4.8″ fins 2-pack, set area 20.28 sq. inches



  • Total area: 10.14 sq. inches
  • Area, set of 2: 20.28 sq. inches
  • Height/depth: 4.8 inches
  • Stiffness: Semi-flex or stiff
  • Gloss black, orange, blue, or matte black
  • Fits FCS


FinSciences 4.8 fins 2-pack has a total set area of 20.28 square inches, and is for sidebites in a 2 + 1 setup, or as part of a thruster or quad setup.

These fins are comparable in hold and drive to more typical 4.25-inch dolphin fins that have area of around 14.5 square inches each, a set total of 29 square inches.  So swap out those big, old, draggy fins, and put in some of these smaller fins for performance gains.

We chop off about 30 percent of the least efficient area of older fin designs, then reposition and reconfigure things a bit, for a fin that looks different and works better.


  • Total area: 20.28 sq. inches (10.14 sq. inches times two)
  • Height/depth: 4.8 inches each fin
  • Rake/sweepback: 22 degrees
  • Foil section: symmetrical (double)
  • Winglets area alone: 0.9 sq. inches
  • Planform area alone: 9.75 sq. inches
  • Fits FCS

Sizing of FSI Fins Compared to Typical Fins

Our fins have a lot of power–hold and drive. 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.  Read more about lift, drag, hold and drive.

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.    

$25.00Select options

Additional information

Weight 2.2 oz
Dimensions 5 × 3 × 1.0 in
Select stiffness and color, then ADD to CART

Stiff, in matte black, Semi-flex, in gloss black, Semi-flex, in translucent blue


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