Why are fins important in surfboards?
Surfboard fins are crucial in a surfer’s ability to change direction, maintain/increase speed, and control while riding a wave.
One key function of fins is energy transfer: changing gravity and wave energy direction so the surfer can travel across the wave.
Gravity should be easy enough to understand, but it somehow feels a little different because of the ocean. Nevertheless, gravity pulls the surfer to the bottom once a surfer stands on a wave.
At the same time, as a wave breaks, the water under the surfboard moves upwards in a circular motion, pushing the surfer upward.
The fins are positioned at the right angle to those vertical forces, creating grip and helping the surfer stay in place and travel across the wave.
Fins also work as a pivot. When a surfer attempts to turn, fins work as a pivoting point so a surfer can turn the board in a controlled manner. In the case of a thruster, it provides extra leverage for the turn.
Side fins have an extra function.
Side Fins, in particular, one side curved and the other flat. The curved surface faces outwards or towards the wave. This is to create ‘lift’, and it causes fins and surfboard to travel towards the wave, helping to fight gravity.
This is the same concept as how aeroplane wings help the plane to fly. The curved surface area creates low pressure, making the wings travel upwards.
The surfing fins cause fins to travel sideways, helping to stick to the wave or prevent going to the bottom of the wave.
Fins also prevent sliding out and help control the board.
Sliding out refers to the motion of the surfboard going in a circle on the top of the water’s surface. Imagine an inflatable tube on top of the water without anyone in it. It’s easy to spin this with minimal effort.
The surfboard is the same without fins. It will move either way easily. Having fins increases resistance to this rotation significantly, making it more predictable when a force is applied in either direction.
Different Fin Set-Ups
Fin set-up refers to how the fins are put on the board. Each board are manufactured with a certain fin configuration in mind, and you cannot change it once it’s produced.
To make the surfboard more versatile, many leading surfboard manufacturers make 5-fin set-ups now, so the surfer has some options to play with.
Here is a summary of different types of fin configurations. Read on for a more detailed description.
| Types of Fins | Pros | Cons | Surfboard |
| Single Fin | Good control and hold. Increased height prevents sliding out during noseride. | Increases drag. Difficult to turn. | Longboard. Retro surfboard – Mid-length |
| 2+1 (Single fin with side bites) | Compared to a single fin, make the board looser. | Increase drag. Not suitable for noseride. | Longboard. Retro surfboard – Mid Length. |
| Twin Fin | Fast speed due to less drag when on a rail. | Less control during turning | Fish Surfboard |
| Twin Fin with trailer | Improve control compared to twin fin alone | Increase drag compared to twin fin. | Fish Surfboard |
| Thruster | Well balanced between control and speed. | It is slow compared to Twin Fin or Quad | Shortboards and mid-length |
| Quad | Increase speed when on the rail. | It is stiffer compared to thrusters | Shortboard and mid-length. |
| Quad with trailer (Knubster) | Add more control than quad | Adding drag and weight. | Shortboards. |
Single Fin
The single fin sits in the middle and has a broader base and height. It is predominately used for longboard and retro types of board. Single fin has a unique fin box, allowing position change of the fin.
Because of its long base and the height of the fin, it makes the board quite stiff. However, large single fins are essential for nose riding. When a surfer stands on the nose, it can tilt the board forward. A long single fin ensures the fins are always submerged, preventing sliding out.
Also, its wide base helps stabilise the board when a surfer walks up and down the wave. If you want to read more about what makes a nose ride longboard and nose ridding technique, read here.
2+1
This is a popular set-up in performance longboards. There is a large single fin with one small side fin on each side. These side fins are often called side bites.
The purpose of this setup is to make the board slightly looser and make it easier to turn. Single fin used in 2+1 is often smaller than usual longboard single fins.
Twin Fins
Twin fins usually come as standard for fish surfboards. Twin fins are great for speed, as the centre fin causes the main drag. Twin fins have longer bases and rake, which make the board stiffer and provide hold.
