Leading edge radii of less than .500 inch, in sideview, are prohibited on outboard hydroplanes and runabout fins. Leading edges are defined as any edge that can be seen in front view. Bottom fins on runabouts also fall under this rule.

Justification
The efficiency of the cut resistant material is a function of the velocity, mass and area shape of the penetrating object. An accident during the 2019 season indicated that the sharp point on a turning fin could apply extreme pressure to the material. The rounding of the leading edge, even thought sharpened, lessens the change of penetration. This radius is just slightly larger than the radius of a quarter, which makes for a simple gauge.

Fin Shape Radius
Minimum .500 in. radius on the forward, lowest, leading edge. Take into account the angle that the fin is mounted on the boat.
1. Angled back on the boat, radius two points (unless angled enough to lift middle point).
2. Angled back, no need to radius.
3. Radius front point, even if angled back.
4. Radius front, radius back if deeper than front when angled.