An azimuth thruster is a configuration of marine
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 ...
s placed in pods that can be rotated to any horizontal angle (
azimuth
An azimuth (; from ar, اَلسُّمُوت, as-sumūt, the directions) is an angular measurement in a spherical coordinate system. More specifically, it is the horizontal angle from a cardinal direction, most commonly north.
Mathematicall ...
), making a
rudder
A rudder is a primary control surface used to steer a ship, boat, submarine, hovercraft, aircraft, or other vehicle that moves through a fluid medium (generally aircraft, air or watercraft, water). On an aircraft the rudder is used primarily to ...
unnecessary. These give
ship
A ship is a large watercraft that travels the world's oceans and other sufficiently deep waterways, carrying cargo or passengers, or in support of specialized missions, such as defense, research, and fishing. Ships are generally distinguished ...
s better maneuverability than a fixed propeller and rudder system.
Types of azimuth thrusters
![Oued el Kebir-IMG 9346](https://upload.wikimedia.org/wikipedia/commons/4/4c/Oued_el_Kebir-IMG_9346.jpg)
There are two major variants, based on the location of the motor:
#
Mechanical transmission
Propulsion transmission is the mode of transmitting and controlling propulsion power of a machine. The term ''transmission'' properly refers to the whole drivetrain, including clutch, gearbox, prop shaft (for rear-wheel drive vehicles), differ ...
, which connects a motor inside the ship to the outboard unit by
gear
A gear is a rotating circular machine part having cut teeth or, in the case of a cogwheel or gearwheel, inserted teeth (called ''cogs''), which mesh with another (compatible) toothed part to transmit (convert) torque and speed. The basic pr ...
ing. The motor may be
diesel
Diesel may refer to:
* Diesel engine, an internal combustion engine where ignition is caused by compression
* Diesel fuel, a liquid fuel used in diesel engines
* Diesel locomotive, a railway locomotive in which the prime mover is a diesel engin ...
or
diesel-electric. Depending on the shaft arrangement, mechanical azimuth thrusters are divided into
L-drive An L-drive is a type of azimuth thruster where the electric motor is mounted vertically, removing the second bevel gear from the drivetrain. Azimuth thruster pods can be rotated through a full 360 degrees, allowing for rapid changes in thrust direc ...
and
Z-drive
A Z-drive is a type of marine propulsion unit. Specifically, it is an azimuth thruster. The pod can rotate 360 degrees allowing for rapid changes in thrust direction and thus vessel direction. This eliminates the need for a conventional rudder.
...
. An L-drive thruster has a vertical input shaft and a horizontal output shaft with one right-angle gear. A Z-drive thruster has a horizontal input shaft, a vertical shaft in the rotating column and a horizontal output shaft, with two right-angle gears.
#
Electrical transmission
Electric power transmission is the bulk movement of electrical energy from a generating site, such as a power plant, to an electrical substation. The interconnected lines that facilitate this movement form a ''transmission network''. This is d ...
, more commonly called pods, where an electric motor is fitted in the pod itself, connected directly to the propeller without gears. The electricity is produced by an onboard engine, usually
diesel
Diesel may refer to:
* Diesel engine, an internal combustion engine where ignition is caused by compression
* Diesel fuel, a liquid fuel used in diesel engines
* Diesel locomotive, a railway locomotive in which the prime mover is a diesel engin ...
or
gas turbine
A gas turbine, also called a combustion turbine, is a type of continuous flow internal combustion engine. The main parts common to all gas turbine engines form the power-producing part (known as the gas generator or core) and are, in the directi ...
. Invented in 1955 by
Friedrich W. Pleuger and
Friedrich Busmann (Pleuger Unterwasserpumpen GmbH),
ABB Group
ABB Ltd. is a Swedish-Swiss multinational corporation headquartered in Zürich, Switzerland. The company was formed in 1988 when Sweden's Allmänna Svenska Elektriska Aktiebolaget (ASEA) and Switzerland's Brown, Boveri & Cie merged to create ...
's
Azipod
Azipod is a trademark azimuth thruster pod design, a marine propulsion unit consisting of a fixed pitch propeller mounted on a steerable gondola ("pod") containing the electric motor driving the propeller, allowing ships to be more maneuverable ...
was the first product using this technology.
