The form of the trailing edge is partly responsible for the extent of water eddies in the wake of the fin. The more eddies there are the higher is the braking effect of the fin.
A razor-sharp trailing edge is dangerous, easily damaged and causes disadvantages on all courses except on the run. A square edge is the best solution as the boundary layer material is being sucked into the wake and the lift forces are increased. The diameter should be somewhere between 0.2 and 0.6 mm.