Azipod

The first commercial 1.5MW Azipod unit (1990), as installed in the Seili waterway service/antipollution vessel. Displayed at the Forum Marinum maritime museum in Turku, Finland

Closeup of one of USCGC Mackinaw's azipods (Lake Icebreaker application, power 3.3MW per unit, in use since 2005)

Azipod is the ABB Group's registered brand name for their azimuth thruster. Originally developed in Finland jointly by Kvaerner Masa-Yards dockyards and ABB, these are marine propulsion units consisting of diesel-electric-driven propellers mounted on a steerable pod.

The distinguishing feature between the Azipod class of propulsion and other azimuthing propulsion devices is that in the Azipod all propulsion power is delivered by an integrated electric motor instead of a mechanical shaft to the vessel and a gearbox. The mechanical system has a long tradition throughout the 1900s, and applications based on it are widely produced today. Also see the articles Z-drive and L-drive.

As of April 2012, 230 Azipods had been installed on over 100 vessels in both single and multiple unit installations, with over 7 million hours of overall service.

One of the competing products of similar type is the Rolls-Royce Mermaid azimuth thruster. powering e.g. the cruiser Queen Mary 2. Most of the world's production of azimuthing propulsion systems is currently located in Finland with Rolls-Royce's factories in Rauma and ABB's in Helsinki.

The pod's propeller usually faces forward because in this puller (or tractor) configuration the propeller is more efficient due to operation in undisturbed flow. Because it can rotate around its mount axis, the pod can apply its thrust in any direction. Azimuth thrusters allow ships to be more maneuverable and enable them to travel backward nearly as efficiently as they can travel forward.

The podded design typically achieved a 9% better fuel efficiency than the conventional propulsion system when it was first installed in the 1990s. Improvements to the conventional design have shrunk the gap to 6%-8%, but on the other hand the hydrodynamic flow around the Azipod has been improved by fin retrofits and a dynamic computer optimization of the respective operating angles of the pods in multipod installations, yielding overall efficiency improvements now in the range of 18%.

The CRP (Contra-Rotating Propeller) Azipod places a contra-rotating azipod propeller behind a fixed propeller achieving improved fuel efficiency.

Concept

In the traditional azimuth propulsion system the motor is inside the ship's hull and the propeller is driven through shafts and gearboxes. In the Azipod system the electric motor is inside the pod, and the propeller is connected directly to the motor shaft. The AC motor of the pod is driven by electricity from the ship's generator by a cycloconverter. By avoiding the use of a traditional propeller shaft, the propeller can be further below the stern of the ship in a clear flow of water providing greater hydrodynamic and mechanical efficiency. The first vessel to feature the Azipod (1.5MW unit power) was the Seili, a waterway service vessel of the Finnish Maritime Administration with the installation in 1990. The vessel remains in use as of 2013, but her propulsion system has since been upgraded and the first Azipod ever installed on a ship is on display at the Forum Marinum maritime museum in Turku.

Electric power for the Azipod motor is conducted through slip rings that let the Azipod rotate through 360 degrees. Because fixed pitch propellers are used in Azipods, power for an Azipod system is always fed through a variable-frequency drive or cycloconverter that allows speed and direction control of the propulsion motors.

The fact that azimuthing pods can be reversed, and work equally well in both directions, has given gise to a new class of ships, the double acting ships, a concept developed by the Azipod's co-inventor Kvaerner Masa Yards in the 1990s. These typically have in one hull an ice-breaking function when sailing in one direction, and a conventional, e.g. tanker function, when sailing in the other direction. The Azipod is currently the only brand of podded propulsion that is ice-strengthened and certified for operations in ice by the relevant agencies, although an ice-strengthened version of the Mermaid pod is also offered by Rolls-Royce.^{[citation needed]}

Bearing-related problems while in use

While the smaller Azipod C design (up to 4.5MW power) seems to have been a largely trouble-free design, during the initial years in service some widely publicised cruise ship service disruptions with the bigger Azipod V design have occurred, see e.g. After the 2000 incident with the Carnival Paradise the root cause of the problems with the propeller shaft bearing was found and a modification programme was initiated for the fleet of Azipod Vs to take place during their scheduled drydocking, with very favourable results.

The latest design, the Azipod X, incorporates these improvements, with a view to a service interval of five years, and features bearings that can be taken apart and repaired from the inside of the pod while the ship is harboured normally. The latest major newbuilds featuring the Azipod XO are the two as yet unnamed 3,250 passenger vessels for the AIDA Cruises, the Celebrity Reflection (2012), the Norwegian Breakaway and the Norwegian Getaway

Meanwhile, the competing Rolls-Royce Mermaid pod seemed to suffer from recurrent reliability problems despite redesign efforts, resulting in prolonged legal battles that were settled in 2012.

External links

• The CRP Azipod Propulsion Concept Maritime Suppliers
• Article about use of azipod in semisubmersible rig
• ABB material including an illustration of the Azipod X/XO design (in Finnish)
• The Tale of the Mermaid Pods – Carnival Awarded $24 million in lawsuit with Rolls Royce