Inefficient for what? Turning/Course Correction/Brake? Inefficient compared to paddle work or a skeg?

I assume for course correction is your question. Too many variables to give a definite #. speed (note there is no eficiency loss at 0 speed), rudder shape and size, leaned boat or not, how much resistance is considered inefficient.

: My question is, how many degrees should a rudder be able to turn or rotate
: (left/right) before it becomes inefficcient?

: Glen in Baie-St-Paul.