Quad set, four 4.8″ fins, set area 40.56″ sq.



  • Total area, set of 4: 40.56 sq. inches
  • Area per fin 10.14 sq. inches
  • Rake/sweepback: 22 degrees
  • Stiffness: Semi-flex or stiff
  • Colors: Glossy black, blue, or matte black
  • Fits FCS
SKU: FSI-08 Category: Tags: , ,


For those who want to juice up their quad-setup board, this will decrease your total fin area quite a bit, and make your board faster as a result.

Quad-setup surfers generally either like lost of hold, or have a board that needs a lot of fin area.  The set of four small FinSciences 4.8-inch fins still has lots of hold, drive, and power.

Each of these FinSciences 4.8-inch fins is similar in hold and drive to much larger 4.25-inch dolphin fins, which have an area of about 14.5 square inches each, but have similar power.  Because FinSciences’ fins are smaller, they have less drag, are easier to paddle and catch waves, and faster.

If you’ve not tried our set of four, we think you’ll be favorably impressed.  We generally recommend starting smaller than you’re used to–see our fin calculator below–but if you’re not ready for that much downsizing yet, try our set of two 4.8s with two 5.7s.

Specs: Quad Set of Four 4.8-inch Fins:

  • Total area, set of 4 smalls: 40.56 sq. inches
  • Area per fin: 10.14 sq. inches
  • Height/depth: 4.8 inches
  • Rake/sweepback: 22 degrees
  • Winglets/finlets area alone: 0.9 sq. inches
  • Planform area alone: 9.75 sq. inches
  • Foil section:  symmetrical (double)
  • Fits FCS

Sizing of FSI Fins Compared to Typical Fins

Our fins have a lot of power. They generate a lot of hold and drive for their small size.  (Read more about hold, drive, lift, and drag.)

Because they have a lot of power, your right-sized FSI fin will have an area smaller than what you’re used to.  And because they are smaller, they have less drag.  This means that you can accelerate more quickly, paddle more easily, or surf longer.

Basically we take a typical fin, chop off about 30 percent of its area, then replace about 5 percent in a more modern configuration.  This removal of surface area and its skin-friction drag, is one of the key concepts behind our fins.  Our fins resemble modern-day airplane wings and boat keels–because the science justifies it.  Our fins are unlike dolphin fins that have dominated the market for the last 50 years.

Winglets are solid science, and they work.

Winglets and other features we use make these fins about 20 to 30 percent more efficient than larger, older styles, so you need to downsize by about 20 to 30 percent as compared to the fin or set of fins you typically use.

Example: If you typically surf a set of mediums in a thruster setup, fins that are usually about 14.5 sq. inches each, you are surfing 43.5 sq. inches of fin. Try our smalls. Our new small is 10.14 sq. inches, and a set of three is 30.42 square inches, a 30 percent reduction in fin surface area, and a 30 percent reduction in skin-friction drag.

Another example: If your longboard or SUP board has a center fin and two sidebites, calculate the area of your current fins, then try downsizing–try pulling off the sidebites and going with a single Wavegrinder 2 longboard-SUP fin. You will dramatically decrease the area of the fin, yet still get good hold and drive because of the winglets and other features of our fins.

FSI Fins, Areas in Sets

Because FSI’s current fins are symmetric, you can either get a set of the same fins, or mix smaller and larger fins to get the ride you want.

Fin type FSI size Area, each Area, set of 2 Area, set of 3 Area, set of 4
Shortboard fin Small 10.14 sq. in. 20.28 sq. in. 30.42 sq. in. 40.56 sq. in.
Shortboard fin Large 14.58 sq. in. 29.16 sq. in. 43.74 sq. in. 58.32 sq. in.
Longboard-SUP fin WG2 30.60 sq. in. 61.20 sq. in.    

Additional information

Weight 8.8 oz
Dimensions 5 × 3 × 2.5 in
Select color-and-stiffness combo, then ADD to CART

Stiff, 4 matte black, Semi-flex, 4 gloss black, Semi-flex, 4 translucent blue, Semi-flex mix, 2 gloss blue + 2 gloss black