Vista "Sudden Stop"

[notscb]

It looks like the Vista had another incident of propulsion issues a few days ago. It must have been strange floating in the Gulf of Mexico and even reminiscent of the "poop" cruise (although that happened on a different class of ship). I'm wondering what recourse, if any, Carnival has against the ship builder/engine builder based on the seemingly regular issues with the vista class ships and what it might have been like onboard during this.

[ProgRockCruiser]

Can any of our resident propulsion experts help explain why there is a seemingly "unfixable" issue here that appears to just get bandaged up and sent out to battle again? 

 

@chengkp75 maybe?

 

What is it about the design?  In the article I link below (from 2019), the main culprit in past has been bearings failing.  Is this more a factor of poor design, poor manufacturing, overly-confident maintenance scheduling, or ... ?

 

To quote:

 

But the problem over the years has been that the bearings don't hold up. In 2010, Royal Caribbean Cruises Ltd. was awarded $65 million in a settlement in a suit against Rolls-Royce, in which it  alleged that the Mermaids installed on Celebrity Cruises' Millennium-class ships were flawed.

 

https://www.travelweekly.com/Cruise-Travel/Insights/Vista-just-latest-example-of-azipod-blues

 

And here's the ancient press release about the lawsuit Carnival won back in 2001:

 

https://www.carnivalcorp.com/news-releases/news-release-details/carnival-corporation-and-abb-reach-settlement-azipodr-propulsion/

[chengkp75]

Okay, one thing that folks need to understand about "podded propulsion systems" like Mermaids and Azipods, is that even though they have been around for 20+ years, that is still a "new" technology in shipbuilding.  There are about 2-300 "azipods" installed on all kinds of vessels worldwide (so, say, about 6000 "unit-years" of maintenance data).  This is a drop in the bucket compared to the (currently) 120,000 merchant ships with shafted propellers, that have operated for over 100 years (or over 1 million "unit-years").  So, reliability data is still being generated, and the technology constantly updated, so that each overhaul reflects the latest technology, but long term reliability data is still in its infancy.

 

Yes, the biggest problem with azipods is bearing design.  The large units on cruise ships were upscaled from smaller units previously fitted on ferries and ice breakers.  There was no historical data on bearing performance on these much larger units, and so the manufacturers take data from each failure, and each overhaul, to determine what needs to be improved to improve bearing performance.  While the power in each azipod has increased, the size does not, so the bearing has to take more loading on the same area, increasing the probability of wear earlier.  This is another major problem with azipods, the physical size is limited, while thrust bearings for shafted propeller, which are inside the ship, have no such size limitation, and can therefore be designed with minimum loading.  Remember, the thrust bearing of an azipod takes the entire force needed to push a ship like Oasis (which weighs about 100,000 metric tons) through the water, and the bearing area is only a few square feet.  This bearing takes all the propulsive force generated by the propeller, and transmits it to the hull, to push the hull.

 

Now, the other thing is that without knowing what the problems the Vista is having, saying that it has "propulsion issues" is like saying your car has "car issues".  Azipods are complex systems, and failure of any part could cause the entire unit to stop operating, or need to be shut down because it is causing instability in steering and vibrations, like the Freedom  (IIRC)had a few weeks ago in Europe.  This appeared to be a problem with the azimuthing system, not the motor/propeller, so this is totally different from earlier failures.  Could each of the Vista's propulsion problems be the same or different failures, so knowing whether they are "bandaged" and sent out again, or whether they are like a brake failure and a check engine light on your car, is unknown to anyone outside Carnival.

[ProgRockCruiser]

2 hours ago, chengkp75 said:

Okay, one thing that folks need to understand about "podded propulsion systems" like Mermaids and Azipods

chopped for brevity.

 

Thanks for the explanation.  Indeed, it does make sense that the usage on such large vessels, upscaling from ferries etc as you noted, is pushing the design of the mechanicals to their limits.

 

One therefore wonders whether the XL class of ships will have learned form those mistakes and be more reliable, or whether in a year or three we'll be hearing about "propulsion problems" on the Mardi Gras.

 

I was hope you (or someone else) "knows" that it is always the same thing going wrong - like how mid-1900s British cars always ended up with electrical problems...

 

But I guess with it being (relatively) new tech, when you fix one thing the next weakest link in the chain snaps.

[chengkp75]

46 minutes ago, ProgRockCruiser said:

One therefore wonders whether the XL class of ships will have learned form those mistakes and be more reliable, or whether in a year or three we'll be hearing about "propulsion problems" on the Mardi Gras.

I wouldn't  say there were "mistakes", just unforeseen design problems.  Remember, it is very difficult to simulate 100,000 tons of force on a bearing surface in the design shop, so most data and experience is "anecdotal", gathered in the field from actual usage of the units.  I would say that every year, at a minimum, there are upgrades to bearing metallurgy and design that are incorporated into bearings that are sent to the field, but again, the ship becomes the "test bed".  I know that RCI has determined that the thrust bearings on the pods for the Oasis class ships currently will not last a full 5 years between dry dockings, so they have started having "mini" dockings to just renew the azipod "cartridge" (shaft, bearings, seal) at around the 3 year mark.  The "cartridges" for all azipods are sent back to ABB for overhaul, so the manufacturer gets to see the parts taken out of service, knowing how long they were in service, and with operational data from the ship, to give them data points for further improvements.

 

54 minutes ago, ProgRockCruiser said:

I was hope you (or someone else) "knows" that it is always the same thing going wrong - like how mid-1900s British cars always ended up with electrical problems...

While bearing failure is the most common failure, some are bent blades, some are shaft seals, some are motor failures, some are azimuthing system failures, including the brakes, and some are to do with the electrical supply to the azipod motor, which must go through an inverter drive (which changes AC power to DC power and back to AC power) to allow the motor to operate at varying speeds, and these inverters are totally within the ship, but without them, the entire azipod is just a hunk of metal hanging under the ship.