Azipod

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Closeup of one of USCGC Mackinaw's 3.3 MW Azipod units

Azipod is the registered brand name for ABB Group's range of electric podded propulsion units. Developed in Finland jointly by the shipbuilding company Masa-Yards and ABB, Azipod is a marine propulsion unit consisting of a fixed pitch propeller mounted on a steerable gondola ("pod") which also contains the electric motor driving the propeller.

Concept[edit]

In the traditional azimuth thrusters such as Z-drive and L-drive thrusters, the propeller is driven by an electric motor or a diesel engine inside the ship's hull. The propeller is coupled to the prime mover with shafts and bevel gears that allow rotating the propeller about a vertical axis. This type of propulsion system has a long tradition throughout the 1900s and today such propulsion units are produced by a number of companies around the world.[1]

In the Azipod unit, the electric motor is mounted inside the propulsion unit and the propeller is connected directly to the motor shaft.[2] 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, thereby providing greater hydrodynamic and mechanical efficiency. Furthermore, it increases flexibility in the general arrangement of the vessel's power plant.

Electric power for the propulsion motor is conducted through slip rings that let the Azipod unit rotate 360 degrees about the vertical axis. Because Azipod units utilize fixed-pitch propellers, power is always fed through a variable-frequency drive or cycloconverter that allows speed and direction control of the propulsion motors.

The pod's propeller usually faces forward because in this pulling (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%.[3]

History[edit]

Development[edit]

The first commercial Azipod unit, installed on the Finnish fairway support vessel Seili in 1990, is now displayed at the Forum Marinum maritime museum in Turku, Finland

In 1987, the Finnish National Board of Navigation made a co-operation proposal to the multinational electrical equipment corporation ABB Group and the Finnish shipbuilder Masa-Yards for the development of a new type of electric propulsion unit.[4] Prior to this, the companies had been working together for decades in the field of diesel-electric propulsion systems and in the 1980s produced the first icebreakers with alternating current propulsion motors and cycloconverters.[5]

The development of the prototype started in 1989 and the first unit was ready for installation in the following year.[6] The 1.5 MW unit, dubbed "Azipod" (a portmanteau of "azimuth thruster" and "podded propulsion unit") was installed on the 1979-built Finnish fairway support vessel Seili at Hietalahti shipyard in Helsinki, Finland. After the refit, the vessel's icebreaking performance was considerably increased and she was also found out to be capable of breaking ice astern (backwards). This discovery of a new operating mode eventually led to the development of the double acting ship concept in the early 1990s.[7][8] When Seili was refitted with new propulsion system in the 2000s, the prototype unit was donated to Forum Marinum and put on display in Turku, Finland.

Following the encouraging experiences from the prototype installation, the development of the Azipod concept continued and the next units were retrofitted on two Finnish oil tankers, Uikku and Lunni, in 1993 and 1994, respectively. Nearly eight times as powerful as the prototype, the 11.4 MW Azipod units considerable increased in the icegoing ability of the vessels that were already built with independent icebreaking capability in mind.[7] Since the 1990s, the vast majority of ships capable of operating in ice without icebreaker escort have been fitted with Azipod propulsion system.[9]

The first three Azipod units were of so-called "pushing" type in which the propeller is mounted behind the gondola. In the subsequent installations, ABB adopted the more efficient "pulling" configuration similar to propeller-driven airplanes.

Another breakthrough for the Azipod came when Carnival Cruise Lines chose Azipod propulsion for the last two ships of the eight-strong Fantasy class. The world's first cruise ship fitted with Azipod propulsion units, Elation, was delivered by Kværner Masa-Yards Helsinki shipyard in the spring of 1998.[10] Even though the Azipod was initially developed for icebreaking vessels, cruise ships have become the largest group of ships by type to be fitted with Azipod propulsion system since the 1990s and the success of the electric podded propulsion units has paved way for competitors such as Rolls-Royce's Mermaid. Among the vessels fitted with Azipod units are Royal Caribbean International's Voyager-, Freedom- and Oasis-class cruise ships, each of which has hold the title of the largest cruise ship in the world at the time of the delivery.[9]

In the early 2000s, ABB introduced a special type of propulsion system consisting of an Azipod unit mounted behind another propeller driven by a conventional shaftline. By operating in the rotating wake of the other propeller, the contra-rotating Azipod unit increases the vessel's hydrodynamic propulsion efficiency by about 10%.[11] As of 2014, the CRP Azipod propulsion system has been fitted to four high-speed ferries operated by Shin Nihonkai in Japan.[9]

