The main requirement for efficient rowing and smooth power application is the ability to suspend your weight on the handle. The Hanger is the practical solution to a decades long dilemma as to how coaches and athletes can use the ergometer more efficiently for teaching and training.
Thousands of coaches have tried to use the erg as a teaching tool. Many of them have tried to use a boat strap to help add resistance or lock the handle in place. The problem with this is that there is no clean or safe method to attach the strap to the machine. Thus the Hanger.
Go here to see more instructional videos including common errors.