Fins Part Two: What animal should we model fins after?
When you're picking fins for your surfboard, you're probably not thinking about pilot whales. But according to recent research, maybe you should be. Scientists from Michigan Tech University have been studying fin shapes inspired by marine creatures to find the perfect design for surfboard stability and speed.
The fin has revolutionized surfing since its introduction in the 1930s. Without it, we'd all be skidding sideways down wave faces with zero control. A fin provides lift against the sideways force of a surfer's movement, allowing for those satisfying carves and cutbacks and concurrently freeing us from becoming the mid-30’s dude with long hair and a van that hates fins. Fins are essentially doing the same job as a keel on a sailboat - converting sideways force into forward motion while providing directional stability.
What makes a fin perform well comes down to the balance between lift and drag. Lift pushes perpendicular to the direction of water flow, helping you grip the wave face when turning. Drag is the resistance the fin creates as it moves through water, slowing you down. The holy grail of fin design is maximizing lift while minimizing drag.
This is where marine creatures enter the picture. Aquatic mammals and fish have been refining their dorsal fins through millions of years of evolution. Their primary function is directional stability while swimming - exactly what we need on our surfboards. The Michigan researchers tested nine different bio-inspired fin shapes including those modeled after blue sharks, shortfin mako sharks, blue marlins, killer whales, spotted dolphins, and various whales.
Using both computer modeling and physical experiments in water channels, they found that the Short-Finned Pilot Whale fin shape at a 10° angle of attack consistently provided the highest lift-to-drag ratio. When set at this angle, the water flow around the fin remained smooth with minimal separation, keeping drag forces low while maintaining solid lift.
What happens when you crank that angle higher? Beyond 25°, the researchers observed significant flow separation and swirling eddies behind the fin. These turbulent vortices dramatically increase drag without adding much more lift. It explains why fins set at extreme angles might feel grippy at first but ultimately slow you down.
The physics plays out whether you're surfing mushy beach break or pumping harder than a Texas oil rig. At typical surfing speeds (3-7 meters per second), the pilot whale-inspired fin maintained its superior lift-to-drag performance across all conditions.
This complements what we already understand about fin design from the first article. The base length of your fin (where it attaches to the board) affects acceleration - longer bases generally allow for faster speed generation. Fin depth (how far it extends into the water) provides hold and lateral stability. Meanwhile, sweep (or rake) - the angle from mid-base to the tip - influences how tightly you can turn.
For practical application, this research suggests that if you're looking to optimize both speed and maneuverability, a fin shape resembling a pilot whale's dorsal fin set at approximately 10° would be your best bet. Interestingly, many high-performance fins already incidentally approach this design, though perhaps not intentionally mimicking pilot whales.
While materials science has given us carbon fiber, honeycomb cores, and all manner of composite constructions, it seems the most fundamental aspect of fin design - its shape - is best borrowed from creatures that have been ripping waves for far longer than humans have been standing on boards.
Further Reading:
Nice. Have you seen those fins inspired by the pectoral fins of humpback whales? they've got all those bumps and knobs. It's super interesting.
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0232035
As an average surfer, I can feel the difference between a cheap plastic fin and a proper fin, but the difference between $50 standard fins and $200 signature models is beyond my ability.
You already know that, despite my background in science, I am
usually sceptical about the influence of science on design. Most studies are done in conditions that are only rough approximations of actual surfing. So yeh, in general what you say is true but the reality remains that board and fin design progress by a selection process rather than from a theoretical base.