Another further development of the original electric podded propulsion concept is the Compact Azipod, a smaller Azipod unit introduced in the early 2000s. It is intended for smaller ships such as research vessels and yachts as well as dynamically positioned drilling rigs that may utilize up to eight such propulsors.[9][12] The smaller Azipod Compact differs from the full-size unit by its permanent magnet synchronous motor which is directly cooled to sea water. For drilling vessels, it is also available in "pushing" configuration and can be fitted with a nozzle to increase bollard pull thrust in stationkeeping applications.[13] Unlike the full-sized Azipod units which are assembled in Finland, the Compact Azipod units are manufactured in China.[14]

Today, ABB is the largest manufacturer of electric podded propulsion systems with over 250 units delivered to over 100 ships and cumulative operating hours exceeding 7 million.[15] Following the success of the Azipod concept, "azipod" is sometimes used as a generic trademark for podded propulsion units even when referring to competiting products such as Queen Mary 2's Mermaid pods.[16] As of 2014, most of the world's production of azimuthing propulsion systems is located in Finland with Rolls-Royce and Steerprop producing Z-drive thrusters in Rauma and ABB having the Azipod manufacturing plant in Helsinki.[1]

Bearing-related problems[edit]

During the initial years in service, some widely publicised cruise ship service disruptions with the bigger Azipod V design have occurred, see e.g.[17] 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.[18]

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.[19][20] 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.[3][21]

Meanwhile, the competing Rolls-Royce Mermaid units seemed to suffer from recurrent reliability problems despite redesign efforts, resulting in prolonged legal battles that were settled in 2012.[22][23]

Notes[edit]

  1. ^ a b Tammiaho, Erkki. "Ruoripotkurilaitteiden liiketoiminta Suomessa, TEKES, 258/2009" (PDF) (in Finnish, illustrated). Retrieved 2013-12-05. 
  2. ^ Pakaste, Risto et al. (February 1999). "Experience with Azipod propulsion systems on board marine vessels" (PDF). Retrieved 2012-12-25. 
  3. ^ a b "Azipod propulsion drives take the next step". Skipsrevyen. March 2011. Retrieved 2013-09-24. 
  4. ^ Hepo-oja, Anssi; Mäki-Kuutti, Viktor (2012). Mekaanisen ja sähköisen propulsiojärjestelmän esittely. Satakunta University of Applied Sciences. 
  5. ^ Cycloconverters for the new icebreaker from Kymmene-Strömberg. Navigator 1985.
  6. ^ 1. Dynamosta Azipodiin - vuosikymmenien kokemukset jäänmurtajista. ABB Group. Retrieved on 2013-10-05.
  7. ^ a b Juurmaa, K et al.: The development of the new double acting ships for ice operation. Kvaerner Masa-Yards Arctic Technology, 2001 and 2002.
  8. ^ Juurmaa, K et al.: New ice breaking tanker concept for the arctic (DAT). Kvaerner Masa-Yards Arctic Technology, 1995.
  9. ^ a b c d References - Propulsion Products. ABB. Retrieved on 2014-04-26.
  10. ^ 6.11. Azipod ® propulsion. ABB. Retrieved on 2014-04-26.
  11. ^ The CRP Azipod Propulsion Concept. ABB. Retrieved on 2014-04-26.
  12. ^ Compact Azipod. ABB. Retrieved on 2014-04-26.
  13. ^ Azipod C. ABB. Retrieved on 2014-04-26.
  14. ^ ABB Propulsion Products for Main Propulsion and Thrusters. ABB, June 2012. Retrieved on 2014-04-26.
  15. ^ ABB Oy, Marine and Cranes. ABB. Retrieved on 2014-04-26.
  16. ^ Inside view: What makes QM2 go. Beyond Ships. Retrieved on 2014-04-26.
  17. ^ Fredrickson, Tom (2000-07-22). "Carnival's Paradise Coming To Yard For Repairs". Newport News, Virginia: Daily Press. Retrieved 2013-09-24. 
  18. ^ "Carnival Corporation And Abb Reach Settlement On Azipod® Propulsion System". Carnival Corporation. Retrieved 2013-09-24. 
  19. ^ http://www.wplgroup.com/aci/events-pdfs-eu/aci-industry-features-abb.pdf
  20. ^ "Propulsion Systems by ABB Marine". Wplgroup.com. 2012-02-13. Retrieved 2013-09-24. 
  21. ^ "AIDA newbuilds will use air bubbles and Azipods to cut fuel consumption". MarineLog. 2012-03-12. Retrieved 2013-09-24. 
  22. ^ "Bearing Failure Sidelines Cruise Ship Again". The eBearing News. 2005-03-28. Retrieved 2013-09-24. 
  23. ^ "Rolls-Royce Crystal Settle Mermaid Propulsion System Row". Law360.com. Retrieved 2013-09-24.