Pods, pods,pods...

[SailorJeff66]

Seems to be a growing trend across all the lines. Azipod issues affecting max speed. Two of Royal's Oasis class(Oasis ended up with a crane on top of her for their trouble), now Carnival is losing Vista for almost a month. From what I gather, these are all ABB units, but I seem to recall the lines had issues with Rolls Royce units a few years back. Hopefully ChengKP can weigh in on this. In the U.S.N., when a common component exhibited reliability issues, an inspection fleetwide was initiated. Understanding the cost/schedule impacts a program would entail, compared to lost revenue from missed cruises and cancellation it seems they would almost have to do it. Thoughts?

[chengkp75]

5 hours ago, SailorJeff66 said:

Seems to be a growing trend across all the lines. Azipod issues affecting max speed. Two of Royal's Oasis class(Oasis ended up with a crane on top of her for their trouble), now Carnival is losing Vista for almost a month. From what I gather, these are all ABB units, but I seem to recall the lines had issues with Rolls Royce units a few years back. Hopefully ChengKP can weigh in on this. In the U.S.N., when a common component exhibited reliability issues, an inspection fleetwide was initiated. Understanding the cost/schedule impacts a program would entail, compared to lost revenue from missed cruises and cancellation it seems they would almost have to do it. Thoughts?

The problem with azipods is that while CC members think they are universal, they still represent a very small sample size of ship's propulsion systems, so useful historical data for units of the size used on cruise ships is still being generated.  One reason that Oasis was in the Freeport drydock was not due to any problem with pods, but with preventative maintenance that said that based on their fleet and ABB's worldwide experience, the pods would likely fail before the scheduled drydock in the fall.  So, this is a case of ongoing developmental planned maintenance.  And until the sample size gets larger, or there is more data (same sample size, but more years of usage), more accurate maintenance cannot be determined.  Marine engineering has, to me, always been a balancing act between cost and reliability.  You can have 100% reliability if you are willing to pay enormously for more frequent maintenance than the manufacturer recommends, or you can have minimized cost but will have some down time.  It is finding that "sweet spot" balance between the two that drives engineering in a profit oriented industry.

 

And, again, I don't know what the issue is with Vista's propulsion, so I can't say if this is an endemic problem or not.  Much complicated machinery and systems are lumped into "azipods" or "propulsion issues" here on CC, and even ships that have multiple problems with propulsion may not be experiencing repetitive failures, but failures of different components or systems at different times.  Even older propulsion systems like the shafted propellers on Caribbean Princess have large, complicated failures that require long periods of reduced power until an out of service period can be booked.

[buckeye rob]

42 minutes ago, chengkp75 said:

The problem with azipods is that while CC members think they are universal, they still represent a very small sample size of ship's propulsion systems, so useful historical data for units of the size used on cruise ships is still being generated.  One reason that Oasis was in the Freeport drydock was not due to any problem with pods, but with preventative maintenance that said that based on their fleet and ABB's worldwide experience, the pods would likely fail before the scheduled drydock in the fall.  So, this is a case of ongoing developmental planned maintenance.  And until the sample size gets larger, or there is more data (same sample size, but more years of usage), more accurate maintenance cannot be determined.  Marine engineering has, to me, always been a balancing act between cost and reliability.  You can have 100% reliability if you are willing to pay enormously for more frequent maintenance than the manufacturer recommends, or you can have minimized cost but will have some down time.  It is finding that "sweet spot" balance between the two that drives engineering in a profit oriented industry.

 

And, again, I don't know what the issue is with Vista's propulsion, so I can't say if this is an endemic problem or not.  Much complicated machinery and systems are lumped into "azipods" or "propulsion issues" here on CC, and even ships that have multiple problems with propulsion may not be experiencing repetitive failures, but failures of different components or systems at different times.  Even older propulsion systems like the shafted propellers on Caribbean Princess have large, complicated failures that require long periods of reduced power until an out of service period can be booked.

Thanks Chengkp75.  Always nice to hear of your educated, practical assessment of so many nautical topics.  Just for conversation... we are leaving on Allure September 8 and have heard, been notified of propulsion issues affecting a small amount  of the itinerary schedule.  I believe it is the starboard azipod that is out of commission.  I have not heard much unless  I totally missed it on how long until repairs will be made.  Will another azipod failure totally cripple the ship ?  Just wondering what is involved to repair and with the Nassau facilities down will any repairs have to made across the pond.  Wondering if our September 8 sailing will have diminished chances of happening.   Regards, Gerry.   

