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Finformation: Basic and next-level guide to how fins work






Design Theory

Learn as much (or as little) as you want to about surfboard fins with the below guide

Surfersvillage Global Surf News, 14 July, 2016 - Surfboard fins are both fun and inherently confusing. We all have a general working knowledge of template, rake, foil and surface area and how that translates to the way the fins work. But there is always more to know. For those of us who have become stuck in a knowledge vacuum on fin design, we present the below guide which features the latest finformation in both a BASIC and NEXT LEVEL presentation., a subscription based service modeled after Netfilx but for surfboard fins, were kind enough to provide their detailed NEXT LEVEL finformation on the finer details of surfboard fin performance. 

The most knowledgeable gear geeks will learn something here. And, if you’re just processing this design information for the first time, the BASIC descriptions below are a great starting point to build your knowledge on design theory.


Fin Size



BASIC: Generally, a larger fin has more hold and control. This is great for generating speed or holding through hard turns. Conversely, a larger fin will take more force to initiate turns and will not release as quickly. Smaller fins will be more forgiving and loose but won’t provide as much drive. However, they will respond to quick direction changes and won’t stick or track.

NEXT LEVEL: Fin size is an interesting one, because there are a lot of factors, the most important being your personal height and weight. A smaller surfer would tell you that a small fin holds just fine, while a larger surfer would say the same set of fins is way to loose, that said we also need to take into account surf style. If you like a loose style, you may actually want to go with a fin that's slightly smaller than the recommended fins in your weight range. However, if you’re a smaller surfer with a real heavy back foot, you may find you need a bit bigger fin to accommodate your style of surfing.


Fin Template and Shape

BASIC:  All fins have their own unique shape. Some tend to stand more straight up and down, while others curve and reach way back. But you can’t just say “I like a curvy template” because all the components work together to create the fin’s performance characteristics.

NEXT LEVEL: When we're talking about fin template, we're also talking about what type of wave you're surfing. If you like drawn out arching turns, then you want a more "curved" fin or a fin with a lot of rake, but here's the catch. A fin with a lot of rake won't get you long drawn out turns if you're not surfing a wave with a long drawn out open face. Hence, the converse is also true, if you like tight, in the pocket surfing, you want a more "strait up and down" fin, or a fin with less rake. Again, a fin with less rake won't help your in the pocket style surfing if the wave is more drawn out and doesn't have much of a pocket.


Fin Base

BASIC: The larger the base of the fin and more surface area it covers, the more drive a fin will give you when you pump or do turns. Conversely, the less base there is to the fin, the less drive you will have while turning becomes a bit easier. 

NEXT LEVEL: We feel that fin base is a bit more straight forward. If the waves are fast, hollow and barreling, you want more base. In waves of consequence you're looking to pick a line and stick that line, you're not necessarily looking to snap off the lip over reef that's been sucked dry, unless of course, you're on tour.


Fin Height 

BASIC: As with fin base and overall size, the taller a fin is the more hold and stability it will have while a shorter fin will give more release and quicker turning capabilities.

NEXT LEVEL: Fin height and overall size are kind of interesting and here's our unique perspective that we've learned from Finatic. While the difference in height between a "small" fin and a "medium" fin can be as little as 1/10 of an inch, (Yes, that's One Tenth of ONE inch) depending on the base of the two fins, that can change the total surface area of that fin by an inch and a half. Still, that might not sound like a big deal. HOWEVER, let's multiply that by three or four depending on whether you're riding a thruster or quad and you get 4 1/2 to 6 inches difference in total surface area of your board touching the water! (We not even completely sure if the fin companies measure the suffice area of both sides of the fin, so one might argue that these numbers then need to then be doubled.) This leads us to the conclusion that, if you’re worried about your new board being 6'0" and not 6'1", you're not worried about the right numbers as we've just proven 1/10 of an inch can put up to 6 inches or more surface area touching the water and that's HUGE.

Fin Foil 

BASIC: Fin foil helps determine how water moves past the fin when surfing. The fin foil is what the fin looks like when you look at it straight-on, like it’s coming right at you. The foil is the hydrodynamic shape from leading edge (the thickest part) to the trailing edge (the thinner part). Foils can be either flat on one side, even on both sides, or some mix of the two. Some foils are concave in the inside part like fins with FCS’ Inside Foil Technology and Future’s Vector Foil. Generally the side fins for your setup will have a flat or concave inside foil and the rear fins will be symmetrical.

NEXT LEVEL: If you want to get extremely technical you have 50/50 foil which is almost exclusively used on rear fins and you have 80/20 foil, which is mostly held exclusively for quad rears. It's fairly easy to understand given some context, the numbers represent percents. So 50/50 would mean that half of the curve is on one side and half of the curve is on the other side, or the fin has a "symmetrical foil". It's also easy to see why a 50/50 foiled fin would be used almost exclusively as a rear fin, as that fin is your pivot point and you wouldn't want to turn to the right or to left faster would you? No. You want a smooth transition at that pivot point while turning, so you want a 50/50 foil. Giving that information, the 80/20 foil probably already makes more sense to you and you can probably already see why it would be used as quad rears. With a quad you have two pivot points instead of one, since those pivot points are off from the center line, you would want more foil on the outside of the fins, thus the 80/20, 80% of the curve on the outside and 20% on the inside. That said, we have Finatic members that have tried both 50/50 foiled quad rears and 80/20 foiled quad rears and prefer one over the other. Honestly, at that point it probably has more to do with the tail of the board and how far apart your rear fins are as to which foil you prefer.

