy, releasable whenever and wherever George wanted it, especially in the turns. In his understated way, Greenough referred to that catapulting action as "squirt". The illusive "squirt" is what surfers still seek today via a variety of methods. And certain degrees of flexibility in fins are often looked at as the fountainhead of power.
Greenough's design evolution eventually led to the Stage 4, a high aspect fin with a slight amount of flex at the tip. With George's blessing, Chuck makes a couple of versions of this foil. "We've changed it subtly and we've added a bit more base to make it more user friendly," says Chuck. "The Stage 4 was a pretty extreme fin, very performance oriented. It's not a beginner fin. But to a really good surfer on the right board, it's an incredible foil." The "right board" is a subjective matter, but they work best on round boards.
What thrills Chuck is the fact that with faint changes, Greenough's concept can be applied to several different types of surfboards. He goes on to explain how a quiver mentality towards fins is becoming more and more common these days. "So many people have so many different surfboards. Guys are into different boards for different conditions, styles and feel and they want fins for the same reason," Chuck states. "Sharp guys will try three or four different fins before they decide on which one works best."

HANDS ON SURFING

It's important to remember that fins do not operate independently of the board and rider. Several elements work at once to produce good or poor results. Stan explains: "From my experience riding fins and from talking with George, I found when you had a flexible board it was absolutely critical to have the fin exactly tuned, because if the fin over-flexed the board, the board would stop. If the fin didn't flex the board enough, the board would stop."
Stan reaches for the analogy of an automobile. "Just like a car, the performance of a surfboard is determined to some degree by its suspension, or flexibility," says Stan. "The magic flex can be so subtle that it is barely noticeable or it could be as apparent as what Greenough's boards have. With a car you could have the best suspension ever but if your shocks are shot the reduction in performance will be staring you right in the face. Everything has to work together. The big difference between cars and surfboards is the fact that it is difficult if not impossible to quantify the correct flex in your fins, board, or combination of the two. There's so many factors involved."
So, without quantification, what's left us? Well, you do what Stan and Chuck and hundreds of other vanguards in the world of surfing do: You experiment. Trial and error, trial and error, trial and error. Back in the day, Stan's solution was to start with puttin
g on the fins on thick and heavy. Then, as he puts it, "I'd just keep grinding on it and grinding on it, make it smaller. I'd adjust the area and I'd adjust the flex, until I got the board to work. It usually took a matter of weeks. I'd be filing and sanding my fins on the beach. I had a little four-in-hand file... it was round on one side and flat on the other. I'd go down to the beach and I'd rasp it off and foil it down to get it where I wanted it. Then I'd use the bastard file, and then I'd sand it off to get the scratches out. It was an ongoing thing."
This type of interaction with your equipment is critical to not only improving your surfing, but to really understand what is going on with your board and fins. Stan remembers what works best. "I think we need to give a lot more attention to detail and refining what we have, particularly with fins. Think of where we would be if every fin on every surfboard that was made since tri fins became popular was touched with a four-in-hand file and a piece of 400-grit sandpaper on the beach. We'd know a hell of a lot more about what we're doing. Nowadays people throw a plastic fin in their board, go out and break it, put another one in, go out and break it... they aren't really thinking about what's going on under their board."
As for what exactly is going on under the board, it's hard to quantify. There are many knowns but twice as many unknowns. "The very nature of flex is something I don't believe will ever be quantified," says Stan. "It's impossible to produce the same situation over and over again in surfing. Every wave is different, every surfer is different, every board is different. I think at best you're going to get a general guideline for fins. It's not going to be true quantification. That doesn't mean we can overlook flex...it's an absolutely critical function."
Chuck sees a role for the foil shaper in all of this. "You tell the fin maker your specification... it's his job to tune your fins to your thing. If you're 325 lbs., you might need a pretty wide, pretty stiff fin, relatively, because you can make that fin work based on your ability and load. If you're a beginner weighing in at 120 lbs., you would do something else."

