{{short description, Mechanical device to propel a vessel 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 A propeller (colloquially often called a screw if on a ship or an airscrew if on an aircraft) is a device with a rotating hub and radiating blades that are set at a pitch to form a helical spiral which, when rotated, exerts linear thrust upon ...

. The Kort nozzle, pump-jet and

rim-driven thruster The rim-driven thruster, also known as rim-driven propulsor/propeller (or RDP) is a novel type of electric propulsion unit for ships. The concept was proposed by Kort around 1940, but only became commercially practical in the early 21st century ...

are examples. An example propulsor is shown in the accompanying picture. It has a shroud which cuts down on blade-tip

cavitation Cavitation is a phenomenon in which the static pressure of a liquid reduces to below the liquid's vapour pressure, leading to the formation of small vapor-filled cavities in the liquid. When subjected to higher pressure, these cavities, cal ...

and radiated noise. It also has a rotor element and a

stator The stator is the stationary part of a rotary system, found in electric generators, electric motors, sirens, mud motors or biological rotors. Energy flows through a stator to or from the rotating component of the system. In an electric mot ...

. The stator concentrates the thrust in axial direction and reduces energy wasted in the tangential flow (therefore eliminating torque on the hull). The number of blades in the rotor and stator will typically be two different prime numbers to avoid

standing wave In physics, a standing wave, also known as a stationary wave, is a wave that oscillates in time but whose peak amplitude profile does not move in space. The peak amplitude of the wave oscillations at any point in space is constant with respect ...

s. The blades in the rotor or the stator may be angled to further reduce noise. The physical design and layout is very much similar to a single stage axial-flow compressor.

Other propulsors

Voith Schneider

The Voith Schneider Propeller, also known as a cycloidal drive is a specialized marine propulsion system. It is highly maneuverable, being able to change the direction of its thrust almost instantaneously. It is widely used on

tug A tugboat or tug is a marine vessel that manoeuvres other vessels by pushing or pulling them, with direct contact or a tow line. These boats typically tug ships in circumstances where they cannot or should not move under their own power, suc ...

s and ferries. From a circular plate, rotating around a vertical axis, a circular array of vertical blades (in the shape of

hydrofoil A hydrofoil is a lifting surface, or foil, that operates in water. They are similar in appearance and purpose to aerofoils used by aeroplanes. Boats that use hydrofoil technology are also simply termed hydrofoils. As a hydrofoil craft gains sp ...

s) protrude out of the bottom of the ship. Each blade can rotate itself around a vertical axis. The internal gear changes the

angle of attack In fluid dynamics, angle of attack (AOA, α, or \alpha) is the angle between a reference line on a body (often the chord line of an airfoil) and the vector representing the relative motion between the body and the fluid through which it is m ...

of the blades in sync with the rotation of the plate, so that each blade can provide thrust in any direction, very similar to the '' collective pitch control'' and '' cyclic'' in a helicopter.

Azimuth thruster

An azimuth thruster is a configuration of ship propellers placed in pods that can be rotated on the horizontal plane, making a rudder unnecessary. These give ships better maneuverability than a fixed

and rudder system.

Magnetohydrodynamic drive

A magnetohydrodynamic drive or MHD propulsor is a method for propelling seagoing vessels using only electric and magnetic fields with no moving parts, using magnetohydrodynamics. The working principle involves electrification of the propellant (gas or water) which can then be directed by a magnetic field, pushing the vehicle in the opposite direction. Although some working prototypes exist, MHD drives remain impractical and exist mostly in the world of science fiction. A magnetohydrodynamic drive was featured in the 1990 film ''The Hunt for Red October'', differing from the pump jet propulsion system featured in the Tom Clancy novel '' The Hunt for Red October'' upon which the movie was based.

External links

Rolls-Royce MarinePleuger PropulsionTug boat FAQUltraJet web siteZF Marine
Marine propulsion de:Düsenringpropeller

Other propulsors

Voith Schneider

Azimuth thruster

Magnetohydrodynamic drive

See also

External links