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Kort nozzle The towboat Dolphin I in a floating drydock on the Mississippi River in Algiers, Louisiana. A ducted propeller, also known as a Kort nozzle, is a marine 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 ...
Ludwig Kort (1888–1958 [1]) was a German fluid dynamicist known for developing the ducted propeller, or Kort nozzle. In an attempt to reduce canal erosion, Kort discovered that directing the wake of a propeller through a short, stationary nozzle also increased thrust. [2] He submitted a U.S. patent for this technique, which was awarded in ...
A propulsor is a mechanical device that gives propulsion. The word is commonly used in the marine vernacular, and implies a mechanical assembly that is more complicated than a propeller. The Kort nozzle, pump-jet and rim-driven thruster are examples. An example propulsor is shown in the accompanying picture.
Azimuth thrusters (and Kort nozzles) have both advantages and disadvantages when compared to cycloidal drives. The azimuth thruster is less efficient and slower to manoeuvre, but is likely to be cheaper in the short term. Life cycle costs favour the Voith solution, something reflected in the residual value of a Voith water tractor.
Their kort-nozzle allows for a greater bollard pull however it loses its pull at anything over 10 knots (19 km/h; 12 mph) and loses speed in turns. [3] The Ville class are 13.71 m (45 ft 0 in) long with a beam of 4.72 m (15 ft 6 in) and a draught of 2.74 m (9 ft 0 in).
Catawba has two controllable-pitch Kort-nozzle propellers for propulsion. She has two 20-cylinder Diesel engines, GM EMD 20-645F7B, [7] which provide 4,500 shaft horsepower. These can drive the ship at 15 knots. She also has a 300-horsepower bow thruster to improve maneuverability. [6] [8]
The Kort nozzle is a sturdy cylindrical structure around a special propeller having minimum clearance between the propeller blades and the inner wall of the Kort nozzle. The thrust-to-power ratio is enhanced because the water approaches the propeller in a linear configuration and exits the nozzle the same way.
Beyond this point the nozzle diameter becomes the biggest diameter and starts to incur increasing drag. Nozzles are thus limited to the installation size and the loss in thrust incurred is a trade off with other considerations such as lower drag, less weight. Examples are the F-16 at Mach 2.0 [21] and the XB-70 at Mach 3.0. [22]