The ducted propeller is a propeller fitted with a non-rotating nozzle. It is used to improve the efficiency of the propeller and is especially used on heavy loaded propellers or propellers with limited diameter. It is also known as a kort nozzle, which 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.