How To Choose the Right Fins

The three most common types of fin boxes are Futures, FCS and FCS II. Futures fins slide into a single slot, while FCS II fins fit into two grooves within the box. Take note that FCS is an older model of fin and is not compatible with FCS II boxes. LokBox and LibTech are other less common models. Take note of whether the surfboard is a thruster, twin, quad or single fin. 

2. How Much Do You Weigh?

Like surfboards, fins are built differently depending on a surfer’s weight. By sizing your fins correctly, you’ll eliminate most of the fin options right off the bat. The rule of thumb is that surfers pushing hard through their turns can size up, and those not pushing as hard can opt for a smaller sin.  

According to REAL Watersports founder Tripp Forman, narrower-tailed boards like smaller fins since they are typically surfed at higher speeds, whereas super-wide-tailed boards like bigger fins to offset the added tail area.

FCS II Size Chart
XS: under 120lbs
S: 120 – 143bs
M: 144 – 176lbs
L: 177 – 198lbs
XL: 198lbs+

Futures Size Chart
XS: 75 – 115lbs
S: 105 – 155lbs
M: 145 – 195lbs
L: 180lbs+

3. What Types of Waves Will You Be Surfing the Board In?

Just like board design varies depending on the waves, fins should be selected based on the waves they’ll be sinking into. Generally, straighter upright fins (meaning the tip is closer to the base of the fin) are better for vertical surfing and fitting turns into a tighter arch. These fins can help in quick, fast-breaking waves where pivots and rapid transitions are needed. Conversely, fins with more rake (the tip is further away from its base) are better suited for drawn-out, longer turns. They will feel solid and more engaged in the wave, leading to more predictable and stable moves. 

4. What’s Your Surfing Style: Aggressive or Free-Flowing?

This question is about fin construction. Surfers pushing hard through turns or riding fast, powerful waves usually are riding stiff fiberglass or carbon fiber.  Conversely, surfers opting to flow through turns or ride softer waves can ride flexible fins that free up the board and speed it along. The key here is to find the Goldilocks fin — something that’s not too stiff and doesn’t hinder your surfing. 

As Tripp explains: “How does “too stiff” feel? Basically, you’re not able to flex the fin and then receive the bonus of that flex, which is a burst of speed out of the turn. A fin that feels too stiff feels like it’s not flexing at all. Conversely, a fin that’s too soft, like plastic fins for most surfers, flexes and washes out, never really springing back effectively. If you have tried a set of carbon-reinforced fins and feel they’re a bit too stiff, try a set of the same template but with fiberglass/honeycomb construction.”

5. Where’s the Foil?

Foil refers to the shape of the side of the fin. It determines how water flows across the fin. In most thruster sets, for example, the two side fins usually have slight concave inside foils. This channels the water over the fins more efficiently than flat foils and helps provide drive and speed when waves are slower and less powerful. The center fin on a thruster is almost always 50/50 or a symmetrical foil. Both sides are exactly the same, resulting in even water flow for stability and control. In the video below by Futures, you'll see Ian Crane adores foiled twin fins because they produce speed in sloppy surf.

6. What’s My Ride Number?

Futures uses an easy-to-use performance measuring system called the Ride Number.  The smaller the number, the stiffer and rigid it feels. The larger the number, the more flex it will generate and the faster it will be. Numbers 7-10 are good for when the surf is soft, gutless, and has no push. 4-7 are good all-rounders, and 1-4 will offer most control. Choose depending on your desired wave, size and fin shape. 

Think of it this way: In big, barreling waves, you don’t want a fin with a high ride number because it’s too flexible. You want stiff, predictable fins that can hold into the wave face and not slide out in critical sections. 

The Final Countdown

Once you’ve applied these criteria on your fin search, you should be able to narrow down the options. There’s a lot to consider, so feel free to ask a professional surfboard shaper or expert for their recommendations. Don't be afraid to swap about fins for the sake of R&D, too. Experimenting with different sizes, construction and conditions will help grow your knowledge base and lead to a more enjoyable time in the water.