Now, onto the outside fins, which typically use either a flat foil or a vector foil. Your flat foil is more traditional, you'll need to generate more of your own speed, so generally speaking they're better in more powerful waves. That said, a vector foil (of which there are many types) will give you more hold. So if it gets EXTREMELY heavy you may want to try a vector foil. Vector foils have a concave curve on the inside of the fin, long story short this actually helps the water adhere to the fin, giving it more water to surface contact. A vector foil will generate more of it's own speed and therefore generally is better in smaller, more mushy waves. It should be noted that some of FCS's fins and Futures Vector II fins have a concave base and a flat tip on the inside of the fin. This provides a very interesting solution to the extra hold a vector foiled fin has, as the flat tip allows for the release that you're used to with a flat foiled fin, while the concave base helps generate that extra speed you might be looking for.


Fin Cant

BASIC: This is the angle the fin tilts from base to tip if you’re looking at the fins from straight on. A fin with a lot of cant will slant outward in relation to the bottom of the surfboard. If the fin has no cant it will appear straight up-and-down from the bottom of the board.

More cant equals more responsiveness through turns. Less cant means more speed when holding a straight line.

NEXT LEVEL: This concept is much more simple than it sounds, your typical fin with have some slight amount of cant. When thinking about it when your board is on rail your fin isn't at a 90 degree angle with surface of the water anymore. The more you're on rail the more you lose that angle and some point we've all hit zero degrees with the water line and slid out. Unfortunately for us, this usually happens on a hard bottom turn and what proceeds is a trip over the falls. Well, this could be attributed to the fin cant. The more cant a fin has, the closer it would be to that 90 degree angle when on rail and the better chance you have of your fins not sliding out and thus why most fins have some level of cant. Cant isn't always listed within the manufacturer’s descriptions, but we imagine anything from 2 to say 14 degrees is a typical amount of cant. Unfortunately, the only way to decide what you personally like here is to look down your board at your fins and compare one sets cant to another, if your board feels alive when your using a fin with more cant and you're holding through some steep hard bottom turns, those may be the fins for you.


Fin Toe-In

BASIC: If you look down the bottom of your board from nose to tail, the fins should draw an imaginary line to the tip of the board. Some fins will draw the imaginary line to the stringer, a bit below the nose, or out to the rail. This angle is called toe-in. More toe-in equals more responsiveness at the sacrifice of speed.

NEXT LEVEL: While a fin can account for some minor level of Toe-In, the real play here is with the shaper. Depending on their experimentation with the shape of the board they have set the ideal Toe-In by setting the fin boxes at their desired angle. Which poses an interesting question, when your messing with the Toe-In of a fin. (which is hard to do) What you're really doing is going against what the board manufacturer intended. If we step back to a very broad overview, we would say, "Wow that's not good". However, surfing is a feeling and that's personal. You may like a bit more or less Toe-In than the manufacturer intended, but generally speaking they shape boards for a living and you don't. lol


Fin Flex 


BASIC: The most technical aspect of fins. All fin-makers play around with various formulas of construction affect a fins’ flex pattern. It’s generally agreed that fins with a stronger base and more flexible tip work best, which is why you’ll see FCS and Futures. 

NEXT LEVEL: Ah YES! Fin Flex... This is interesting right? This would be the only element that absolutely affects all of the other elements we've discussed thus far. I mean seriously, a bigger fin with more flex may feel to loose? And a smaller, more stiff fin may have to much hold? I mean we've gotten as technical as we can with all the fin characteristics listed above and now we throw fin flex in there and the whole thing gets out of whack. The best way to explain this is easy, flex is 100% a feeling and again, a feeling is personal. Do you like more or less flex? We don't know, that's for you to decide and that's why some pro's surf Glass Flex while others surf Solid Glass, Hex Core, Solid Carbon or some variation there of. What is true about technology and flex, is that the fin manufacturers can design a fin to flex in a particular way which is EXTREEMLY useful. That said, if you're comfortable, you feel in control, if you fell in control you surf better, so flex is extremely important, but it's also the most subjective aspect of a fin. I mean that's like telling someone they need more milk in their cheerios... Just because you like more milk, doesn’t mean they do, it's objective, we can't tell you if you'd like your favorite fin template with more or less flex, you need to experiment.

There are so many factors when picking fins, wave type, board type and personal feel among others that all come into play. Fins are fun and inherently confusing, because there's some level of objectivity. They change a way a board feels, they change the way you surf and it's easy to hold all other variables consistent and just mess with the fins.  It will always be the opinion of Finatic that you need to own multiple sets of fins for different conditions and different boards, but at the same time you need access to every fin for experimentation and evolution and that's what Finatic allows.


Finformation, Basic, Next-level, Guide, How fins work, Fin Size, Fin Foil, Fin Height, Template, Shape
Bryan Dickerson & Chris H

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