Tuna Taper

On a midwinter morning in 1964, I watched George Greenough fight a tuna on a light rod right from the beach at Alexandra Headland, in front of the Surf Clubhouse, dripping wet in an early Dive N’ Surf wetsuit.

He hooked up the fish by kicking out on his Hodgman air mat a couple of hundred yards right into the school, which were common along Australia’s east coast in the 1960s. He’d skipped a small strip of mullet across the frenzied pack, with no lead sinker. Sure enough, a hungry tuna hit it up. Fighting it ashore, George had a savage grin, his eyes intent, his nose buckled up in wrinkled delight.

In no time, he landed it, the beautiful animal kicking and thrashing in the little shorebreak as George ran down to it, fishing rod vertical in one hand, grabbing the tuna’s tail with the other. It was about 10 pounds, sleek and shimmering, with its distinctive yellow slash on its rear half.

George had lobbed into Australia a few days earlier to visit his friend Bob Cooper, who was the glasser at Hayden Surfboards, where I was the shaper. Coops didn’t have space for George, as he was living with Hayden and Hayden’s wife, Faye, and little baby, Grant, at the time. So Coops hit us up to house George for a couple of months. You could do that back then. Our pad was down the road a mile at Mooloolaba, a dingy flat under a greasy takeaway shop and movie theater shared by me, gloss coater Russell Hughes, and sander Algy Grud.

Anyway, back to the beach at Alex: George landed the fish, removed the hook, and, as he crouched down on the hard sand, called me in. “Have a go at this template… Perfect high aspect with taper… And the flex… You know these things accelerate at fantastic speed… Like, zero to 35 in two seconds. And look at this taper…” (I was learning that this is how George talks: a constant stream of excited revelations.) He surprised me as he swung the fish around so that we were looking down its spine to the tail, front on. We were shoulder to shoulder.

“See the taper upwards,” he said. It wasn’t a question, but a command. “It starts kinda thick and solid. That’s to get that giant muscle down its side to become its driver. The tail fin is just the end part of the muscle. Just one flex of the muscle and the fish is flying! But then it thins out all the way up. But check this! Right near the tip, it suddenly goes really thin. That’s concave taper. That lets the tip twist and wash out. That means there’s perfect application of the power—no cavitation. Remarkable, Bob. Tuna are amazing. That’s why I put that fin on my Velo. It’s a straight copy of a tuna’s tail.”

Of course! The light went on for me: marine design for our surfboards. Duh! 

“Well, we’ll have to try one on our boards,” I said. “For sure.” 

The last part of the conversation was heard by Algy, who’d joined us. Being our sander, he was quickly off across the road back to Hayden’s factory. Within a few hours, he’d cut the Phil Edwards fin off the board I’d shaped for him a couple of months earlier, cut out a George- drawn white fin panel on the bandsaw, foiled it, and glassed it on the board. It was the first Greenough-inspired fin on a 9-foot surfboard.

I took a different route. I immediately cut the George template out of a slab of marine plywood. I also cut a standard Phil Edwards–in- spired fin and a Dewey Weber–inspired Hatchet fin, and gave them a reasonable foil. I ground the Phil fin off my 9’3″ and routed a slot into which I glassed two panels of ply, leaving a slot in the center, creating a very basic fin box.

The next morning, the wind had shifted southeast, the swell had jacked somewhat, and Russell, George, and I climbed into Algy’s old Chevy and chugged up to Noosa, 45 minutes away. (Amazingly, the only route to Noosa in those days was via Nambour, unless you cut through private property called Diddillibah and opened and closed two gates on a smooth dirt road.) Tea Tree was a pretty average 2 to 3 feet and a bit bumpy—just perfect for testing fins. Algy rode a couple and was frothing about the tuna fin. I plugged the Hatchet in and rode a couple. The tail spun out badly over the sucky rock section and felt generally pretty bad. Too much leverage down deep. The Phil felt better because it at least tapered in area toward the tip, but again it spun out when noseriding across the shallow rocky bit. Finally I plugged the George template in, pushed the noseride over the hollow section, and didn’t spin out! Not only that, the board’s bottom turns and cutbacks were flowing, smooth, and powerful. Easy control. Painfully obvious, the marine design was the only natural way to go.

