что это угол расхождения рулей относительно ДП (вместо положения, когда оба пера строго параллельны ДП):

The final adjustment should a slight toe out of the blades away from the center line of the boat. In other words the aft edges of the blades will be further from the center line than the front edges of the blades. This is done by adjusting the end caps on the tie bar. Only toe out by a 1/2" on each side. This assures that there is always some water pressure against the blade faces when underway. This reduces any rattle and slows down undue wear.
http://www.bertram31.com/proj/tips/rudders.htm
[картинка там же]

но как его правильно назвать, не знаю...