 

FOILS 101

A non-surf oriented magazine once asked Kelly Slater how he would describe the feel of surfing to someone who'd never ridden a board before. Without pause, he said, "It's like flying". And it is, which is probably why aerodynamic terminology barges in every time someone wants to talk fins. In short, a fin is a wing. Fins give us direction and lift. Thankfully, science can help explain some of the things going on under your board when you bank that blistering bottom turn.
Stan offers me a fundamental aspect of foils, or wings: "The maximum thickness of the fin at any given point on the fin is a ratio of the cord length of the fin. The cord length is the distance from the leading edge to the trailing edge, parallel to the bottom of the board. If you look at the outline of a fin, the thickness flow should be relative to the outline. Lets say you have a fin that is absolutely rectangular. If you look at that fin head on, it's got no foil, from base to tip. But if you cut out a more typical fin... if you now have a real sweeping, narrow tip and a long base, it should have a correspondingly thick base leading to a thin tip. The ratio is constant through the fin." So the fin gets thinner as proceeds toward the tip, if the cord length declines toward the tip. Stan is quick to point out there are exceptions to this rule. At this point, we open up a bottle of Bacardi.
What should the thickness be? It turns out this is another topic open for debate and conjecture, but a good basic number to think about is 10%. At any point that you measure the fin at its maximum thickness, it should be about 10% of the length of the cord. For an extreme but easy to follow example: If your cord is 10 inches, say, at the base, the maximum thickness of your fin is going to be 1 inch, along that parallel to the bottom of your board. If your cord length is 1 inch, say, at the tip, then the maximum thickness is going to be a tenth of an inch.
Why is it important to understand this ratio or that percentage? Because it gives you a platform from which to understand flexibility, provided you use a homogeneous material throughout the whole body of the fin. It demonstrates that you can adjust the flex of the fin by the template and by the thickness. If you understand and stay absolutely true to your 10% thickness to cord ratio, you can adjust the flex in the fin by simply adjusting the outline of t
he fin.
Where it gets interesting is when you start "screwing around with the thick point on the fin," as Stan puts it. "More or less, it should be around the third point of the fin, and that goes all the way through the whole fin. If you look at a foiled fin you can see where the tips of the glass end, you can see the layers... it looks like a topographical map. A foiler will look at those lines and it will tell him if he's doing a good job. You can measure the tip of that and then take a line parallel to the bottom of your board, across your fin, and look and see if it is just about at the third point."
And now, one of surfing's many trade-offs: "As the thickest point of the fin moves forward [toward the leading edge], you get a wider groove, you get more feeling out of the fin," says Stan. "It's more easy to know, to anticipate when it's going to spin out. And you usually get a little more drive out of it. The problem is you also usually get more drag. If you put the foil way back and you thin it out, say to eight or six percent, now you've got something that goes really fast, but when it spins out, it's gone, and you don't have a chance to recover."
Chuck notes that Greg Liddle really advanced this type of fin. "Greg had these surface piercing fins. He liked the aft part of the foil back at 35% to 37%, and had really sharp leading edges, which at the time was kind of counter to where George's feeling was. He had some of the fastest boards of the era, with tons of power."

MATERIAL WORLD

Aside from the structural rules that apply to fin manufacturing, materials, and how you use those materials, play just as vital a role when it comes to flexibility. Fiberglass, just one of many different materials used to make fins, is a woven product. At what angle fiberglass is applied affects the flex. Chuck flatly states, "Weave orientation is everything when it comes to proper flex."
Glass weave is at a 0/90 bias, which means it is 90 degrees offset from itself. By using weave orientation, a fin shaper can affect the flex of a fin. The weave is like the grain of wood on a two by four. A two by four is strong lengthwise because the grain runs vertical along the board. If two by fours were made with the grain running horizontal, they would easily break in half. They would have no linear strength and be rendered useless.
In fin manufacturing, the same concept is addressed. If a fin shaper orients a fin on a sheet of fiberglass with the grain going with the rake of the fin, it will be as stiff as possible. If he goes with a 45 degree orientation, the result is the most flex possible. If the orientation is changed only 20 degrees, incremental flex is added.
Stan points out that flex isn't just about bending a fin from one side to another. It's also about twist. As far back as 1969, he was attempting to make fins with twist, influenced by Terry Hendrix in San Diego. "I would make a panel where I had 4 ounce [bi-directional glass] for the inner layers," says Stan. "Then I'd put unidirectional glass up on either side of that, them some layers of 6 ounce, then some layers of 8 ounce, then some layers of 10 ounce. When I foiled it off and tapered the fin, I knew I had this gradient of material. The thing would get stiffer and stiffer and I could use less and less cloth. I was left with 4 ounce at the tip... very flexible... it could twist without cracking. On the sides, up in the top third of the fin, the thing that was carrying the load was the unidirectional cloth, running away from the leading edge... so I could get stiffness there without sacrificing flex because there were no fibers running horizontally."
Eventually, what Stan refers to as "a black art" creeps into our conversation. Plastic fins are commonplace today. A perfect plastic fin is much less common. "The problem's in the process and cutting corners," says Stan. "It's an injection mold. The plastic is heated up to liquid and squeezed in there under pressure, then cooled. Well, it takes a lot less pressure and lot less plastic if you really heat it up a lot. The problem is that after you take it out of the mold, you get what they call "sink". The plastic shrinks and you may get a wobbly, bumpy product. And it shrinks the most at the thickest part of the fin. It takes somebody with experience and somebody to watch it to know what's going on."
Speaking of the industry, Chuck adds, "Nobody's saying that we have perfect plastic fins. If they do, then they're selling snake oil. A lot of plastic fins are really bad foils, even when manufacturers have the opportunity to make a perfect one, because they cycle the molds too fast. It's really sad, to me. But the best surfers in the world still have access to the best fins in the world."
And the molded environment isn't a total mess. Chuck has been working for almost two years with RTM (Resin Transfer Molding), a technology that results in no sink after it comes out of the mold. There's no sink because there's no plastic. The ingredients being baked are resin and fiberglass, just like traditional fins. The difference is that with RTM you have a greater glass to resin ratio (by weight). And more glass means more strength. A skilled craftsman performing an old hand lay-up can get the ratio to about 50-50, and most fins are actually 40-60. RTM allows him to drive it up to 70-30, and keeps the fin from fatiguing. If you add fiber orientation technique to this process, you've got a brand new breed of fin, flexible where you want it to be flexible, yet more durable than ever.
This technology is being implemented by Chuck on a strange looking fin
originally designed by George Greenough, dubbed the Stage 6. It's a paddle fin, and, hitting on the same themes that Stan monkeyed with in the late 1960's. This fin's magic is also based on twist. Born from George's windsurfing experience, the paddle has a large amount of area removed near the base. This reduces drag and creates a leg extending down to a filled out "active" paddle, which twists similar to the way a fish flaps its tail. Supported by a leg with a surface piercing foil, the blade (which has a flatter foil) stores up energy in the turns and then releases, providing the sought-after squirt that George found so long ago.
"People are really curious about these," says Chuck, "and of course there's a lot more we can do. They'll have to be patient and experiment. It would be good to see everyone get back on the beach with a four-in-hand file and make things work. There's potential for application for the thruster in this design, and I really believe that this can be applied to make surfboards work better."

