Quad set, four 5.7″ fins, set area 58.32″ sq.



  • Area: 14.58 sq. inches
  • Area set of 4: 58.4 sq. in.
  • Height/depth: 5.68 inches
  • Stiffness: Semi-flex or stiff
  • Color: Black, orange, blue or matte black
  • Fits FCS
SKU: FSI-03 Category: Tags: , , ,


This set is comprised of four of FSI’s shortboard fin large size, each of which is 5.7 inches tall and 14.58 inches in area.

Available in semi-flex black, in semi-flex translucent blue, and and in matte-black stiff. 

This larger shortboard fin quad set is for heavier surfers and boards that need more turning force.

The key design concept behind our fin, as with modern airplane wings and boat keels, is that we chop off about 20 to 30 percent of a typical fin’s inefficient area, then reposition about 5 percent, and add it back on as winglets or finlets. So we lose a bunch of draggy inefficient area, and what we keep is efficient, fast, and performs really well.

The end result is that our fins are smaller than other fins, yet the produce similar hold and drive–i.e. lift–but with less drag.  Read more about hold, drive, lift and drag.

Every square inch of fin you have in the water creates friction–it’s skin-friction drag.  So if you have less fin area, you’ll have less drag, quicker acceleration, easier paddling, and longer surf sessions before your arms tire.

See our other products–you can mix and match with the small fins to get the amount of area that works right for you and your board.


  • 5.68 inches tall, but thin, high-aspect ratio.
  • Area, total for the set: 58.32 sq. inches (13.38 sq. inches in each fin, plus 1 sq. inch in the winglets = total area of 14.58 square inches per fin.  But our fins behave 30 percent or so larger than they are, so you might need fewer or smaller fins than you’re used to.  See the calculator below.
  • Sweep/rake angle: 21.93 degrees
  • Foil: double, i.e. symmetrical double-zero
  • Semi-flex, or stiff
  • Anti-cavitation trailing edge
  • Color: glossy black (semi-flex), translucent blue (semi-flex), or matte black (stiff)
  • Fits FCS

Adapter available: If you want to fit this fin into a standard longboard fin box, try this link.

Shipping is approximately $10-12 in domestic U.S. and internationally, about $18-$42, depending on number of fins purchased and on shipping options. Three of these weigh in at less than 13 ounces, so I can ship them via First Class (US about $4, international about $16), instead of Priority Mail (US about $7, international about $40). If your cart shipping charges vary from these amounts significantly, contact us with your desired order and your exact shipping address, we’ll recalculate the charges for the cheapest rate available, and send you an invoice via PayPal. If you live in New Zealand, check http://www.nzpost.co.nz/tools/youshop to see whether you can use it as a shipping intermediary, in which event it gives you a US address for shipping.

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

FSI fins produce more lift than their size suggests–this is the key concept of FSI fins. The smaller area still gets good hold–and the smaller area means less drag, more speed, acceleration, easier paddling, and longer surf sessions.

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, then try downsizing–try pulling off the sidebites and going with a single Wavegrinder or Wavegrinder 2 longboard-SUP fin. You will dramatically decrease the area, 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  Wavegrinder 2 30.60 sq. in. 61.20 sq. in.    


Additional information

Weight 7.0 oz
Dimensions 6.5 × 3.1 × 1.2 in
Select stiffness-and-color combo, then ADD to CART

Stiff, matte black (4), Semi-flex, gloss black (4), Semi-flex , translucent blue (4), Semi-flex 2 black, 2 blue


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