Someone sent me these pictures anonymously in response to my older posts on trimaran rudder design
We had a couple of white knuckle rides during which I was wishing for a rudder like this. Once when we sledding down 30 foot swells north of Punta Baja (often approaching 16 kts). I also blame the broach we experienced entering Bahia del Sol on our rudder.
Also, note the trim tab on the trailing edge. This is part of a self steering wind vane system. A small force applied to the trim tab by a wind vane or tiller master is amplified (by the passing water) into the larger force needed to deflect the main rudder (in the opposite deflection).