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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.
There are two major variants, based on the location of the motor:[ citation needed ]
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.
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 ]
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.
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, ABB Group developed the Azipod thruster with the motor located in the pod itself.[ citation needed ]
A propeller 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 a working fluid such as water or air. Propellers are used to pump fluid through a pipe or duct, or to create thrust to propel a boat through water or an aircraft through air. The blades are shaped so that their rotational motion through the fluid causes a pressure difference between the two surfaces of the blade by Bernoulli's principle which exerts force on the fluid. Most marine propellers are screw propellers with helical blades rotating on a propeller shaft with an approximately horizontal axis.
On a ship, the engine room (ER) is the compartment where the machinery for marine propulsion is located. The engine room is generally the largest physical compartment of the machinery space. It houses the vessel's prime mover, usually some variations of a heat engine. On some ships, there may be more than one engine room, such as forward and aft, or port or starboard engine rooms, or may be simply numbered. To increase a vessel's safety and chances of surviving damage, the machinery necessary for the ship's operation may be segregated into various spaces.
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. The Kort nozzle, pump-jet and rim-driven thruster are examples.
A saildrive is a transmission system for a boat whose inboard engine has a horizontal output shaft. The saildrive's input shaft is therefore also horizontal. That input shaft is geared so as to drive a vertical intermediate shaft extending downward through the hull. The intermediate shaft is then geared so as to drive a horizontal propeller shaft mounted on a skeg outside the hull.
Contra-rotating, also referred to as coaxial contra-rotating, is a technique whereby parts of a mechanism rotate in opposite directions about a common axis, usually to minimise the effect of torque. Examples include some aircraft propellers, resulting in the maximum power of a single piston or turboprop engine to drive two propellers in opposite rotation. Contra-rotating propellers are also common in some marine transmission systems, in particular for large speed boats with planing hulls. Two propellers are arranged one behind the other, and power is transferred from the engine via planetary gear transmission. The configuration can also be used in helicopter designs termed coaxial rotors, where similar issues and principles of torque apply.
The Voith Schneider Propeller (VSP) is a specialized marine propulsion system (MPS) manufactured by the Voith Group based on a cyclorotor design. It is highly maneuverable, being able to change the direction of its thrust almost instantaneously. It is widely used on tugs and ferries.
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.
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. They were developed in Finland jointly by the shipbuilding company Masa-Yards and the ABB Group, which produces them.
MS Arcadia is a cruise ship in the P&O Cruises fleet. The ship was built by Fincantieri at their shipyard in Marghera, Italy. At over 84,000 gross tonnage (GT), Arcadia is the second smallest of seven ships currently in service with P&O Cruises. The ship officially entered service with the company in April 2005 and was named by Dame Kelly Holmes.
Manoeuvering thrusters are transversal propulsion devices built into, or mounted to, either the bow or stern, of a ship or boat to make it more manoeuvrable. Bow thrusters make docking easier, since they allow the captain to turn the vessel to port or starboard side, without using the main propulsion mechanism which requires some forward motion for turning; The effectiveness of a thruster is curtailed by any forward motion due to the Coandă effect. A stern thruster is of the same principle, fitted at the stern. Sufficiently large vessels often have multiple bow thrusters and stern thrusters.
The Kitchen rudder is the familiar name for "Kitchen's Patent Reversing Rudders", a combination rudder and directional propulsion delivery system for relatively slow speed displacement boats which was invented in the early 20th century by John G. A. Kitchen of Lancashire, England. It turns the rudder into a directional thruster, and allows the engine to maintain constant revolutions and direction of drive shaft rotation while altering thrust by use of a control which directs thrust forward or aft. Only the rudder pivots; the propeller itself is on a fixed shaft and does not.
The Pleuger rudder is a power assisted ship's rudder. It creates a flow of water in the direction the rudder points powered by an auxiliary electric motor. This aids maneuverability at low speeds greatly, since it operates on a similar principle to a thruster.
A Schilling rudder is a specific type of profiled rudder used on certain boats and ships.
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 direction and eliminating the need for a conventional rudder. This form of power transmission is called a L-drive because the rotary motion has to make one right angle turn, thus looking a bit like the letter "L". This name is used to make clear the arrangement of drive is different from Z-drive.
A ducted propeller, also known as a Kort nozzle, is a marine propeller fitted with a non-rotating nozzle. It is used to improve the efficiency of the propeller and is especially used on heavily loaded propellers or propellers with limited diameter. It was developed first by Luigi Stipa (1931) and later by Ludwig Kort (1934). The Kort nozzle is a shrouded propeller assembly for marine propulsion. The cross-section of the shroud has the form of a foil, and the shroud can offer hydrodynamic advantages over bare propellers, under certain conditions.
A double acting ship is a type of icebreaking ship designed to run ahead in open water and thin ice, but turn around and proceed astern (backwards) in heavy ice conditions. In this way, the ship can operate independently in severe ice conditions without icebreaker assistance but retain better open water performance than traditional icebreaking vessels.
A Flap Rudder is a specific type of multi-section rudder used on boats and ships. The hinged aft section gives the rudder an extra control surface, enhancing its efficiency.
The rim-driven thruster, also known as rim-driven propulsor/propeller 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 due to advances in DC motor controller technology. As of 2017, commercial models of between 500 kW and 3MW are available from manufacturers such as Rolls-Royce, Schottel, Brunvoll, Voith, Van der Velden, etc.
Schottel is a manufacturer of propulsion and steering systems for ships and offshore applications. The company founder Josef Becker invented the rudderpropeller, a z-drive, in 1950. Today the company develops and manufactures azimuth propulsion, maneuvering and steering systems. In 2014 the subsidiary Schottel Hydro was founded to bundle up the company activities in the hydrokinetic energy segment.
Röthelstein is an Austrian river icebreaker owned by Verbund AG. She is used to break ice and push barges on the Danube river. Built by Kværner Masa-Yards in Finland in 1995, she was the first new vessel to be fitted with Azipod propulsion units.