The Azipod...in all its glory...

This is a long but informative description of everything about the dreaded Azipod that so many have come to hate...especially when ports are missed.

In the wake of the introduction of azipod propulsion systems on cruise liners lies the wave of the future. Combining the propulsion and steering of conventional ships, an azipod system replaces traditional propellers and lengthy drive shafts and rudders used for more than a century on oceangoing vessels.

 

Eight cruise lines--Carnival, Celebrity, Crystal, Cunard, Holland America, Mediterranean Shipping, Norwegian, and Royal Caribbean--have a total of 12 azipod-propelled ships in service as of 2001; 17 others are being planned or under construction.

 

The reliability and effectiveness of azipod propulsion has been proven over the last decade in the toughest ocean-going ship applications--Arctic tankers and ice breakers. In those non-passenger-carrying vessels, propulsion was provided by only one azipod; cruise ships have two for additional maneuverability and redundancy.

 

Each of the two azipods on passenger ships has a fixed-pitch propeller at the front to move the ship through the water. The azipods are suspended beneath the water line at the aft end of the ship. There's one azipod on the port and another on the starboard side. Each azipod is mounted on a shaft perpendicular to the center line of the ship's hull.

 

The shaft can be rotated to any position in 360 degrees. The angular position of rotation can change the direction of the ship's movement or keep it sailing straight ahead. Thus, ships with azipods are steered without a rudder, similarly as small boats use an outboard motor for power and steering (but with their rear-mounted propellers, outboards "push" their vessels, while azipods, with forward-mounted propellers, "pull" their vessels). The positioning of the azipods and the speed of their motors are determined by officers on the bridge.

 

This system integrating power and rotation into one unit was begging for a shorter, simpler descriptor. The resultant acronym "azipod" incorporates azimuth (distance in angular degrees measured clockwise from a standard direction) and pod (a streamlined compartment). Thus, an azimuthing, podded unit was shortened to azipod.

 

Cruise passengers needn't have concerns about safety when sailing on the newest ships with azipod propulsion systems. Azipods offer safer cruising in harsh weather and greater control in restricted passages. For instance, azipods are capable of moving the ship backwards during docking. The pods can be rotated to the 180-degree position, or they can be positioned straight ahead (O-degree position) while the motors are reversed. Each azipod can be operated independently of the other allowing subtle maneuvering. There's a lot of flexibility.

 

Also, during docking procedures the azipods can be rotated to the 90-degree or 270-degree position to move the ship to the side. In order for ships constructed in the latter part of the last century to move sideways, they needed thrusters built into the bow and the stern--or tugboats. A thruster is a separate motor system with propellers concealed within the hull that moves water to the side of the ship, thus moving the ship in the opposite direction. (Remembering our basic physics, "every action has an equal and opposite reaction.") Ships with azipods do not need a separate stern-thruster system; however, bow thrusters are still required.

 

Royal Caribbean's Voyager Class ships have azipods port and starboard as previously described, plus a third, central stationary pod for additional power when cruising. To date, the biggest installation planned is for Cunard Line's Queen Mary 2, which is scheduled to debut in late 2003. She will be the largest ocean liner ever built and the first with a four-pod installation--two fixed pods and two azipods. The Queen Mary 2 plans to have a maximum speed of 30 knots, which will be helpful in establishing a regular trans-Atlantic schedule of crossings, even in midwinter's stormy weather.

 

By looking at the photos accompanying this article, it's hard to know exactly what's inside the azipods. The azipods do not have engines inside, but instead have huge variable-frequency electric motors. The power plant providing the electricity to the motors is located in the hull of the ship. This power-generation system also provides electricity to support all the ship's other electrical needs.

 

Thus azipod ships are, basically, electrical vessels, from lighting and air-conditioning to cooking, dish-washing, laundry, and all the other creature comforts we expect. From the generation of freshwater to the processing of waste materials, the ship is an electrically operated, self-contained, ecologically correct community. The power needed just to drive the azipods on Carnival's 77,367-gross-register-ton Elation is as much as 28 megawatts--that's equal to 280,000 100-watt light bulbs!

 

The power plant's engines that drive the electric generators on today's azipod-propelled cruise liners are of two basic types: diesel and turbine. Diesel engines operate on the same principles used in cars and trucks. Turbine engines are similar in design to those on jet airplanes.

 

One of the many criteria that the cruise lines considered in choosing the engine type was the environmental impact of the exhaust smoke from ship funnels. Environmentally friendly, smokeless power-generation systems release no soot or visible smoke. Smokeless engines for the power-generation system would be ideal. Royal Caribbean's Radiance Class and Celebrity's Millennium Class ships have advanced-design turbine engines that approach this smokeless goal, partly by using a more refined, cleaner-burning fuel. Carnival has taken a different tact, developing smokeless diesel engines called EnviroEngines. These newest ships from Royal Caribbean, Celebrity, and Carnival are probably the most environmentally friendly cruise liners sailing today. Planet watchers should be pleased.