That night, George gave us the next element required to get the most out of the tuna-inspired fins: a quality fin panel made out of strictly woven glass fabric, not cheap chop-strand fiberglass. Hmmm. We had to convince our boss, Hayden, that this was the way to go, the future of fins. So, while we worked on him, I quickly grabbed a pile of cloth corner offcuts from Cooper’s room and made up a small batch of white resin, then another in black. I hastily laid up a small panel, enough for one fin, on an old car windshield of thick, flat glass. I alternated the layers so, theoretically, they would be super visible, to enhance foiling the fin later.

The very uneven layup resulted in an extremely wonky foil pattern, teaching us we needed a high-quality, well-squeegeed layup with sufficient resin to wet the fabric, but no more. (George had already explained that, but as usual I thought I knew better. Again, George was trumps.) So we listened closely as George educated us about how to foil the fins correctly, showing us how to concave-taper the foil to induce twist and tip washout, just like the tuna itself. Just brilliant! Lessons never to be forgot- ten, only reinforced through usage.

Hayden gave into our experimentation, and our pestering, and approved the first full-cloth fin panel. Expensive, but the way forward for really hot surfing. Yeehaw!

We immediately started fitting George’s fins onto Hayden’s boards, which were being sold through the few retailers in Sydney, among them the truly excellent Bondi store owned by great surfer Robert “Bonzer” Conneeley, who rode and championed our Hayden boards in what was the hottest market in Australia, due to the number of great surfers in the area. Con- sequently, the Hayden brand quickly became the hottest thing in the land. Of course, the fact that Hayden riders were winning so many events along the eastern seaboard certainly helped.

We listened closely as George educated us about how to foil the fins correctly, showing us how to induce twist and tip washout, just like the tuna itself— lessons never to be forgoten.

Conneeley won the Juniors at the World Contest in Manly in ’64, while Russell and I took out lots of Queensland Titles and placed in the Australian Titles in ’65 and ’66. And so on. 

Then Nat Young took out the 1966 World Title in San Diego in absolutely startling form on “Sam,” his self-shaped Involvement-style board armed with, yes, a beautiful fin hand-foiled by George that the two of them had tweaked a week before the event while surfing up at the Ranch. Magnificent! The tuna-inspired fin hit the world consciousness! Goodbye to Hatchets, reverse fins, Phils, and Dorks. It was marine design all the way from then on, globally! Not that everyone got the concave taper and tip washout. But, truly, every fin designed for the market after that carried George and tuna DNA.

*

As the frantic years of the Shortboard Revolution (1967 to 1972) ripped by, we quickly established a couple of very firm principles of surfboard design. One was that getting the fin under your back foot was essential to manage the new power available from these high-planing shortboards. Direct drive. Quick response. One day, the mighty Ted Spencer and I surfed alone at Broken Head, a long, sand-bottom pointbreak. Although the boards that day were roughly inspired by cuttlefish skeletons with quite rolled bottoms—still under the thrall of Greenough’s hull design—we found we could wind up terrific speed if we linked together a long series of turns, always aiming down the line, no cutbacks, building power and speed turn by turn. We had unknowingly tapped into “apparent flow.” (More on that later.) 

Come the late ’70s, George and I and many other Lennox Head surfers were getting crowded out at the Point. After witnessing Scotty O’Connor and Mark Paul tearing up windy, choppy nor’easter surf on shortened Windsurfer-brand boards, we got into shaping hotter and hotter windsurfing sailboards, and that naturally necessitated designing better fins to match the rougher conditions, as well as masts and sails that utilized tip washout, just like the fins.

The thing about windsurfing is you have the sail rig right in your two hands, and the game is all about pointing that rig right into the wind flow in all kinds of subtle angles to achieve the best power extraction for that moment. You just think of a subtle change, and it’s done. Immediate! No other sailing system can match it for that aspect. Instant angle-of-attack adjustments. The sail is a wing. Can you imagine how the yachts in the America’s Cup would envy that direct brain-to-sail adjustment speed? Partly flexible components in aircraft wings is a big area of research, but the reactivity is another story altogether, requiring complex sensors and reactive gearing. Birds, fish, and surfers have it licked.

