FinSciences 9¼” fin

FinSciences 9¼" fin 1



Total area: 30.6 in²
Template/planform area: 29.1 in²
Finlets area: 1.5 in²
Height/depth: 9.25 in²
Rake/sweepback: 15°
Anti-cavitation trailing edge
Stiffness: Semi-flex or stiff
Colors: Gloss black, orange, blue, clear, or matte black
Fits Fins Unlimited and Bahne fin boxes

SKU: nine-quarter-fin Category:

WG2 fin for longboards and SUP

FinSciences 9.25 inch fin is 30.6 square inches in area, and is designed for surf and SUP. This fin takes less horsepower to move through the water, so surfers can catch waves more easily, and can surf longer. And in crowded lineups where the first surfer on the wave owns it, it's easier to accelerate to speed and jump on the wave.

For SUPers, paddling is easier. Less horsepower to move your fin through the water means you can paddle further, for longer, and faster.

We ran numbers, horsepower, coefficients of lift versus drag, and other numbers, to objectively measure fin performance. We didn't just dream up a design.

The result is a fin that produces the same amount of hold and drive (aka lift--see post) as other fins, but with a smaller surface area.

Less drag, more fun! Faster fin, better acceleration, better turning, longer sessions! That's what these fins are about!

Check out our fin-size calculator >>


  • Height/depth: 9 inches
  • Total area (with winglets): 30.6 sq. inches
  • Planform area alone: 28.5 sq. inches
  • Winglets (finlets) surface area: 1.6 sq. inches (about the size of a US quarter)
  • Rake/sweepback angle: 15 degrees
  • Fits Fins Unlimited and Bahne Boxes
  • The WG2 is a second-generation fin, and is just over 30 square inches.  Compared to our first-generation fin, we moved the winglets to the end of the fin to increase overall performance.  We decreased the size of the winglets a bit to decrease drag even more.  And we added a bit more sweepback, or rake, to help shed kelp, while still maintaining a very high aspect ratio and low taper ratio--in other words, it provides excellent hold, good drive, accelerates quickly, and paddles easily.

Ever miss that perfect wave by half a stroke?  If your fin had less drag,  you'd have caught it!

Ever lose a wave to somebody who paddled in just a bit faster than you?  If you'd been able to accelerate faster, it could have been your wave!

Ever feel like conditions are great, but you've been out so long your arms have turned into limp spaghetti noodles?  With less drag, you would have lasted longer and caught more waves!

Ever make a sharp cutback, or even a sharp right or left when trying to catch a wave, only to stall out and lose it?  A better turning fin that doesn't stall so easily would help.

Ever wish you could ride the small waves in marginal conditions?  Less drag makes it easier to catch them!

Ever wish you could go faster to get to part of a wave that looks a little better? A faster fin would make it happen!

Winglets have been used on aircraft for quite awhile now, people are used to seeing them on the end of airplane wings. But winglets also are used on submarines, on some rotor blades, on the ends of race car spoilers or air dams, and on boat keels. Winglets, or a version of them, were conceived decades ago, but not put into use until after Richard Whitcomb of NASA and Boeing studied their ability to reduce fuel costs by decreasing induced drag. Whitcomb found that winglets reduce induced drag by about 20 percent, while improving the lift-to-drag ratio by about 6 percent, findings that Boeing confirmed.

Check out this article about Richard Whitcomb, NASA, and Boeing's research on winglets--or try doing some of your own research on the topic--we don't make this stuff up.

The purpose of winglets--or finlets--on a surfboard fin is to inhibit the migration of water from the high-pressure to the low-pressure side of the fin, as when turning or exerting side pressure, in order to increase the efficiency of the fin overall. If you're a paddler--whether you're into SUP, kayaks, or canoes--you've seen the top of a vortex in two dimensions at the water surface with each stroke of your paddle. Water sneaks around the paddle's edges, moving from the high-pressure to the low-pressure side. The same water movement from one side to the other occurs with surfboard fins when you put pressure on one side or the other. As the fin and board move through the water, the swirl elongates into a vortex, evidence of the water movement from the high- to the low-pressure side of the fin.

In fin design we could make up for inefficiency by adding surface area. Many fins are designed this way--they're big. In other words, if the fin doesn't produce lift real well, just add more area, that'll get the turning force or hold that you need. In the '50s, '60s, and early '70s, engine design in cars followed a similar thought process. "Just make the engine bigger." Few cared much about efficiency then, so powerful engines were large, sucked lots of gas, and the cars to support them were heavy. Then came the energy crisis of the '70s, and folks started thinking in terms of efficiency.

Why do we care about fin efficiency or whether we add more area to surfboard fins or SUP fins?

Because adding more area adds drag. Every square inch of fin is skin-friction drag. Bigger fin, more drag. Drag slows you down, makes it harder to paddle, slower to accelerate, and causes you to burn more energy to catch a wave--meaning shorter surf sessions before your arms give out. So if we can get the hold and drive we want, why not have the smallest fin you can get away with? Read more about fin sizing on our FAQs page.

Any by the way, the winglets are not intended as hyrdofoils--they are WAY too small to lift you out of the water . . . and they are not designed to hold down the tail while you walk to the nose. Winglets aren't magic--just science.

This Wavegrinder 2 fin for longboards and SUP has several features designed to maximize fin efficiency.

  • A high-aspect-ratio shape (tall and thin)
  • A low taper ratio
  • A short base
  • A cutaway
  • A bulbous forefoot
  • A NACA double-zero foil section
  • Winglets

Additional information

Weight13.1 oz
Dimensions9 × 5 × 1.2 in
Stiffness & Color:

Semi-flex clear, Semi-flex gloss black, Semi-flex translucent blue, Semi flex translucent orange, Stiff matte black


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