How to choose fins
Choosing the right fins to optimize the performance of your board depends mainly on three variables; fin support or box, board size and you.
Below is a simple guide to help you choose the right fins.
Fixed and interchangeable fins
Fixed keels or Glass-on fins are laminated to the board. These are chosen by the shaper together with the board owner and cannot be changed.
Interchangeable fins can be inserted into those surfboards that contain boxes into which they allow the fins to be screwed.
Interchangeable fins can be secured in the box or removed with a keel wrench. The specialized wrench allows the adjustment of the small screws that are embedded in the boxes or keel supports.
Keel box system
There are four main fin box systems allowing them to be interchangeable; FCS, FCS2, FUTURES and US BOX.
The box system thus determines the type of interchangeable fin base that can be inserted into the box of your board.
Fin size
Fin size plays a big difference in how you and the board perform in the water.
A larger keel will have more grip and more control in larger waves.
A smaller fin will have a looser feel and be more forgiving. However, in larger waves, you will lack momentum and control.
A medium sized keel will provide optimal performance in all types of waves.
Keel configuration
It is essential to understand the configuration of your board's fins so that it best suits your surfing conditions.
Flip your board over and look at the tail of your board. The number of fin boxes you see is the configuration and usually ranges between 1 and 5.
The most common surfboard fin configurations are Single, 2+1, Twin, Thruster, Quad and 5-Fin.
The traditional surfboard fin configuration is the single fin box, commonly used on longboards. Individual fins will provide stability, control and predictability to your board.
Single fin boxes are longer to allow you to move the fin forward for a looser feel, or further back for more control.
Tip: When trying a new single fin for the first time, place the fin in the center of the box for a couple of waves and then move the fin forward or backward to find the sweet spot that suits your style surfing.
2+1 configurations have a single longboard fin box in the middle, with 2 side fin boxes on each side, also known as side bites.
Most common in high performance longboards, eggs and SUP
Twin fins or twin fins setup will make your surfboard fun and maneuverable.
Twin fin setups are ideal for smooth wave riding and commonly come in fish shapes and fun boards.
Twin fins offer a skate feel and longer, longer turns.
Thruster is the most common setup these days.
Thruster works well as it adds stability, control and maneuverability for beginners to professional surfers.
The front fins are angled towards the board stringer and are laminated flat to increase support. The central keel is symmetrical on both sides (50/50 Foil) for greater stability.
The quad fin configuration provides speed in smaller waves by channeling water in two directions one toward the end of the surfboard and one out the tail for acceleration.
The two fins near the rails of the board will also add stability and grip in big wave surfing, plus they are great for generating driving turns.
The 5 fin configuration allows you to mix and match fins depending on surfing preferences and conditions.
Switch from the freedom of a twin fin, to the traction of a thruster, to the speed of a quad without changing boards.
Technical procurement
Height, also known as depth, is measured from the base of the keel to its highest point.
The deeper the keel, the more grip, the shorter the depth, the less grip. Shorter fins will give a loose feel and make turning easier.
The base length is the widest point of the keel and is the part that is in contact with the board.
Longer fin bases allow more water to pass through, allowing the board to move faster.
A shorter keel base will allow for tight turns.
The inclination of a keel or rake is defined as the extent to which the leading edge of a fin arches rearward. The pitch or sweep angle is a measurement that determines how far back the fin curves relative to its base.
The more rake, the more grip the keel will have but its ability to make short turns or pivots will be less.
The toe or splay is defined as the angle of the lateral fins in relation to the stringer of the board. The side keels are normally angled inwards to create pressure on the outer shell. This creates a more responsive feel.
Fin Cant is the degree of outward angle a fin has in relation to the bottom of your surfboard. If a fin has a pitch of zero, its position is straight up and down at right angles to your board. This is going to be fast in a straight line, but it won't be as responsive in turns. If the keel cant is greater, it allows for more response through turns. It means you can maintain a little more momentum when the board is leaning over the rail.
The flex of a fin determines projection and versatility in the sense that it can be used on a variety of different boards, from high performance shortboards to longboards and nose riders. Generally, flexible fins have a wide base, which tapers to a narrow tip.
A fin with more flex allows you to have a little more error, but a stiffer fin will respond in a timely manner when you need it.
The foil refers to the shape and geometry of the inner and outer faces of the keel. The foils directly affect the flow of water over the surface of the keel.
Here are some of the details about the main types of foil:
Flat : The inner face of the keel is flat and the outer face is convex, to achieve a balance between turning capacity and grip. They can be seen on the side keels of the propellers (tri-fins) or on some Twins.
Inside : The inner face is concave while its outer face remains convex. This shape serves to eliminate friction with the water to generate greater speed.
80/20 : Without being completely symmetrical, it makes you feel the control that a rear keel offers without losing stability. Typically used as a trailer for Quad fins setup.
50/50 (symmetrical) : The two sides are symmetrical, so the flow of water generates control and grip. It is used on both rear fins and longboards.
Helpful tips:
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Stiff boards with small, flexible fins with a little camber will be fun to ride.
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Soft or loose boards will go faster and have better momentum with large, stiff fins with more lean.
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The position of the Single Fin in relation to the tail will change the feel of your board. Move forward to create a looser feel. Fit further back to create support and control.
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Boards with more rocker may be better with a larger fin setup.
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Boards with wider tails will do better with a larger fin setup.
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Boards with a smaller, stiffer fin setup will be more responsive.
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When you ride a shorter board in bigger waves, you will need larger, steeper fins.
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Typically larger surfers will need larger fins, the same goes for smaller surfers who have smaller fins.