So often we pored over a dead seagull’s wing and a feather’s taper, or read everything we could about sails, masts, foils, super yachts, sand and ice windsurfers, world sailing speed records, hydrofoils, cavitation, ventilation, tip vortex, vacuum bagging, epoxy and EPS, wood-veneer laminates, and on and on. All this while surfboards were heading through twin- fins via Mark Richards and Reno Abellira, then to Simon Anderson’s brilliant Thruster design. It was an era of design progression again in top gear. It was an expensive addiction, but we learned so much.

One little invention in particular helped us out. While riding on the old Manly hydrofoil ferry in Sydney Harbor, I observed fence-like structures wrapping around the foil legs facing directly into the water flow. Of course, they are actually called “fences,” and they act as barriers to block air from traveling down the leg into the low-pressure (upper) side of the foil itself. Once air filled that cavity, the laminar flow of water over the wing-shaped foil immediately lost its lifting effect. No water on the topside, no lift. That explains so many of our sudden spin-outs at high speed when windsurfing in rough water. Ventilation, like opening a window, allows a cavity to form on the low-pressure, “sucking” side of the fin: cavitation. You’re flying along the choppy ocean outside the surf, gaining high speed to drive into your jibe, when suddenly the whole tail goes into a slide. The fins explode out of the water, and all your speed is lost. That’s the curse of high-speed rough-water planing. 

On returning to Lennox from Sydney, I made small fences and glued them onto my fin, just like on the big hydrofoil boats. Voilà! The end of ventilation, and much of its big brother, cavitation.

I took the design to my friend John Thomas, who owned the company Multi-Fins, and he reproduced it in molded polycarbonate. He took it to the big European trade shows and sold a hundred thousand or so. He paid me a small royalty, which helped feed our tribe of five kids. 

But another form of cavitation remained.

*

Fish breathe oxygen suspended in water. Champagne releases natural carbon dioxide for hours after you pop the top. Your standard can of beer does the same. Your Coca-Cola has carbon dioxide pumped into it. Your local surf break has heaps of oxygen, nitrogen, argon, and even just plain old air mixed into the water from simple agitation. Waves breaking pull air into the water, and some of it stays suspended for a while. Same with ocean surface water, especially when it’s windy and choppy. 

So what? Those gasses love low pressure, so they can emerge and gather together and form a bubble on the low-pressure side of your fin, again ruining laminar flow—that is, letting the water go from flowing around both sides of the fin to just the high-pressure side. That’s the end of your lift. Lift is necessary in windsurfing to counter the winds forcing you sideways. Lift is necessary in surfing to counter gravity pulling you down the wave’s face. Really, surfing is just taking the energy of the wave’s forward motion, combining that with gravity’s downward pull, and then interplaying it with the upward lift of the surfboard—its hull, its edges, and particularly its fins.

Partly flexible components in aircraft wings is a big area of research, but the reactivity is another story, requiring complex sensors and reactive gearing. Birds, fish, and surfers have it licked.

How does this gassing form of ventilation affect your surfing? First, by fin spin-out (most glaringly experienced when noseriding). Second, by ruining your pumping speed-runs across a fast wall. Third, by feeding your tip vortex and sapping energy. 

What’s the solution to gassing and cavitation? Tip washout. You ever see a stream of bubbles off a big fish as it accelerates? Nup. Its tail fin has flexible ends that keep the laminar flow intact. Flexible fin tips and wing tips have tip washout, just like a tuna’s got, or a good sail, or a good surfboard fin. 

In 1970, Native Hawaiian surfer Joe Kitchens took me for a spin around the Islands in his Cessna. (What a gift! Thank you, Joe!) It was a never-to-be-forgotten experience, from Honolulu up over the incredible Kauai pali to Niihau, where Joe had surfed several spots reserved for full-bloods, back down to Molokai’s big right- hander in front of the leper colony, where he’d surfed as well, then back into Honolulu. As he checked in with the tower, he was told he had to circle for five minutes because a big 747 had just landed. 

