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An azimuth thruster is a configuration of ship propellers placed in pods that can be rotated in any horizontal direction, making a rudder unnecessary. These give ships better maneuverability than a fixed propeller and rudder system.
Types of azimuth thrusters 
There are two major variants, based on the location of the motor:
- Mechanical transmission, where a motor inside the ship is connected to the outboard unit by gearing. The motor may be diesel or diesel-electric. Depending on the shaft arrangement the mechanical azimuth thruster are divided into L-drive and Z-drive. An L-drive thruster has a vertical input shaft and a horizontal output shaft with one right-angle gear. A Z-drive thruster has an horizontal input shaft, vertical shaft in the rotating column and a horizontal output shaft with two right-angle gears.
- Electrical transmission, are 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 or gas turbine. Invented in 1955 by Mr. F.W. Pleuger and Mr. F. Busmann (Pleuger Unterwasserpumpen GmbH), ABB Azipod was the first product using this technology. The most powerful pods delivered are the four 21.5 MW Mermaids, fitted to Queen Mary 2.
Mechanical azimuth thrusters can be fixed installed, retractable and underwater-mountable. They may have fixed pitch propellers (FPP) or controllable pitch propellers (CPP). Fixed installed thrusters are used for tugs, ferries and supply-boats. Retractable thrusters are used as auxiliary propulsion for dynamically positioned (DP) 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 drilling rigs and drillships.
Primary advantages are electrical efficiency, better use of ship space, and lower maintenance costs. Ships with azimuth thrusters do not need tugboats to dock, though they still require tugs to maneuver in difficult places.
The azimuth thruster using the Z-drive transmission was invented in 1950 by Joseph Becker the founder of Schottel in Germany. First applications came in the 1960s under the Schottel brand name and referred to as Rudderpropeller ever since. Joseph Becker was rewarded with the Elmer A. Sperry Award for this invention as a major contribution to the improvement of transportation worldwide.
See also 
- Pleuger rudder
- The Voith-Schneider marine propulsion system can also quickly change the direction of thrust.
|Wikimedia Commons has media related to: Azimuth thrusters|
- Voith Turbo Marine, Voith Radial Propeller
- http://www.rolls-royce.com/marine/products/propulsors/azimuth_thrusters, Rolls-Royce plc, including videos of operation
- Propulsion system for LNG Carriers, Google Answers thread, April 2003
- 1990 - World’s first podded propulsion system, ABB
- Azimuth Thrusters, Ship-Technology.com
- Azimuth Thrusters Types and Configurations, Thrustmaster of Texas
- Flowserve, L-drive Flowserve Pleuger thruster from flowserve.com
- Youtube, movie azimuth thruster L-drive from flowserve.com
- http://www.zf.com/marine - Thrusters from ZF Marine Krimpen (former HRP Thruster Systems)
- http://www.steerprop.com, Steerprop Azimuth Propulsors