About Eastern Lines, Surfboard Knowledge


“Everything you wanted to know about Surfboard Fins”


Surfboard fins are a crucial design aspect of your surfboard and its overall performance. Choosing fins that will work best for you and your surfboard depends on your size, ability, riding style and the type of surfboard boxes you have.

Glassed-On Fins

Glassed on fins are laminated directly into your surfboard. Glassed on fins are stronger, lighter and can be stiffer than removable fins. However, glassed on fins can be difficult to repair and do not offer you the versatility of removable fins.

Removable Fins

Removable fins are attached to your surfboard using fin boxes. The fins are either held in using screws or tension. In some fin systems the fins are movable within their boxes to even gain more precise placement. The fins are installed and adjusted using fin keys or a screwdriver. Side fins are different than center fins. Be sure you have installed the correct fin in the box before tightening.


Box Types & Compatibility


There are two major fin systems in use on shortboards today. Funboards and Longboards often use two/four boxes on the sides with a larger adjustable fin box in the center.

Dual Tab Fin Boxes

Dual tab fin boxes have been pioneered by FCS Fins. This is the most widely used fin system in the world. FCS recently introduced the FCS II keyless fin system. In addition to not needing tools to install, the FCS II fins can be adjusted within the box. Older FCS fins will also fit in these boxes.

Single Tab Fin Boxes

Single tab fin systems have been produced by several manufacturers, but the Futures Fin system is the other primary system in use today. Easy set screws hold the fins in place.

Dual Tab and Single tab fins are not cross-compatible!

 Choosing your Fin Size

The primary factor in determining which size fins to use in your board is your weight. Choosing the appropriate fin size is the first essential step to choosing the right fins. Once you have decided on a fin size, examine your boards Fin setup. Your board will be outfitted with 1 to 5 boxes.

Fin Size

The following chart is our recommended fin size by rider’s weight range. If you are in between sizes, consider the type or board and waves you will be riding with the particular fin setup. For example, if you are in between size M and L, you might pick M fins for your small wave board and L fins for your big wave board.

Size Grom XS S M L XL
Weight Under 100 Under 120 105-155 145-195 165+ 190+


Fin Configuration

Once you’ve decided on your fin size, it’s important to understand your board’s fin configuration. To determine your board’s configuration, examine the bottom of your surfboard near the tail. The number of fin boxes you see is the fin configuration and will range from 1-5.

Single Fin

A single fin box is most common on longboards and is the most traditional surfboard fin configuration. Turning with a single fin is limited, meaning single fins are ideal for fast, straight shot surfing. Single fins will provide stability, control, and predictability to your longboard. Longboard single fin boxes are long and allow you to move the fin forward for a looser feel, or further back for more control.

Twin Fin

Twin fins or a dual fin configuration will make your surfboard fun, playful, and maneuverable. Two fin setups are not ideal for big-wave riding and are commonly featured on shortboards to enhance their speed. Twin fins offer a skatier feel and longer, more drawn out turns.

Tri-Fin (Thruster)

Nowadays, 3 fins is the most common configuration and can be found on a variety of surfboard shapes and sizes. The two outer fins are closer to the middle of the board, angled towards the board center (“toed-in”) and can be flat on the inside in order to increase water tracking and speed.  The center fin is the closest to the tail and is symmetric on both sides for stability (see Foil for more info). Tri-fins perform well because they add stability, control, and maneuverability that beginners to pros excel on. A thruster configuration also gives you options – ride twin or single if you want!

4 Fin (Quad)

Quad fin configurations offer speed in smaller surf by channeling the water to the end of the surfboard and out the tail for acceleration.  Two fins near the rails of your surfboard will also add stability and hold in big-wave surfing.  Lastly, quad fins are great for generating drive through turns

Five Fin

Five fin configurations are not meant to be surfed with all five fins. Five fin boxes allow you to mix and match fins depending on your preference and the surf conditions. Swap from the freedom of a twin fin, to the traction of a thruster, to the speed of a quad without changing boards.

2+1 Set-up

2+1 configurations have a longboard single fin box in the middle, with 2 regular thruster side fin boxes to each side. The middle box is longer, allowing you to set your middle fin forward or back. This is an increasingly popular fin box configuration on eggs, funboards, SUPs and logs.



The RakeToeBase LengthFoilFlexHeight, and Cant are important measurements of every surfboard fin, and should be considered when choosing your next surf fins. 


The rake, or sweep, is how far the front edge of a fin arcs backwards. Rake or sweep angle is a measurement that determines how far back the fin curves in relation to its base. Fins with a small rake (large offset) help propel the board, are very stable and predictable but are not ideal for making sharp fast turns. On the other hand, fins with a large rake angle and a small offset will allow your board to have a tighter turning radius, but are more “squirrelly” and playful.


The toe or splay of a surf fin is defined as the angle of the side fins in relation to the board’s central stringer. Side fins are typically referred to as “toed-in,” with the front of the fin angled towards the middle of the board. This causes water to pressure the outside of the fins, for increased responsiveness



The base length of the fin is the widest point of the fin, and sits flush with the board once installed. This length can affect how the board will respond to turns. Longer fin bases create trajectories for water to go past – so your surfboard will move faster. If you want to make sharp turns, however, go for a shorter fin base length.



Foil refers to the shape of the outside and inside faces of your fin, thinnest near the tip and thicker near the base. Foil alters the flow of water over the fin surface and has a direct impact on the performance of your fins and board. Middle fins are always symmetrical and convex on both sides (sometimes called 50/50) for even distribution and stability, while outside fins are usually convex on the outside face and flat or curved on the inside. A flat inside face creates a solid balance of control, speed, and playfulness, while a curved or concave inside face maximizes lift with minimal drag, ideal for speed generation and fluidity.



The flexibility of a fin, or lack thereof, can significantly affect the way a surfboard rides. In general, a flexier fin will provide a skatier feel on more playful waves, but a stiff fin is ideal in faster more hollow waves.

It is important to note that high end fins can be both soft and stiff – they have flex patterns. Many fins now have a stiffer base for tracking and stability, with a softer tip that make it easier to break your board loose while turning.

As a rule of thumb, stiffer fins work well for all ability levels; they are forgiving, stable and predictable, creating a solid platform for progression and big wave riding alike. Soft and flexible fins are great for making fast, sharp turns and will give freesurfers a lively feel to their board, but are more difficult to control compared to stiff fins.


The height (often referred to as the depth) is measured from the base of the fin to the tallest point of the fin. This measurement can change your board’s stability and ‘grip’ through turns. For surfers who desire a board that is easy to control, a taller fin will be more forgiving and handle turns in a relaxing manner. Shorter fins do not grip the water as well, but rather allow the board to be more “buttery” when turning, ideal for spin-like maneuverers on the water, for example.



Cant is the tilt of the fin in degrees, in relation to the base of your surfboard. For example, a fin that is straight up down and in the fin box has no cant (90°) and will likely make your ride faster, while anything more than 90° will increase responsiveness. In order to enhance rider-to-board connectivity and responsiveness, especially through turns, you will benefit from canted fins.  The less cant a fin has the more drive and acceleration your board will have but will also be less playful. In turn, the more cant a fin has the looser and more maneuverable your surfboard will feel.