Z-drive Vs Azipod
Angelique Syria
ABB released this video today that gives a new look at their Azipod ship propulsion systems that they are successfully integrating on board a number of different vessels including icebreakers, offshore supply vessels, and in particular, cruise ships. Azipods differ from conventional shaft or z-drive configurations in that they are exclusively powered by high voltage electricity and the motors that turn the propeller are located outside the hull and integrated directly with the propeller itself.
ABB will supply complete electrical systems for both ships; including generators, and transformers for propulsion, engine room and distribution, frequency converters, bow thruster motors, and other related power system equipment, as well as its latest generation Azipod XO propulsion systems.
I prefer to use marinetraffic dot com.... It shows all vessels in an area that broadcast (Automatic Identification System) AIS data. Most all commercial, and many pleasure craft use AIS to keep track of other traffic around them.
I have had really bad experiences with ABB equipment and their poor quality. The Electrify America ABB chargers have horrendous quality issues to say the least. Lucky if 1 out of 4 chargers are working at any site and then that 1 charger will only produce 20% or less of the power it's suppose to. With complex clutches and complex planetary gears in the Azipod's I'm not sure I would rule an issue here out.
Historically, the azimuthing system (the only system with clutches and planetary gears) have not been an area of failure. And, the technology for these azimuthing systems is far more established than the azipod itself, being used a decade before azipods were invented in azimuthing thrusters and z-drives.
And, the ABB group is a huge conglomerate that covers many industries, so poor quality control in one area does not translate into poor quality in another, as each industry is a separate corporate entity, many times, as in the Marine division, having purchased other companies to integrate those companies' products into their own line.
It is hard to say w/o being there and being hands-on. But I can say on smaller scale systems when the propeller, impeller, or other device connected to the motor has impacted solid mass it unfortunately reverberated through the ancillary connections wiping out the gears and clutches. I thought I could fix it but ended up scrapping it in the end because for me it was beyond my skills and scope to get everything solidly connected to function under stress/load even though at idle it would function ok.
On quality I respectively disagree - it's a corporate culture - Six Sigma Quality, Malcom Baldridge Corporation awards, ect. ABB has serious issues, change the corporate culture, win a Baldridge type award and I will be a believer too.
The propeller of an azipod has no gearing or clutches. The propeller is mounted to the shaft, which is also the motor shaft. The propeller and motor turn in a 1:1 ratio. There are two radial ball/roller bearings, and an axial tilting pad type thrust bearing.
The only gearing is that the pod itself has a large ring gear, and there are two motors that drive small pinion gears to turn the ring gear and the pod. There are friction clutches that will slip and prevent damage to the azimuthing motors when the pod is prevented from turning.
For nearly all large ocean-going vessels these days, of whatever type (container, tanker, cruise ship), or whatever propulsion means, there are no clutches or gearing between the propeller and the propulsive means (electric motor, diesel engine). LNG ships are about the only large ships that use steam turbines that need gearing to the propeller.
The various sized 700+ azipods in service have provided over 20 million operating hours to date. While I feel that in the marine industry, ABB provides a world class service, based on my years of experience with them, I can't, and shouldn't, extend that approval to something I have no knowledge of, like EV charging stations, nor should criticism go the other way.
The diesel engines are maintained in a "standby" mode, so that if either the automation says it needs to start another generator due to an alarm, or the duty engineer pushes the button to start the engine to get ready to leave port, the engine will go from a standstill to full speed, synchronise itself online and be able to generate full power within about 45 seconds.
The azipods are not in standby, and will have some automated sequences like running the oil pumps for a minute before starting the motor, and the frequency drive needs to be up and online before the motor can be started, but it's about 2 minutes.
No, the big advantage to diesel electric propulsion is that the diesel generators can be used for anything. They all feed the same switchboard, which powers everything on the ship; propulsion, hotel load, engineering hotel load. Therefore, you can fine tailor the power capacity on line to the power demand more closely than if you only had generators for hotel load, and diesels for propulsion. This saves fuel.
The electric drive motors used on cruise ships, whether for azipods or for shafted propellers, need a frequency converter to operate. Since an AC motor operates at the frequency of the power (typically 60 Hz), it will only operate at one speed. The frequency converter takes the AC power, converts it to DC power, and then converts it back to AC power at the right frequency to drive the motor at the desired speed.
That would depend on how far down you've taken the engine. If you are doing maintenance on the engine, then it could take days to get the engine back to running. But, virtually every ship keeps all their generators in standby (unless being worked on), because the automation will sense an alarm or failure of a generator online, and automatically start another to replace it. So, "standby" is the normal condition of a diesel generator. The cooling water is kept close to operating temperature, the lube oil is kept near operating temperature, and constantly circulated through centrifuges to remove contaminants, and fuel is circulated through the engine right up to the injectors, to keep the fuel from solidifying, so even if I just finished working on an engine, and wanted to test it, I could press the "start" button, and the lube oil pump would come on to pressurize the bearings, and the starter would engage in about 15 seconds. Once the engine is running at speed, it can provide full power immediately (it is not recommended, but is possible), and the process to synchronize the generator to the power bus is only a few seconds as well.
I guess the advantages of multiple generators connected to a central distribution system is not only redundancy but the ability to load shed non-essential services in an emergency? On the Boeing we have 3 generators, one powered by each engine and one powered by the auxiliary power unit. If we lose one of the main ones the aircraft load sheds galley power etc so that essential services are still powered while we start the spare, only takes a couple of minutes. I suppose you could argue on a cruise ship that the galley is an essential service though!!
Yes, there is load shedding capability, but on a cruise ship, the galley is such a small part of the load that it isn't included in load shedding. It only takes into account the largest loads, like AC, thrusters, and half of the propulsion power. But, to be honest, the only time I seen load shedding actually working is when we have to test it annually. Typically, a new generator is online before a failing one drops off (early warning alarms), so the plant never gets to the need to shed load.
We just got an update that repairs on continuing. Still plan to sail on 9/15. They will provide another update on Sunday. Really hoping they will sail as I am already in AK and booked my air home through RCL. ?
c80f0f1006