5.7″ fins 2-pack, set area 29.16 sq. inches



  • Area per fin: 14.58 sq. inches
  • Area, set of 2: 29.16 sq. in.
  • Height/depth, each fin: 5.68 inches
  • Foil:  symmetrical (double)
  • Anti-cavitation trailing edge
  • Fits FCS
SKU: FSI-03 Category: Tags: ,


FinSciences 5.7″ fins in a 2-pack are for use on bigger boards, boards that are longer or harder to turn, and for use as part of a thruster set or quad set.

The fins come in semi-flex black or translucent blue, and in stiff (matte black). They fit FCS.

Our basic design concept is that we take a typical fin, then chop off about 30 percent of the area, adding back about 5 percent where it does the most good, as winglets or finlets. This creates a fin that is a but smaller than others that have similar hold and drive–our fins are more efficient, so they turn better, go faster, and are easier to paddle.

See http://href=”https://finsciences.com/surfboard-fin-lift-drag-hold-drive/

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.

Heavier surfers (185-plus) can use three, lighter surfers can probably get away with only two–especially if you have a five-slot board–you can use the rear quad placement.  And you can mix and match with the small fins.


  • Area: 13.38 sq. inches in the fin, 1 sq. inch in the winglets = total area of 14.58 square inches–but behaves like it’s 30 percent larger, so you might need only two.
  • Depth: 5.68 inches–tall, but thin, high-aspect ratio.
  • Sweep/rake angle: 21.93 degrees
  • Foil: double, i.e. symmetrical double-zero
  • Semi-flex, or stiff
  • Anti-cavitation trailing edge
  • Color: glossy (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 a stiffness-and-color combo, then ADD to CART

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


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