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How ducting a propeller increases efficiency and thrust
How ducting a propeller increases efficiency and thrust
Published: 2015/07/22
Channel: RCModelReviews
Trailer: Powerful Ducted Propeller with Washing Machine Motor
Trailer: Powerful Ducted Propeller with Washing Machine Motor
Published: 2017/01/07
Channel: The Post Apocalyptic Inventor
More on ducted propellers, the Q-tip propeller
More on ducted propellers, the Q-tip propeller
Published: 2015/08/29
Channel: RCModelReviews
More on ducted propeller systems
More on ducted propeller systems
Published: 2015/07/27
Channel: RCModelReviews
Ducted Wind Turbine Doubles Performance at Clarkson University
Ducted Wind Turbine Doubles Performance at Clarkson University
Published: 2017/01/04
Channel: Clarkson University
miniquad 250 Ducted X8 Beerlift 2015
miniquad 250 Ducted X8 Beerlift 2015
Published: 2015/08/31
Channel: FliteClub
Building a Ducted Propeller with a Washing Machine Motor
Building a Ducted Propeller with a Washing Machine Motor
Published: 2017/01/16
Channel: The Post Apocalyptic Inventor
Dynamic Stability and Control Characteristics of a Ducted Fan Model in Hovering Flight
Dynamic Stability and Control Characteristics of a Ducted Fan Model in Hovering Flight
Published: 2011/04/05
Channel: NASA Langley CRGIS
Self adjusting Propeller by Hy-Generation
Self adjusting Propeller by Hy-Generation
Published: 2016/02/16
Channel: Hy-Generation
Ducted Fan Simulation in OpenFOAM
Ducted Fan Simulation in OpenFOAM
Published: 2015/05/12
Channel: OpenFOAM Tutorials
RC ducted fan Vertical takeoff and landing aircraft
RC ducted fan Vertical takeoff and landing aircraft
Published: 2016/04/25
Channel: RC NEWS
First HunterKiller EDF Tricopter
First HunterKiller EDF Tricopter
Published: 2013/09/13
Channel: MainDesign IT
Ducted Fan Static Thrust Test Rig
Ducted Fan Static Thrust Test Rig
Published: 2012/11/26
Channel: Klever Freire
Propeller Outboard marine Guard
Propeller Outboard marine Guard
Published: 2014/11/04
Channel: russ
RC scratch built MIG 15 with ducted propellers . Maiden flight
RC scratch built MIG 15 with ducted propellers . Maiden flight
Published: 2016/07/17
Channel: RC Airplanes Victor
The Case For Ducted Fan VTOL
The Case For Ducted Fan VTOL
Published: 2011/10/07
Channel: AVIDLLC
Project Elise- Ducted propeller test
Project Elise- Ducted propeller test
Published: 2008/07/10
Channel: Unknown
Ducted propeller project by Sławek Maiden Flight
Ducted propeller project by Sławek Maiden Flight
Published: 2014/01/05
Channel: robflyrc
Solidworks fluid simulation of a ducted fan, with rotating region
Solidworks fluid simulation of a ducted fan, with rotating region
Published: 2016/11/29
Channel: UVIC CAD CAE CAM
Kort Nozzle, Prop tests, and Pizza.
Kort Nozzle, Prop tests, and Pizza.
Published: 2015/11/16
Channel: J Mantzel
Ducted Prop Assembled
Ducted Prop Assembled
Published: 2014/01/24
Channel: Eric Schwartz
Inventors revolutionise boat propeller system
Inventors revolutionise boat propeller system
Published: 2012/09/10
Channel: Newshub
ROV Thrusters - Part 3 - Testing Props
ROV Thrusters - Part 3 - Testing Props
Published: 2014/03/18
Channel: SV Seeker
VTOL single ducted propeller
VTOL single ducted propeller
Published: 2017/07/22
Channel: Sarang Kadam
Fleye Ducted-Fan Drone now on Kickstarter
