Thrusters and Quads - A Guide to Surf Fin Setups
How to Choose Your Fin Setup
A Brief History of Fins on Surfboards
Owning a surf shop means spending a lot your time talking about surfboards, and one topic that people ask me about practically every day is the difference between three fins and four fins on a board. To truly understand the difference, it is important to first understand the history of fins in surfboard design, and how they evolved over time.
Surf fin from the 1940’s on a Hawaiian wood paipo surfboard Photo: usvsa.com
The original surfboards didn’t have fins. Hawaiian designs such as olos and alaias were ridden either straight, with a side-slipping motion, or by using the foot as a rudder to help turn them. It was only after Tom Blake added the first skeg to a surfboard in 1935 that fins became a standard part of the surfboard design—and from then through the early 1970s, virtually all surfboards were made with one fin.
1945: Tom Blake attaches an aluminum speedboat keel to the bottom tail of his hollow paddleboard. Photo: Surfing Heritage and Culture Center
These “single fin” boards featured a large, deep fin set along the stringer in the center of the board, back near the tail. Single fins were stable and predictable, but slow and simple. Turns on these boards had to be gradual in order to keep them from spinning out, and the large fin in the center of the boards’ planing surface caused a ton of drag, which reduced speed.
In the 1970s, the twin fin became popular, particularly in small waves and on shorter boards such as the fish. Two fins, set out near the rails of the board, created thrust as the water was funneled between them, making for a much faster ride—but also one that was less stable and more “skatey.” This worked great in small, soft waves, as well as lined-up point breaks, but was not ideal for larger, more powerful waves, where the stability of a single fin allowed guns and mini-guns to fit into the hollower, more powerful pocked.
In 1981, Simon Anderson unveiled the thruster design in maxing, triple-overhead surf at the Bells Beach contest. Combining the two side fins featured on a twin fin with a stabilizing fin in the center that was much smaller than most single fins, the thruster was the best of both worlds. While it didn’t generate as much speed as a twin fin, due to the drag created by the center fin, it still had much of the thrust of a twin, making it much faster than a single fin. At the same time, the stabilizer in the middle solved the overly loose issue with twins, providing much-needed control in the pocket, while the fact that the fins in the cluster were smaller than the typical single fin made the board much easier to maneuver.
Around 2010, a handful of pro surfers, including CJ Hobgood and Kelly Slater, started surfing quads in contests. Quads had actually been around since the late 1970s, but had fallen by the wayside due to the popularity and proven utility of the thruster. But the success that Hobgood and Slater had on quads got the general public thinking outside the box once again, and eventually the quad began to enjoy a resurgence in popularity. The design principles surrounding quads and their placement were refined, which meant that the modern quads performed a lot better than the ones in the 1970s. And while thrusters are still the most commonly used design on high-performance surfboards, quads have become commonplace, both on shortboards, barrel boards, and big wave guns. In fact, most shortboards now come with five fin boxes so that surfers have the option to switch between thrusters and quads.
The Best of Both Worlds
If the thruster was a compromise between the twin fin and the single fin, then the modern quad is a compromise between the twin fin and the thruster. Like the twin fin, a quad enjoys increased speed due to the thrust and drive of water being funneled between the fins on each side of the board, with no center fin to create drag and slow the board down. However, the trailing fins on quads, which are set a few inches back and around an inch closer to the stringer, serve as a sort of semi-stabilizing force, effectively lengthening the side fin’s influence and bringing a bit more control to the center of the board. Quads are slightly slower than twins but noticeably faster than thrusters. They are also slightly more stable and controllable than twins, but not quite as stable as thrusters.
Pros and Cons of Each
When it comes to small waves, the main difference between thrusters and quads (aside from the speed) lies in the board’s ability to be surfed hard off the bottom, as opposed to more laterally. Thrusters can really dig into the base of a wave, enabling sharp, aggressive changes of direction that allow them to be projected vertically up into the lip. Quads, on the other hand, are more likely to spin out if they are pushed hard off the bottom of the wave. Instead, they do better when they travel in the center of the wave, driving down the line toward the shoulder, and then are finessed into slightly rounder carves. While the best surfers can still take quads through aggressive bottom turn/top turn combinations, they ride best when they are thought of sort of like a “twin fin+.” Lateral projection lends itself to big airs and other maneuvers that traverse large distances, and the two fins set along the rail lock the board into longer, deeper carves when the board is finally put on edge.
When it comes to bigger and hollower waves, the story changes slightly. The emphasis is less on maneuvers and more on riding the barrel and making big sections. Thrusters tend to do a little bit better in slabby waves that require super late drops with abrupt bottom turns, as quads are a little more likely to spin out while bottom turning through critical sections. Thrusters are also easier to control and hold in place when stalling on the backhand, whereas quads are more likely to side-slip during butt-dragging stalls and then fail to regain their line. However, quads have the added speed that makes it easier to come out of barrels. In addition, that fourth fin provides a little bit of extra stability when riding deep on the foam ball.
On big wave boards, the thruster setup tends to handle chop a bit better, which is helpful on huge, windy days, when the board is bouncing its way down the face. However, most big wave surfers now use quads on their guns almost exclusively due to the extra speed, which helps then make it around the huge, long sections that characterize most big wave spots.
The Choice is Yours
Ultimately, it is up to the surfer what they enjoy riding—the stability and more traditional, bottom-to-top maneuverability of a thruster or the speed and skatey feel of a quad. Most people end up riding both, depending on the conditions and what board they are on. And that’s the great thing about modern surfboard design—with removable fin system and five fin boxes on most boards, you are free to experiment as much as you want!