A
ducted propeller, also known as a
Kort nozzle, is a
propeller fitted with a non-rotating
nozzle. It is used to improve the efficiency of the propeller and is especially used on heavily loaded propellers or propellers with limited diameter. It was developed by
Luigi Stipa (1931) and
Ludwig Kort (1934). The Kort nozzle is a shrouded propeller assembly for marine propulsion. The
hydrodynamic design of the shroud, which is shaped like a
foil, offers advantages for certain conditions over bare propellers.