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Azimuth thruster
Azimuth thruster
Azimuth thruster
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Siemens Schottel azimuth thrusters

An azimuth thruster is a configuration of marine propellers placed in pods that can be rotated to any horizontal angle (azimuth), making a rudder redundant. These give ships better maneuverability than a fixed propeller and rudder system.

Types of azimuth thrusters

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Azimuth thrusters on the tug Oued el Kebir, with Kort nozzles

There are two major variants, based on the location of the motor:[citation needed]

  1. Mechanical transmission, which connects a motor inside the ship to the outboard unit by gearing. The motor may be diesel or diesel–electric. Depending on the shaft arrangement, mechanical azimuth thrusters 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 a horizontal input shaft, a vertical shaft in the rotating column and a horizontal output shaft, with two right-angle gears.
  2. Electrical transmission, 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 Friedrich W. Pleuger and Friedrich Busmann (Pleuger Unterwasserpumpen GmbH), ABB Group's Azipod 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 RMS Queen Mary 2.[1]

Mechanical azimuth thrusters can be fixed installed, retractable or underwater-mountable. They may have fixed pitch propellers or controllable pitch propellers. 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 drilling rigs and drillships.

Advantages and disadvantages

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The French Navy Mistral-class amphibious assault ship Dixmude manoeuvering in Jounieh bay; the wake at the stern is perpendicular to the ship, indicating the use of her azimuth thrusters.

Primary advantages are maneuverability, electrical efficiency, better use of ship space, and lower maintenance costs.[citation needed] Ships with azimuth thrusters do not need tugboats to dock, though they may still require tugs to maneuver in difficult places.[citation needed]

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.[citation needed] Another disadvantage is they increase the draught of the ship.[citation needed]

History

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English inventor Francis Ronalds 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.[2]

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 for the invention.[3] This kind of propulsion was first patented in 1955 by Pleuger.[4]

In the late 1980s Wärtsilä Marine, Strömberg and the Finnish National Board of Navigation developed the Azipod thruster with the motor located in the pod itself.[citation needed]

See also

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References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Azimuth thruster

View on Grokipedia
from Grokipedia
An azimuth thruster is a marine propulsion device featuring a propeller housed in a rotatable pod or gondola that can swivel 360 degrees around a vertical axis, enabling omnidirectional thrust without relying on separate rudders or steering mechanisms. This design integrates propulsion and steering into a single unit, typically driven by mechanical or electrical systems, and is mounted either underwater in the hull or as a retractable bow thruster. The origins of azimuth thrusters trace back to 19th-century innovations in steerable propellers, with early concepts like the "propelling rudder" patented by in 1859. However, the modern form emerged in the mid-20th century, when Joseph Becker, founder of Schottel, invented the transmission in 1950, allowing efficient power transfer through a Z-shaped shaft arrangement for horizontal . Advancements continued with electrical podded designs, such as ABB's introduced in the late , where the is housed directly in the underwater pod for simplified installation and reduced mechanical complexity. Azimuth thrusters are classified into mechanical types like Z-drives (with horizontal input and Z-shaped gearing) and L-drives (vertical motor to horizontal output), as well as electrical variants including pusher ( behind the pod) and ( ahead) configurations. They offer key advantages such as superior low-speed efficiency, precise , reduced noise (especially in units, up to 20 dB lower), and halved crash-stop distances compared to conventional systems, though they can be vulnerable to damage in shallow waters or grounding. Widely applied in cruise ships, ferries, icebreakers, offshore supply vessels, and naval craft, these thrusters have become standard for new constructions requiring high maneuverability, with power ratings ranging from 185 kW to over 8 MW.

Fundamentals

Definition and Purpose

An azimuth thruster is a steerable marine propulsion device consisting of a propeller housed in a rotatable pod or gondola, mounted externally below the hull, that enables 360-degree horizontal rotation to direct thrust in any desired direction without requiring a separate rudder. This configuration integrates propulsion and steering into a single unit, allowing vessels to achieve omnidirectional movement efficiently. The primary purpose of azimuth thrusters is to significantly improve vessel maneuverability, especially at low speeds, during docking and berthing operations, and for maintaining precise in challenging conditions such as offshore oil platforms. By eliminating the need for traditional rudders and associated mechanical linkages, these thrusters reduce hydrodynamic drag and fuel consumption, enhancing overall operational efficiency and simplifying vessel design. Emerging as a mid-20th-century , azimuth thrusters provided a practical alternative to fixed and systems.

Basic Principles

The physics of in an azimuth thruster relies on Newton's third law of motion, which states that for every action, there is an equal and opposite reaction. The accelerates water backward, generating a forward on the vessel as the reaction to the change in water . This propulsive vector can be directed in any horizontal orientation, while torque for rotating the thruster unit is provided through the bearing, enabling precise alignment without additional rudders. Rotational allow the azimuth thruster to 360 degrees around a vertical axis, aligning the axis with the required direction for or maneuvering. This is achieved using hydraulic or electric drives that actuate the rotation, typically responding at rates of 10-12 degrees per second to support . The drive system transmits to the bearing, ensuring smooth reorientation of the pod relative to water flow. Efficiency in thrust modulation depends on the propeller configuration and its interaction with incoming water flow. Fixed-pitch blades provide high at the design speed but require variable rotational speed for adjustment, achieving lower in reverse due to flow reversal limitations. Variable-pitch blades, in contrast, allow direct adjustment to optimize across speeds, though they may consume additional power at idle unless RPM is reduced, enhancing overall hydrodynamic by matching to . The direction of the resultant thrust T⃗\vec{T}
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