 

BACK TO THE FUTURE

Stan's work spans many worlds, most of them aquatic. Earlier in the day, I followed the on again off again whine of a grinder through the back of Stan's workshop. I came around the corner to see Chuck Ames doing what he does best. The sun was setting over the Elkhorn Lagoon and here was the master fin shaper, with the side door to the shop open, letting in all that late afternoon light, sanding away at a futuristic looking fin for none other than Laird Hamilton. In the front of the shop was a hydrofoil to which the fin, or wing, would be attached. It was a strange moment. I expected something different... maybe a laser guided sanding box, vented, with video and computer feedback. But nope, there was Chuck, in t-shirt and jeans, lanky, leaning over a milky jade green fin, kicking up the sander and rubbing lightly down on the blade, a vee-shaped thing which lo
oked like the back end of a Beachcraft Bonanza, turned upside down. He released his trigger finger and let the spinning disk rub away at the foil, shaping it... all by eye, all by hand, all by feel... all by decades upon decades of experience. The wing is going to help Laird from killing himself, and flex plays a critical role.
Again, Stan and Chuck are in the midst of trial and error. The wing will be attached to the back of the foil structure, to help stabilize the ride, and the strut [the big metal blade extending down from the surfboard] is what "makes the thing have yaw stability, like a fin," says Stan. In short, it helps Laird stay on course.
"The problem is, when the thing gets up out of the water you have less and less "fin" in the water," says Stan. "It looks to me like they get twitchy when that happens, as there is virtually no fin area below the strut. The vee shaped tail we're putting on that thing is meant to address the yaw ins
tability inherent on the existing design. Another problem with the foil is that the strut is in front of the center of effort of the foil with respect to yaw motion. This is like driving a forklift at 100 mph with the steering wheels in the back... very scary and twitchy."
"The vee tail Chuck is shaping moves the fin area behind the center of effort and hopefully will calm the thing down and make it behave more like a surfboard," says Stan. "Imagine if all your fins were six inches in front of your back foot. That would be difficult to ride... although not impossible."
Ultimately, this is a test and the proof will be in what Laird and tow partner Dave Kalama have to say about it. Stan reminds me that, "...when looking at the existing foils which, by the way are very well designed for their purpose, you need to understand that they are made for a much more controlled ride. These things are designed to be towed by a boat. That gives the rider another point of reference and increases the stability in all dimensions, thanks to the tow rope. The rider can tell the driver to go faster or slower to adjust for the weight of the rider and the amount of lift generated by the speed of the foil. These things make for a very predictable ride while it is being towed."
"However, when surfing with one of these foils the speed changes radically and the loss of the tow point creates an instability," says Stan. "There are a bunch of issues that need to be addressed to eliminate the need for boots and increase the stability and efficiency of the foil. It's not very often that you get the opportunity to apply lessons learned in aero and hydro dynamics to such a cool thing. I've got to hand it to Dave Kalama and Laird and the guys who make it work by virtue of shear athletic ability. Hopefully the nerds and the athletes will be able to arrive at a design that will open this sport up to the average humans of the world."
And as for flex? "Flex is a factor that as not been even partially explored and the value of tuned flex will be an absolutely crucial factor in getting these thing to work better. The foil we have now is stiff but we'll grind more and more flex into it as we get feedback from the riders."
Stan is bullish on the future of hydrofoils. "The analogy of the state of the foil art is similar to the first guys that surfed outriggers and then someone cut a Koa log into a board and surfing in its present state was invented," says Stan. "These existing foils are the outriggers of our time and with what is known about how foils work the curve on improvements will probably go vertical in the next few years."

