Azimuth thruster

(Also called pod drive ) Azipod is the name for a drive unit for boats and aircraft.

Shipping

The drive is covered by a streamlined nacelle, and rotatable 360 degrees around the vertical axis. The propeller is attached as a tractor propeller on the front of the nacelle, as shrouded pusher propeller at the rear of the nacelle or in combinations of one or more free-running train and thrust propellers. In Gondola also the drive in the form of an electric motor can be located.

The "classical" propeller pod is the Schottel rudder propellers ( Schottel drive ), a sheathed by a Kort nozzle thrust propeller, is rotated by 360 ° around the vertical axis, especially under the fuselage of ferries and tugs. He is driven by the engine in the hull over waves and bevel gear.

The propeller pod is technically a consistent further development of the conventional Schottel drive, but without touching the proprietary and patent rights Schottels. Also, is built in a Schottel drive the pusher propeller in a Kort nozzle, while propeller nacelles rotate the propeller without the hydrodynamics influencing protection ring free.

History and manufacturers

The principle of the pod drives was already in 1955 by FW Pleuger and Friedrich Busmann ( company Pleuger Unterwasserpumpen GmbH, Hamburg - today Flowserve Hamburg GmbH) invented as a further development of the active rudder and patented ( and Others Patent 2,714,866, United States Patent Office, August. 1955). At that time, however, was too far ahead of its time. Pioneered the development of today's propeller gondolas were Schottel and Wärtsilä in commercial drives and Volvo Penta in the recreational boating.

Worldwide, there are about six well-known manufacturers for pod drives. These include, among others, the Swiss-Swedish ABB with the Azipod ®, the British Rolls- Royce plc and its Mermaid ® pods or the German conglomerate Siemens in cooperation with the native to Spay to Koblenz Schottel shipyard that since 1997 the SSP (Siemens develop - Schottel propulsion ), produce and market ( this drive has a capacity of up to 20 megawatts, putting it in the top performance category ). Volvo Penta calls its Azipod system IPS and Brunswick / Mercury calls it Cobra.

As described above, the engine manufacturers and shipyards their respective system of propeller gondolas gave its own name, often with the brand and trademark rights.

Systems

Propeller nacelles can be driven purely mechanically or electrically. In the purely mechanical version is located in the hull a diesel engine acting on the propeller shaft located in the nacelle via a mechanical transmission.

With the electric system, there is a partly also the mechanical transmission of an electric drive motor in the hull or integrated into the gondola electric motor with direct coupling of the propeller shaft. In both cases, electric energy is usually generated by a diesel engine with a downstream generator. The location of the diesel and generator unit is independent of the position of the propeller pod.

Propeller nacelles can be equipped either with one or with two propellers. The gondolas with two propellers there are again two systems: either with two corotating propellers (tandem ) or opposite ( contra ). By the counter- rotation is used by the rear propeller of the propeller twist to increase the efficiency. Propeller gondolas with only one propeller can be used as a tractor propeller (propeller located in front of the gondola ) or as a pusher propeller (propeller located at the rear of the gondola ) to be executed.

Ships with 360 ° swivel gondolas usually require no oars, because the gondolas drive and Manövrierorgan connect. By precisely adjusting the propeller jet is at low ship speeds, as given, for example, when creating or holding position, a very good control of the ship. Due to the lack of rudder, however, the rate stability is lower.

When choosing an electric drive, the position of the propeller gondolas is in principle arbitrary. For practical reasons, it is yet classic at the rear, since the maximum leverage is guaranteed to maneuver. Some tug additionally in the bottom of the fore over swing propeller gondolas. The resistance is slightly cheaper, as no attachments such as shafts and shaft blocks influence the wake of the ship. Negative on the other hand, due to its size, the gondolas themselves, so that the part of the manufacturer, a high effort is made to keep this small, or to improve the flow around with the help of small profiles.

The common name comes from the brand name Pod POD company Wärtsilä, this machine is considered the " inventor".

Although the technique seems simple, yet it is complex and requires certain minimum body sizes. This resulted in the recreational boating to other solutions. There, the drive power is, as in Schottel drive, brought on waves and transmission from the engine in the fuselage through the turntable into the gondola. By way of derogation from Schottelsystem no pusher propeller rotates in the recreational boating on a propeller pod but in a Kort nozzle, but rotate in opposite directions two free tractor propeller. Since 2005 this system for both commercial shipping and recreational craft, for the latter but not rotated 360 degrees about the vertical axis, but only around the circle sector necessary for the maneuvering of a sport boat.

In theory, the compact solutions of the recreational boating allow the rotation of the propeller nacelles 360 degrees around the vertical axis. In practice, chimneys are frowned upon but on pleasure boats and exhaust gases through the drives (in this case, the propeller gondolas ) to the outside. The required gas leak in the exhaust system but restricts the rotation of the normal in the recreational boating propeller gondolas on a circle segment.

Both in commercial shipping, as well as in recreational boating are located on the vessels always at least two propeller gondolas, since only then the advantages over classical wave systems so strongly come into play that they make up the high purchase price.

Pros and Cons

Compared to conventional shaft installations bring propeller nacelles the following advantages:

• In conjunction with a diesel-electric drive can adjust high low and part load fuel consumption at lower proportion driving profiles.
• In particular, in the low ship speeds smallest turning circles can be achieved.
• The integration into the ship is usually straightforward, since all the components of the drive come from a manufacturer and at the shipyard must only be installed. In conventional systems, various manufacturers are mostly responsible for each component.
• The stopping times and distances are extremely short, as the gondolas are only rotated and not the motors must be reversed.
• Preventing possible vibration of the propeller, which can be caused by the drive shaft.

However, the propeller nacelles also have some disadvantages:

• The design efficiency is worse than for a conventional plant propeller -shaft motor is usually because either high gear or high conversion losses occur.
• The mass is much greater than with conventional systems.
• The cost is also much higher than with a conventional system.
• Maximum available propeller diameter and thus realizable drive capacities are lower than for conventional drives.

Applications

Many of the famous and biggest cruise ships are equipped with a podded propulsion, such as the Queen Mary 2 ( put into service in 2004 ), the Freedom of the Seas (2006) and is currently the largest cruise ship in the world, Allure of the Seas (2010).

In 2005, which entered service in German research vessel Maria S. Merian has two pod drives, which allow a very good dynamic positioning in scientific work.

The pod system is also used for ice breaking. These shows the propeller in the direction of ice and when reversing the water flow breaks off pieces of ice. An example is the Mastera, an oil tanker with high ice class.

Even with larger warships, the system is used, such as landing ships such as the Spanish Juan Carlos I ( L -61) or helicopter carriers such as the ships of the French Mistral class.

Aviation

In aviation propeller gondolas are mainly known for airships. Here pivotable, on both sides of the passenger cabin attached gondolas around a horizontal axis not only used as drives, but also to the amount of control, especially at low forward speeds, if the effect of the control surfaces is reduced, or, in order to save on -offs and landings personnel.

In a similar system is also based the tiltrotor used for convertible aircraft, its rotational axis between the vertical and horizontal position can be pivoted in flight the " helicopter " into a " plane " (and vice versa) to transform and so the good start and maneuverability of a helicopter with the efficiency of a fixed-wing aircraft to combine. (Examples: Bell - Agusta BA609, Bell V -22 and Bell Eagle Eye).

Description of an Osprey

Rotating propeller nacelle tiltrotor, the Bell - Boeing V-22 Osprey