Fleye Ducted-Fan Drone now on Kickstarter
Published: 2016/01/11
Channel: Roswell Flight Test Crew
Rotating ship props
Rotating ship props
Published: 2014/12/10
Channel: CCE LTER
Nano Tornado Camera Drone: World
Nano Tornado Camera Drone: World's Safest Drone
Published: 2015/05/21
Channel: Nano Tornado
1933 Stipa-Caproni Aircraft
1933 Stipa-Caproni Aircraft
Published: 2014/06/27
Channel: The Retronaut
SUPER FAST X 49A Helicopter for US military
SUPER FAST X 49A Helicopter for US military
Published: 2014/06/20
Channel: USA Military Documentaries
"Ducky" EDF Quadcopter - first test flight
"Ducky" EDF Quadcopter - first test flight
Published: 2014/03/02
Channel: phreakmonkey
Tilt Drone duct quick test
Tilt Drone duct quick test
Published: 2015/10/29
Channel: FliteClub
Investigative 1/4 build of full scale quadcopter part 2 DIY propeller
Investigative 1/4 build of full scale quadcopter part 2 DIY propeller
Published: 2014/10/29
Channel: amazingdiyprojects
FT009 ducted prop test
FT009 ducted prop test
Published: 2016/07/27
Channel: David Beaver
Efficient propeller / amphibious quadcopter build
Efficient propeller / amphibious quadcopter build
Published: 2014/09/27
Channel: amazingdiyprojects
Ducted Prop Assembled
Ducted Prop Assembled
Published: 2014/01/25
Channel: viron11111
Project Elise- Ducted propeller test #2
Project Elise- Ducted propeller test #2
Published: 2008/07/22
Channel: Unknown
Waterjet propulsion action | waterjet propeller| pump- jet
Waterjet propulsion action | waterjet propeller| pump- jet
Published: 2017/05/13
Channel: Ship channel
JJRC H36 - Ducted Propeller drone (Headless Mode, Return to home, 360° Flip)
JJRC H36 - Ducted Propeller drone (Headless Mode, Return to home, 360° Flip)
Published: 2017/04/13
Channel: furulevi
FuriBee F36 REVIEW great indoor flyer with ducted propellers
FuriBee F36 REVIEW great indoor flyer with ducted propellers
Published: 2017/01/02
Channel: Quadcopter Patrol
The Davidson Boat Propeller
The Davidson Boat Propeller
Published: 2006/12/24
Channel: nzinvent
Why use multi-bladed props?
Why use multi-bladed props?
Published: 2016/04/14
Channel: RCModelReviews
Ducted Propeller UAV VTOL Flight
Ducted Propeller UAV VTOL Flight
Published: 2015/06/02
Channel: Luis Sanchez
Piasecki X-49: What
Piasecki X-49: What's Special About SpeedHawk Helicopters?
Published: 2017/05/24
Channel: Dung Tran
Ducted Fan Bixler
Ducted Fan Bixler
Published: 2013/01/26
Channel: Francisco Carabaza
Deformación tobera - Ducted propeller deformation
Deformación tobera - Ducted propeller deformation
Published: 2009/10/19
Channel: Compass information
AUV Free Running Test _ Nozzle Propeller
AUV Free Running Test _ Nozzle Propeller
Published: 2014/01/09
Channel: Tae Hwan Joung
CFD NUMITALIA AUTOGRID DUCTED PROPELLER GRID
CFD NUMITALIA AUTOGRID DUCTED PROPELLER GRID
Published: 2009/04/02
Channel: Massimiliano Tarrini
General Dynamics Convair VTOL Ducted Propellor Free Fligh HACL Film 00318
General Dynamics Convair VTOL Ducted Propellor Free Fligh HACL Film 00318
Published: 2014/06/16
Channel: sdasmarchives
AUTOGRID DUCTED PROPELLER GRID 2
AUTOGRID DUCTED PROPELLER GRID 2
Published: 2014/03/01
Channel: NUMITvideo
CFD NUMITALIA AUTOGRID DUCTED PROPELLER GRID 2
CFD NUMITALIA AUTOGRID DUCTED PROPELLER GRID 2
Published: 2009/04/02
Channel: Massimiliano Tarrini
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WIKIPEDIA ARTICLE

