Theoretical max speed - heeling

[snowleopard]

Or to put it another way, some hulls are so cranky when pressed, you need two rudders to keep them pointed in the desired direction.

With today's wide flat sterns, a single central rudder will be breaking the surface when heeled. Twin rudders, normally angled outwards, mean that one is immersed and near vertical while the other is close to or even above the surface. For the same reasons, the fastest offshore racers with canting keels for righting moment have twin angled dagger boards for optimum lateral resistance. Entirely logical and efficient designs for performance hulls though sometimes aped unnecessarily in cruising boats in much the same way as spoilers on family cars that never get anywhere near aerodynamic speeds.