Non symmetrical trailing edge (rudders)

[danielro]

hello, in the last years i've seen non symmetrical trailing (aft) edges in flat or almost flat rudders or boards of small sailing dinghies, i suppose that the possibly benefit is related to minimize the vortex down the profile but i do not know exactly how works this type of shape and his influence it's really relevant.
Best regards.
Daniel Rguez.
Las Palmas. Canary Island.

[Doug Lord]

You might check out a copy of Larsson and Eliasson"s "Princibles of Yacht Design" on page 128, Fig 6.30: "Influence of trailing edge geometry on vibration level".The page shows 8 different trailing edge shapes. Among the best shapes are a symetrical wedge shape with the wedge angle under 30° and an asymetric 45° cutoff as long as "the corner on the cut-off side is smoothed". The primary benefit is to eliminate vibration/noise at boat speeds where resonance occurs.

[danielro]

As you point, should be useful for high speeds, perhaps planning speeds in dinghies, according the book, only to avoid the possibly vibration due to the "incorrect" way the flow leave the edge. Here i've seen rudders or boards of dinghies with one side totally flat and the other side with a trailing edge with an angle of approx. 30 degrees or less. If the book says that is needed a high speed to be efficient, only should be effective for rudders in courses downwind never while go to windward. I suppose this fact makes the asymmetrical edges not useful for boards (normally being in up position while going down).
Regards
Daniel