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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 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.

Advantages are increased efficiency at lower speeds (<10 knots), better course stability and less vulnerability to debris. Downsides are reduced efficiency at higher speeds (>10 knots), course stability when sailing astern, and increase of cavitation. Ducted propellers are also used to replace rudders.

History[edit]

Luigi Stipa[1] and later Ludwig Kort (1934)[2] demonstrated that an increase in propulsive efficiency could be achieved by surrounding the propeller with a foil-shaped shroud in the case of heavily loaded propellers. A "Kort Nozzle" is referred to as an accelerating nozzle and is generally a MARIN 19A profile[clarification needed] or a MARIN 37 profile.

Advantages and disadvantages[edit]

Kort nozzles or ducted propellers can be significantly more efficient than unducted propellers at low speeds, producing greater thrust in a smaller package. Tugboats and fishing trawlers are the most common application for Kort nozzles as highly loaded propellers on slow moving vessels benefit the most. Nozzles have the additional benefits of reducing paddlewheel-effect (e.g. the tendency of a right-hand wheel to back to the left) and reduce bottom suction while operating in shallow water.

The additional shrouding adds drag, however, and Kort nozzles lose their advantage over propellers at about ten knots (18.5 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.

Shrouding of this type is also beneficial to navigation in ice fields since it protects the propeller tips to some extent. However, ice or any other floating object can become jammed between the wheel and nozzle, locking up the wheel. Fouled wheels in Kort nozzles are much more difficult to clear than open wheels.

A research paper by Bexton et al. (2012)[3] concluded that ducted propellers were the likely cause of fatal injuries of seals in the northeastern Atlantic. The authors hypothesized that the seals were drawn through the nozzle and past the rotating propeller blades, incurring curvilinear lacerations to skin and muscle tissue. This type of injury has come to be known as a "corkscrew" injury. The authors also comment that other animals, including harbour porpoises, have been seen to exhibit similar injuries.

Types[edit]

There are two types of ducts; accelerating and decelerating. With accelerating ducts, the inflow velocity and efficiency of the propeller is increased. This is the type that is used on heavily loaded propellers or propellers with limited diameter. As Ludwig Kort performed extensive research on this type, it is often called a "Kort nozzle".

With the second type, the inflow velocity is reduced, whereby pressure is increased, reducing cavitation. This is called a pump-jet, especially in combination with fixed blades or stators.

NACA 4415.

MARIN has done extensive research on ducted propellers. Many of the used profiles are based on the NACA airfoils of which the NACA 4415 has very good characteristics. Most commonly used are nozzle 19A and 37 of the MARIN series. These have a rounded trailing edge to ease fabrication and increase efficiency sailing astern. Initially, the propellers of the Wageningen B-series were used, later the Kaplan-type with a wider blade tip.

Physics[edit]

Circulation around accelerating and decelerating nozzle
Circulation around nozzles.svg

dT = Thrust
dL = Lift

pu: Negative pressure
po: Positive pressure

In a Kort nozzle, the inflow velocity is increased, reducing pressure. This lowers thrust and torque of the propeller. At the same time, a circulation occurs, resulting in an inward aimed force, that has a forward component. The duct therefore has a positive thrust. This is normally larger than the thrust reduction of the propeller. The small clearance between the propeller and duct reduces tip vortex, increasing efficiency.

As drag increases with increasing speed, eventually this will become larger than the added thrust. Vessels that normally operate above this speed are therefore normally not fitted with ducts. When towing, tugboats sail with low speed and heavily loaded propellers, and are often fitted with ducts. Bollard pull can increase up to 30% with ducts.

With decelerating ducts, the circulation opposite of the Kort nozzle, resulting in a negative thrust of the duct. This type is used for high speed vessels with increased exposure to cavitation and vessels that want to reduce noise levels, such as warships.

See also[edit]

References[edit]

Bibliography[edit]

External links[edit]

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