“So what?” I asked. 

“If we go in now, we’ll be pancaked into the tarmac, or else jacked into space by the Boeing’s tip vortex.” 

“What?” I quizzed.

He explained that big wings produce a huge spiral of spinning air off each wing tip, be- cause high-pressure air under the wing is always trying to spill over the wing tip to fill the huge low-pressure zone on the upper wing, which is the force that keeps a plane airborne. But, as the plane keeps moving forward, the high pressure never quite makes it around. Instead, it just creates this giant spiral that saps some of the plane’s lifting force, consuming more fuel in the process. 

Since 1988, Boeing, Airbus, and many others have installed various forms of winglets, those little upsweeps on the wing tips. They act like fences, blocking the high pressure from spilling over into the low-pressure topside, drastically reducing tip vortex. When they were installed, they instantly saved more than 5 percent of jet fuel through greater efficiency. 

But here’s the rub: In recent years, wing designers have had a new tool to play with. Because the main spar, or beam of the wing, is now made of composites—basically fiberglass, carbon fiber, and resin—they have the magic ingredient of flex! Yes, they can be designed to let the tip flex directly into the angle of attack, which encourages the maintenance of a very strong laminar flow right around the tip. That “sealed-off” tip section of perfect laminar flow is a sufficient-enough barrier to block out tip vortex. Brilliant!

But George showed us that in 1964. He took it from a fish. 

Boeing and Airbus have dropped the wing- lets on the designs to be released in 2024 and 2025. They’re using twist instead. More efficient. And they’re really just getting started.

Surfboard fins need tip flex and twist to eliminate tip vortex, drag, and cavitation. This kind of flex, as achieved through careful foiling, follows proven flex patterns that include a fea- ture called concave taper. This kind of foiling keeps the base and stem rigid while encouraging the tip to twist into the water flow at all times. Tip washout. Perfect laminar flow. 

Finally, to sand sailers, ice boats, and windsurfers: They use the wind so efficiently that they can travel at amazing speeds. The current world record is 225 kilometers an hour (approximately 140 miles an hour)! That’s seriously dangerous, flying along over hard-packed sand in a flimsy vehicle. Glenn Ashby achieved this speed in just 40-odd kph (about 25 mph) of wind. 

How is that possible? Because, like stick- ing your hand out the car window, forward motion creates its own wind. As that wind adds to the natural wind, it compounds, and a clever sailor keeps resetting the sail’s angle of attack to gain more lift, compounding the sail’s lift redirected as speed, and so on—truly an amazing combination of physical forces. Really, the faster you go, the faster you can go. 

Similarly, your surfboard fins are just little sails, functioning in a fluid 800 times thicker than air. Hence, you only require fins 800 times smaller than a sail to develop forces powerful enough to propel a human very fast on a wave. And the equivalent to a land sailor utilizing apparent wind? Good arcing turns, as well as pumping. 

I was recently sitting on the rocks at a little-known pointbreak, watching Bryce Young getting barreled amazingly, and then, on the soft 6-foot shoulder, pulling these beautiful swooping, dropping arcs around whitewater, projecting so fast out onto the face, just like 1970s down-the-line point surfing. It all made sense. Those arcing turns take the wave’s forward power and progressively multiply the angle of attack using apparent water flow, building speed exponentially. And pumping? Each time the surfer pumps, he actually decreases the angle of attack by “lightening” himself momentarily, then increasing the angle of the water’s attack as he pushes down. The water striking his fins is tighter than ever, and his board is faster than ever. All the more need for well-designed fins with tip twist or washout. 

So, just as George taught us on the beach at Alex that winter morning in 1964, the tuna’s tail fin has all the principles of efficient fluid flow simply built in. Us humans have just got to analyze those principles and apply them to our current and future craft in the water and air—a wonderful occupation for the sons and daughters of the human race.

[Illustrations by Daniele Castellano]