Fin Terminology

We will explain the terminology and principles behind the elements that define the characteristics of fins:

Base

The length of the horizontal part where the fin meets the surfboard.

A longer base enhances drive power and facilitates speed gain. Conversely, a shorter base improves turning performance and makes turning easier.

Depth

The length (height) of the vertical part of the fins protruding from the surfboard into the water.

Greater depth increases stability but also increases turn resistance. Conversely, smaller depth results in smoother turns but sacrifices stability.

Area

The area where the fin extends outside the fin box.

A larger area enhances stability and drive power but increases resistance. Conversely, a smaller area facilitates easier turns.

For longer boards and heavier riders (and boards), a larger area is required.

Sweep

The angle of inclination of the fin.

A greater sweep angle increases stability and drive power but also increases turn resistance. Conversely, a smaller sweep angle improves turning performance, results in smoother turns, and reduces turning radius.

Foil

Bulges on both sides of the fins.

Foil controls water flow. The "50/50" configuration, with bulges on both sides, is commonly used for center fins. The "Flat" configuration, flat on the inner surface and bulging on the outer surface, is commonly used for side fins.

Cant 

The angle at which the fin is tilted from a vertical angle of 90 degrees to the bottom surface of the surfboard.

Center fins are usually at 0 degrees (perpendicular to the board), while side fins are angled a few degrees. This angle increases water resistance when the board is tilted, enabling sharp turns.

【Reference】https://pocketsurf.jp/surfboard_fin