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.