The challenge with dagger rudders is to control venting from the surface. As you turn, water
flowing over the lea side of the rudder
pulls air down the full span of the rudder
, dramatically reducing its effectiveness, and creating much more drag for a given amount of steering power
. This is why big daggerboard cats have fixed spade rudders. Balanced spade rudders require the least amount of steering
effort, making autopilots possible.