This paper deals with the problems relating to the increase in discharge that EDF had absolutely to tackle for the Kembs propeller units located at the head of the network of the Rhine power plants. The solution consisted in increasing the diameter of propeller runners and in using a new blade design. The result obtained is a 30% gain of excess power. However, after 500 hours' operation, damage has appeared on the pressure side of blades and also, after 3000 hours, on the bottom ring. Calculations and model tests have been done to find out solutions to these problems.