 

Another advantage of the azipod system is increased fuel efficiency, which, according to Holland America, allows its 61,000-grt Amsterdam to save "up to 40 tons of fuel per week." This is primarily due to the overall improved efficiency of the azipods. In classic installations, where propellers are attached to drive shafts, the rotating shafts set up a swirl in the water preceding the propellers--a situation analogous to sailing upstream. The arrangement of the azipods with their front propellers working in water not distributed by shaft lines is more like a ship sailing on a lake. Another way the azipod-propelled ship achieves greater fuel efficiency is through the use of the latest materials--many stronger and lighter in weight than were used in construction in an earlier era.

 

Also, ships with azipod systems have higher cruising speeds, not always concurrent with fuel conservation, which may result in more or longer port calls. This also allows some lines to have itineraries with ports at greater distances from each other. Norwegian Cruise Line's Norwegian Star provides year-round Hawaii service with a visit to Fanning Island, Republic of Kiribati, about 600 miles from Hawaii, for a day at the beach. Traveling at about 25 knots, the Norwegian Star covers the distance in just 24 hours, giving passengers two sea days--and a remote island call--on a seven-day cruise.

 

Initial inferences by the cruise lines that there would be space savings with the new azipod system have not materialized in passenger areas. When queried, Carnival public relations personnel responded, "Please be advised that we didn't actually `save' space; the space is used for other purposes, such as a second incinerator. A parallel benefit was the reduction in mechanical equipment. Azipods allow us to delete shafts, shaft bearings, rudders, thrusters, and associated equipment, which reduces maintenance and improves efficiency."

 

Engineers report that azipod systems have quieter power plants than those of the last generation. Their electrical power generators, although within the hull, are more vibration free than former installations, resulting in a quieter ship. Acoustic design using sound insulation helps further reduce any power-plant and propulsion-system noise, improving in-cabin passenger comfort. Onboard noise also is lower because azipod propulsion motors are mounted outside the ship's hull.

 

Of the cruise lines with azipod-propelled ships, Royal Caribbean International has the most, with seven ships using turbine-powered electrical-generating systems. Its Voyager of the Seas came into service in 1999, followed by Explorer of the Seas (2000), Adventure of the Seas (2001), and Radiance of the Seas (2001). Still in construction and planned to be launched are Brilliance of the Seas (2002), Serenade of the Seas (2003), and Jewel of the Seas (2004). (Note: Voyager, Explorer, and Adventure of the Seas have a third, central fixed pod.)

 

Holland America Line has six ships powered by diesel-electric generators and azipods. Only one, the Amsterdam (2000), is sailing presently. Planned for service later in 2002 is the Zuiderdam, to be followed by the Oosterdam (2003), and three more Vista Class sisters in 2004 and 2005.

 

Carnival Cruise Lines has five ships with azipods with power generation by diesel EnviroEngines. Now in service are the Elation (1998), Paradise (1998), Carnival Spirit (2001), and Carnival Pride (2002). The Carnival Legend will be christened later in 2002.

 

Celebrity Cruises has four azipod-propelled ships with turbine-powered electricalgenerating systems. Three of them are already in service: Millennium (2000), Infinity (2001), and Summit (2001). The Constellation will enter service in mid 2002.

 

Other lines with azipod propulsion and diesel-powered electrical-generating systems include: Crystal Cruises' Crystal Serenity (2003); Mediterranean Shipping Cruises' MSC Symphony (2003) and MSC Harmony (2004); and Norwegian Cruise Line's Norwegian Star (2001) and Norwegian Dawn (2002). Cunard Line's Queen Mary 2 (2003) has both azipods and fixed pods, with both diesel and turbine electric-power generators, and is scheduled to enter service in 2003. Cunard is planning another large ship with azipods, yet unnamed, for a debut in 2005.

 

Most cruise passengers sailing on these technologically advanced, azipod-propelled ships will not know anything about the "motors," probably won't notice any differences in onboard background noise level, and may not care one iota about propulsion systems--even though their cruise will be smoother and safer. And although this writer has found this to be a fascinating subject, a ship with an azipod propulsion system is probably not an important reason to take a cruise!

Aside from being a dated news release ) by a couple of years, it fails to discuss the major problem with the azipod system - thrust bearings.

The bearings are flawed in that they seemingly can't take the forces/pressures they are under - good engineering will eventually overcome it - but until then, they are subject to failure and are unreliable.