I know of Luiz' idea, as I have a Mega Cat racing windsurfer (one design class) with this very daggarboard design. High aspect, variable angle with recessed well, controlled with your foot.

The only drawback I see is that in the "kickback" position, I would think there would be a lot more force on the gudgeon if you were trying to steer, and could possibly cause failure in that area.

I'm sure there is a way to work out the control lines so that you can secure the rudder in the down or mid-down postion. My only question is when my leeward rudder kicks back when I'm on the wire in a blow with the spin up. The I-20 system works mildly okay, as I just need to drive deep and push the tiller bar (which can occasionally be done from the center/windward side of the tramp. If I had to go to the leeward hull and fiddle with lines while I try to steer and my crew yells at me, I guess I could be in trouble...

And with that "T" rudder, if you are flying a hull, would that direct forces in the wrong direction? I can understand how it works on those Hobie Raves, since I think they don't roll (I think that's the term), but a cat pitches, rolls, and yaws...