We did some Computational Fluid Dynamics (CFD) studies to help see and illustrate the flow of water around a typical surfboard fin, and FinSciences’ fins with finlets.
Water flowing into a typical fin creates a swirl or vortex around the fin tip. This vortex is evidence that water flows from the high- to the low-pressure side of the fin, making the fin less efficient—less powerful—than it could be.
Here is another view of a typical-surfboard-fin-tip vortex. Typical fins make up for their lack of efficiency—lack of power—by adding surface area. But adding more area means a bigger fin and more skin-friction drag.
FinSciences’ fins with finlets inhibit water flow around the fin tip, making the fin more efficient, so it can be smaller than other fins while producing the same or more power. This is why airplane wings have winglets.
Finlets inhibit the flow of water around the fin tip’s high-to-low pressure side.