of the propulsion. The accelerating type is used on heavily loaded propellers or propellers with limited diameter. As Ludwig Kort performed extensive research on it, this type is also called a "Kort nozzle".

With the second type, the straight surface of the duct profile on the inside and the bent one on the outside, the inflow velocity is reduced, whereby pressure is increased, reducing cavitation. This is called a pump-jet, especially in combination with fixed blades or variable stators.