The most powerful podded thrusters in use are the four 21.5 MW Rolls-Royce Mermaid units fitted to .
Mechanical azimuth thrusters can be fixed installed, retractable or underwater-mountable. They may have fixed pitch propellers or
controllable pitch propeller
In marine propulsion, a variable-pitch propeller is a type of propeller with blades that can be rotated around their long axis to change the blade pitch. Reversible propellers—those where the pitch can be set to negative values—can also ...
s. Fixed installed thrusters are used for tugboats, ferries and supply-boats. Retractable thrusters are used as auxiliary propulsion for dynamically positioned vessels and take-home propulsion for military vessels. Underwater-mountable thrusters are used as dynamic positioning propulsion for very large vessels such as
semi-submersible
Semi-submersible may refer to a self-propelled vessel, such as:
*Heavy-lift ship, which partially submerge to allow their cargo (another ship) to float into place for transport
*Narco-submarine, some of which remained partially on the surface
*Se ...
drilling rig
A drilling rig is an integrated system that drills wells, such as oil or water wells, or holes for piling and other construction purposes, into the earth's subsurface. Drilling rigs can be massive structures housing equipment used to drill wat ...
s and
drillship
A drillship is a merchant vessel designed for use in exploratory offshore drilling of new oil and gas wells or for scientific drilling purposes. In recent years the vessels have been used in deepwater and ultra-deepwater applications, equipped ...
s.
Advantages and disadvantages
![BPC Dixmude](https://upload.wikimedia.org/wikipedia/commons/a/a2/BPC_Dixmude.jpg)
Primary advantages are maneuverability, electrical efficiency, better use of ship space, and lower maintenance costs. Ships with azimuth thrusters do not need
tugboat
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, su ...
s to dock, though they may still require tugs to maneuver in difficult places.
The major disadvantage of azimuth drive systems is that a ship with azimuth drive maneuvers differently from one with a standard propeller and rudder configuration, necessitating specialized pilot training. Another disadvantage is they increase the draught of the ship.
The pod-variety, where the electromotor is located outside the hull, puts greater demands on the quality of the seal around the propeller-shaft. This is because any leakages of sea-water will shortcircuit the electromotor. This means that the moving parts will have to fit together especially well with tight clearances, and the remaining seal can be done with for instance oil under positive pressure. The oil will both act as a lubricant as well as a hydrophobic seal.
History
English inventor
Francis Ronalds
Sir Francis Ronalds FRS (21 February 17888 August 1873) was an English scientist and inventor, and arguably the first electrical engineer. He was knighted for creating the first working electric telegraph over a substantial distance. In 1816 ...
described what he called a “Propelling Rudder” in 1859 that combined the propulsion and steering mechanisms of a boat in a single apparatus. The propeller was placed in a frame having an outer profile similar to a rudder and attached to a vertical shaft that allowed the device to rotate in plane while spin was transmitted to the propeller.
The modern azimuth thruster using the Z-drive transmission was invented in 1951 by Joseph Becker, the founder of
Schottel in Germany, and marketed as the Ruderpropeller. Becker was awarded the 2004
Elmer A. Sperry Award The Elmer A. Sperry Award, named after the inventor and entrepreneur, is an American transportation engineering prize.
It has been given since 1955 for "a distinguished engineering contribution which, through application, proved in actual service, ...
for the invention.
This kind of propulsion was first patented in 1955 by
Pleuger
Pleuger Industries is a German manufacturer of submersible pumps, thrusters, and plunger pumps. It is based in Hamburg, Germany. The word "Pleuger" is sometimes considered as synonymous for water-filled motors with multi-stage pumps. It is also c ...
.
In the late 1980s,
ABB Group
ABB Ltd. is a Swedish-Swiss multinational corporation headquartered in Zürich, Switzerland. The company was formed in 1988 when Sweden's Allmänna Svenska Elektriska Aktiebolaget (ASEA) and Switzerland's Brown, Boveri & Cie merged to create ...
developed the
Azipod
Azipod is a trademark azimuth thruster pod design, a marine propulsion unit consisting of a fixed pitch propeller mounted on a steerable gondola ("pod") containing the electric motor driving the propeller, allowing ships to be more maneuverable ...
thruster with the motor located in the pod itself.
See also
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References
{{DEFAULTSORT:Azimuth Thruster
Marine propulsion