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Propulsion - The Kort nozzle

We intend to highlight some of the various propulsion systems frequently used on tugs. Today we start with the Kort nozzle.

Patent - drawing Kort nozzle

The term "nozzle" is derived from the Middle English noselle, meaning "nose". Interestingly, "nozzle" also remains in the English language as a slang term for "nose."

The Kort nozzle is a shrouded, ducted propeller assembly for marine propulsion invented by Ludwig Kort. The hydrodynamic design of the shroud, which is shaped like a foil, offers advantages for certain conditions over bare propellers.

Kort nozzles or ducted propellers can be significantly more efficient than unducted propellers at low speeds, producing greater thrust in a smaller package. For the bollard pull it may produce as much as 50% greater thrust per unit power than a propeller without a duct. Tugboats are the most common application for Kort nozzles as highly loaded propellers on slow moving vessels benefit the most.

The additional shrouding adds drag, however, and Kort nozzles lose their advantage over propellers at about ten knots (18,52 km/h).

Kort nozzles may be fixed, with directional control coming from a rudder set in the water flow, or pivoting, where their flow controls the vessel's steering

sources: Wikipedia, Everything 2, US Patent no. 2,139,594

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[...] (and Kort nozzles) have both advantages and disadvantages when compared to cycloidal drives. The Z-drive is less [...]

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Computer-generated illustration of a Voith Schneider Propeller concept applied to a platform supply vessels. A real ship has been built with this propulsion system, the first of its kind under VSP. The ship is the Norwegian flag, DNV classified, MV Edda Fram, owned by Rederi Østensj?. The vessel was delivered by Astilleros builder of ships from Spain, in June 2007. It has a length of about 86 meters tall, with a beam of 19 meters. Its powered by a diesel electric system with four main engines of 1950kW and an auxiliary 400 kW, 2500 kW VSP feed two propellers and two 1400kW sigs designed for speed of 16 knots

http://www.youtube.com/watch?v=iauMSHROMnw

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Schottel rudder propellers (SRP) are combined propulsion and steering for a yield of up to 6,000 kW, which convert the engine power in an optimum thrust. Because the teams are governed at 360 degrees, you can also use the full performance for maneuvering and dynamic positioning of the boat.

Maximum maneuverability, optimum efficiency, economic service, installation requires little space and easy maintenance - these are some of the features of this robust and reliable propulsion, which has been proven worldwide in all types of vessels under tropic and arctic conditions

http://www.youtube.com/watch?v=QdSH6SBl5hY

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