Rudder configuration

[Stumble]

Hi Stumble,
this sounds either like a case of a typical misnomer, or a case of my mis-interpretation of your idea.
A winglet serves to reduce the induced drag of a hydrofoil (or rudder, or centreboard) and it is placed at or near the foil tip. Once you move it away from the tips and place it in a random position along the hydrofoil span, it is no more a winglet but a T-foil designed for some other function.

So, if it is placed down at the rudder's (or centreboard) tip, then you have a winglet. If it is placed more upwards towards the water surface, then you might have an anti-ventilation fence. A single device evidently cannot perform both functions, because the two phenomena - the foil-tip induced drag and the ventilation - occur at different sides of a foil.

Cheers

For the most part the winglets used on A-Cat rudders are there to provide automatic attitude adjustment for the boat. They act to reduce pitching, not to act as a fence or to reduce tip vortex generation. Some of the newer L and T foils are designed to do that, but come with major structural problems so I doubt they will be adopted widely, at least for some time.

My thought was that it probably doesn't matter much where vertically on the rudder they are placed, though traditionally they have been about 2/3 down the rudder (why that was chosen I have no idea). If instead they were placed much higher, then they may also act as a ventalation fence, preventing aeration.