joi, 24 mai 2012

Types of azimuth thrusters

An azimuth thruster is a configuration of shippropellers 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.

There are two major variants, based on the location of the motor:

1.Mechanical transmission, where a motor inside the ship is connected to the pod 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.
2.Electrical transmission, where an electric motor is 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. and Mr. (Pleuger Unterwasserpumpen GmbH), ABB Azipod was the first product using this technology.
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.
Primary advantages are electrical efficiency, better use of ship space, and lower maintenance costs. Ships with azimuth thrusters do not need tugs 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.
Later, subsidiaries of ABB, also based in Finland, developed the Azipod thruster, with the motor located in the pod itself. This kind of propulsion was first patented in 1955 by Pleuger of Germany.

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