MAGIC MAN
My head has a nice spin to it, and I'm not sure if it's because of the Tecate or techno-magic subject matter that Stan and Chuck have been good heartedly walking me through. After decades of thinking about flex, Stan seems a bit more at ease with the complexity of the matter but readily acknowledges its inherent illusiveness.
"It's like doing surgery on a living creature," says Stan. "The board and fin are in a constant state of change with respect to flexibility. Add to that the fact that as composite structures cycle through thousands of bends, they tend to get softer. My gut feeling is the "magic" in the "magic board" is to a very large extent "the flex". So it seems that thinking about tuning the board, the fin, the whole system throughout the life of the board to keep that magic alive makes sense."
At this point, the soul of surfing peaks through the fray. "Flexibility is invisible and transient. Yet it's very important. If magic were visible we would know how to put it in every single board, but it's not. In the end, I'm not so sure I would dig it, if all that stuff was quantified, packaged, and sold."
The Tecate is exhausted and I step out for some fresh Monterey Bay air. Down the hill, the Midnight Special hoots her horn and clacks by. As the train leaves the slough, another auditory sensation greets me. I call back in the house, "Hey Stan, can you hear the ocean from here?"
"When it's big, yeah."
"It's big."
The next morning at Scott's Creek I find out first hand what flexibility is all about, not only with my board and fins, but with my hung-over body as well. The first big swell of the season is upon us, and with each drop I can't shake the image of my fins loading and releasing down in the brine.

GO YOUR OWN WAY!

What does flexibility mean to surfing? Or, more importantly, what does flexibility mean to your surfing? Ultimately it’s you on the wave, on your wave vehicle of choice, on your fin or fins of choice. Could there be anything more personal? Could there be anything more complex? Could the problem be any more beautiful? Experience the trade-offs, know what happens when you glass too thick or sand too thin. Just like Chuck Ames in Stan's shop, grinding away at the foils of the future, or just like Stan back in his San Diego days, you should be on the beach, filing away at your fins, trying different set-ups, always tuning, all in an effort to stay in tune with your surfing.
In an era of cheap, mass-produced boards and warbled plastic fins, surfing's individuality is on the gurney and the pulse is dropping. Don't worry about the patient. He's going to die. Your job is to move on, discover, think and do.
To seek flex is a personal journey to discover untapped power sources. It's still about wave riding, but it's your choice how deep you want that experience to be. In the metaphysics of surfing, you'll always get back what you put into it, and more.
Think about it, and think about it again. What would George do? George would go surfing! George would take it into the beach, get on his hands and knees and sand that fin. Sand, spit, sand, eyeballing, feeling. Then right back out again, seeking the infinite feedback loop.
"In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual." - Galileo
Flex means power by a matter of degrees. Go find out for yourself!

 

thanks, clemson. i've had this article saved on my computer for so long i'd forgotten where i initially got it.

 

did you even read the article? do you know anything about chuck ames, his company, or the fins they make? "coolest art". jesus, but you're a special kind of stupid. you probably still think that the plastic fins that come w/ a board off the rack work great.

 

untrue. can't believe everything you hear.

 

you know exactly what i meant when i said "plastic". stop being disingenuous.

just b/c someone has something to sell doesn't mean that their knowledge should be discarded w/out thought or consideration. simon anderson was already an established shaper when he created the thruster, so he clearly had something to sell. should we have rejected that as well? i really don't get why people are so averse to accepting the idea that the fins on the bottom of their board matter as much as any other aspect of the design.

 

your "source"? who's that? roy?

 

if i needed further proof that you're full o' crap...