Why Do Surfboards Have Fins?

Why Do Surfboards Have Fins?

Wondering why do surfboards have fins? The surfboard fins are essential in maintaining the speed and direction of a surfboard, as well as a particular grip on the wave. There are different fin shapes, sizes, and configurations that achieve the previously mentioned things in differing ways.


Without the surfboard fins, you could ride the waves like ancient Hawaiian kings did, using rails only. Surfboard fins will provide a sharper surface that increases speed. They also allow the riders to hold the line during increased surfing sessions. You can compare them to snowboards with a sharp edge, rather than a dull edge.


Where are the fins located on the surfboard? You can find them at the bottom of the surfboard. They all feature a curved appearance and come in a variety of shapes and sizes. You can also find fins with different levels of flexibility. It all depends on the needs of the surfer.


Let's find out more about why do surfboards have fins in the following paragraphs!


The Science Behind Surfboard Fins


So, why should you have fins on your surfboard? Well, fins create two things when it comes to surfing science. They create lift and drag. What is the lift in this context? It is the force that helps you turn with the surfboard, and helps with the tracking as it gives you a base to push off from. That's why the fins are designed smaller so that the surfboard can go faster, and the surfer can feel more drive.


What is the drag in this context? It is opposite to the lift. That means that drag slows you down; you can visualize it as a sort of a braking mechanism for a surfboard. There are four types of drag: dynamic drag, form drag, interference drag, and skin-friction drag.


Dynamic drag shows up as a result of surfboard fin moving through the water. Drag and lift progressively increase with speed. When the fin moves through the water, vortices may show up. They cause drag as they rob fins of lift. That happens mostly when you turn your surfboard. The trailing edge of the fin can also create vortices, except the instance in which the trailing edge is sharp like a razor. That isn't the best practice in surfboard design, so striking a nice balance between smooth and sharp is ideal to decrease drag as much as possible.


Form drag is caused by the surfboard fin shape. The things to look out for are the aspect ratio of the fin planform (or template in surf culture), taper ration, and the rake. Fins that have water flowing across the fin chord are faster, with less drag. Those that have water flowing across and on the fin are slower and have more drag. You should also consider the fin thickness and foil section as they also serve their purpose when it comes to drag amount.


Interference drag is caused by the fin connection to the surfboard. The rule of the thumb is, longer connection equals more drag. Shorter fin base can lower the drag levels. But, that is not the only way to lower the interference drag. We can also make a bulbous forward section of the fin, similar to ship bows.


Skin-friction drag slows you down because of the surfboard surface roughness, and of the surface area of any type of fin you have. The rule of the thumb is: the rougher and bigger the fin area, the more drag will be induced. Most people think only about the fin length and height and ignore the area attribute. Even when buying surfboard fins, the fin area won't be specifically listed. Nevertheless, you should definitely look into that as it is the true make or break attribute!


Now that you have an outline of the science behind the surfboard fins, let's find out more about specific components of surfboard fins!


Surfboard Fin Toe


The toe is known as the angle of the fin in relationship with the center stringer of the surfboard. Most side fins are toe-in, which means that the front side of the fin is angled inward to the stringer. These types of side fins cause the water to apply the pressure to the outer sides of the fins. This will make the surfboard more responsive to your actions.


Surfboard Fin Cant

  A surfboard fin can is an angle that it makes in a relationship with the surfboard bottom  

The cant is the angle that it makes in a relationship with the surfboard bottom. A surfboard fin that sticks upright, perfectly vertical to the base contour of the surfboard has no cant. A surfboard with a cant has fins that point outward, toward the rails of the surfboard. When you increase the cant of the surfboard, the board will be more responsive when it comes to turning. Decreasing the cant and bringing it closer to 90 degrees will make the surfboard faster, which will be the most impactful while riding the waves in a straight line.


Surfboard Fin Foil


You can notice that a surfboard is shaped in an aerodynamic way from its front edge to its backside. This shape is known as the surfboard fin foil. This part of the surfboard fin has a huge impact on the way the water flows under the surfboard. There are surfboard fins that are flat on one side and with foiled side fins; and those that are foiled on either side of the surfboard. The point of the foil is to create a space under the surfboard and help thrust it in different wave conditions. When the foil is more noticeable, it will provide a better thrust. This part also slows down the surfboard, which helps with maneuverability.


Surfboard Fin Rake

  Surfboard fin rake calculates how far the fin curves are from the base  

This part of the surfboard fin calculates how far the fin curves are from the base. Surfboard fins with small rakes will thrust the surfboard faster and increase its stability, with a sacrifice in the maneuverability. Fins with large rakes will give the surfboard a better turning radius, with a sacrifice in its stability. You should strike a balance when it comes to rakes to adapt to the different waves you may ride.


Surfboard Fin Flex


The flex of the surfboard fin will play a huge part in the way it handles in the water. Stiff fins are better for beginners, as they offer superior stability. With stiff fins, it is harder to make sharp turns though. On the other hand, flexible fins are slower to reach maximum flex level, which makes the surfboard more difficult to control. This can cause some headaches for new surfers.


We hope that you now have an answer to the question of why do surfboards have fins. They are an important part of the surfboard constructions, a make or break part of sorts.


Here is a bonus video explaining surfboard fins:


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