This type of fin is great for small waves.
Twin + trailer
Twin-fin surfboards sometimes come with a centre fin box, allowing the option for an extra centre fin. The centre fin between twin fins is smaller to minimise drag than the standard centre fin. An extra centre fin will make the board looser, allowing easier turns.
Thruster
The thruster set-up has three equal-sized fins, allowing well-balanced between speed and turns. It has more holding power than twin fins and is more loose than single fins. The name thruster was given because it gives ‘thrust’ when coming out of turn.
Thrusters generally have more drag because the angles of the side and centre fins differ.
Quads
Quads are set up like twin fins but with slightly smaller fins behind each side fins. Fins on each side are at a similar angle. When the board is on the rail, there is less drag than the thruster, helping to gain more speed.
However, when the waves are not steep enough, all four fins will be submerged. These will create more drag.
Turning on the quads will be stiffer compared to the thruster.
Quads with trailer (Nubster)
11-time world champion Kelly Slater used this set-up during competition. Nubster is a tiny fin slotted in the centre fin box, and Kelly Slater claims this little friend can give the “stability we wanted from quad”.
Dimension and template of the fins
Fin Base
Fin Base is the horizontal distance in contact with the surfboard. Turning becomes harder with a longer base because it adds more water surface to push against. Think of it like opening your hand versus making a fist in water. A bigger base means more resistance, making the surfboard stiff.
Fin Rake
The rake is like the fin’s backward tilt towards the board’s tail. If you increase the rake, the board becomes stiffer when applying the same force. The rake and fin base usually go together – the longer the base, the more the fin leans backward.
Fins Height/Depth
Fin Height or Depth is the vertical distance from the base of the fin to the tip of the fin.
The height of the fins determines how much resistance you will have when tilting the board from one rail to another. As you tilt the board from one side to another, you can imagine the fins working as a barrier to this tilt.
Therefore, bigger fins mean more resistance to turning and changing direction. But, if you get fins that are too small, they do not have enough surface area to stabilise.
Longboard centre fins are almost always quite big. There are several reasons for this size: to help the surfer nose ride and to avoid sliding out when you are standing in the front part of the wave. If you want to learn more about longboard surfing, read here.
Then, the most important question: Is it worth spending money on the fins?
Toe-in angle
This is about how the fins are positioned compared to the stringer (the central part) of the board. Increasing the toe-in angle means the side fins point more towards the nose of the board. A higher toe angle helps with turning. However, having too much toe angle slows the board down due to resistance/drag.
Cant Angle
The cant angle refers to how much the side fins are tilted compared to the bottom of the board. Centre fins are usually straight at 90 degrees to the bottom, while side fins tilt outward. Cant angle helps the board stay on the wave and offers extra support during turns by increasing surface area.
More cant angle also helps to tilt the board rail to rail.
Interestingly, FCS has a fixed cant angle in the fin box, whereas Future has the cant angle set within the fins.
Foil
Foil refers to how fins change in thickness. They begin narrow at the front, get thicker, and then taper towards the tail, creating a sharp edge at the back. This design aims to enhance the speed of a surfboard.
The narrowing at the back allows water to flow smoothly, reducing resistance. If fins are blunt at the back, it can create turbulence and more resistance.
Top fin makers have worked on perfecting foil shapes to minimize drag, ultimately boosting the surfer’s speed.
Can You Surf Without Fins?
Suring without fins is possible; some surfboards are designed explicitly for finless surfing. In fact, the very first surfboard, called Alaia, did not have fins, and it was made of a single piece of timer.
Once on a finless surfboard wave, as the water passes under the surfboard, it goes around its rail, creating some grip. This keeps the surfer on the wave.
Without fins, there is very little force stopping the board from sliding. Therefore, it tends to spin. Experienced surfers, however, can use this and perform maneuvers on the wave. See here for an example.
Turning on finless surfboards is difficult, but it’s possible. As you can see above, the surfers can change the board’s direction to go up and down the wave. However, any critical turns are not easy.