Edited June 25, 2019 by buckeye rob
left word out

[chengkp75]

Well, again, not sure what the failure is on Allure, whether it requires a drydock or not.  No, another complete failure of an azipod would not cripple the ship completely, but it would surely slow it down some.  95% of the ships traversing the world's oceans only have one propeller, so having one azipod working is fine.  Many of the smaller ships that have only two pods have operated for months or a couple years on one pod.  What would happen is that with only one working pod, there is no redundancy in steering, so many ports, all US ports for example, will require tugs to escort the ship all the way from the sea buoy to the dock, in case that last steering system were to fail.  One of Carnival's ships based out of New Orleans had a pod issue, and they were required to have a tug all the way up the river.

 

If the repairs to the pods require time out of the water (thrust bearing replacement, or far less common a problem with the motor itself), then yes it will need to go to Europe to find a drydock capable of handling Allure.  But there are many other systems that can affect whether an azipod works or not that don't require opening it up out of the water (a failure of the power inverters that drive the electric motor would be a prime example).  The ship generates power at 60Hz (just like the US), and therefore electric motors will only run at various fixed speeds based on this frequency.  To get a propulsion motor to run at varying speeds (to allow the ship to vary its speed), you need to take that AC power, convert it to DC power, and then convert it back to AC power with variable frequency using power semi-conductors (thyristors).  A failure of the power inverter (which is completely inside the ship) could cause a pod to be out of service without requiring a drydocking.

[dkjretired]

Celebrity has a long history of Pod problems going back to the launch of their M class ships around 2000. There have been multiple breakdowns shortened and cancelled cruises.  They even had a lawsuit I believe against Rolls Royce which  they won.

 

Recently they seem to have things under control and as always thank you Chang for your educated response.

Edited June 25, 2019 by dkjretired

[Mike981]

9 minutes ago, dkjretired said:

Celebrity has a long history of Pod problems going back to the launch of their M class ships around 2000. There have been multiple breakdowns shortened and cancelled cruises.  They even had a lawsuit I believe against Rolls Royce which  they won.

 

You know, you just reminded me of our Millennium cruise back around that time. It was very new and there were some Pod issues. Actually there were other issues as well, like running water coming through the ceiling at one of the bars. I can't remember the others at this time.

[SailorJeff66]

ChengKP, an article I just read said Vista's pod issues stemmed from a bearing. Makes sense, bearing issues cause excessive vibration at best, significant damage at worst. Allure is speed restricted due to pod issues, but I haven't seen specifically what the problem is. The article also said that Oasis was fixing pod issues at Grand Bahama when the dry dock crane fell on it. 

Interestingly, USN ships I've been on with traditional fixed propulsion have been able to affect repairs in water. Even had main shaft seals replaced. I imagine it's considerably more involved and difficult.

[MBP&O2/O]

I find the development of this technology fascinating. All of the ships I sailed on were single engine and single screw. Most had hydrodynamic characteristics similar to a house brick.  Bow thrusters were only on Star Trek!

Going alongside was a final broadside approach at 1 metre per minute, with tug assistance.

I don’t recollect ‘serious’ stern gland repairs without going into a dry dock ... but it was a long time ago.

It will be interesting to see what comes out of this and if any long term issues are examined.

[chengkp75]

6 hours ago, SailorJeff66 said:

ChengKP, an article I just read said Vista's pod issues stemmed from a bearing. Makes sense, bearing issues cause excessive vibration at best, significant damage at worst. Allure is speed restricted due to pod issues, but I haven't seen specifically what the problem is. The article also said that Oasis was fixing pod issues at Grand Bahama when the dry dock crane fell on it. 

Interestingly, USN ships I've been on with traditional fixed propulsion have been able to affect repairs in water. Even had main shaft seals replaced. I imagine it's considerably more involved and difficult.

Replacing shaft seals in water is a fairly common practice.  I've even done it on a stern thruster, where the propeller has to be removed to remove the seal cartridge, and we sailed around Hawaii for a week with the propeller and bits chained back in the tunnel at night while underway, and the divers would get back to work each day in port.  The gearbox oil was pumped out at the start, it remained full of sea water during repairs, and we then displaced the sea water with oil when repairs were completed.

 

The azipod has three bearings that support the rotating motor shaft.  Two are large ball/roller bearings that support the shaft and take the radial load of the motor, and these, being ball/roller bearings are not new technology, so don't present problems.  The third bearing is the thrust bearing, that transmits the entire 20Mw (26,000 hp) of thrust from the propeller through the motor shaft to the pod housing and then to the ship to move it.  These axial bearings are white metal bearings, and while this type of bearing is not new to the maritime industry, what is new is making a bearing of this power rating in as small a size as to fit into the azipod housing (load/area rating is much higher).  Therefore, as the power of azipods has increased (they were first used on icebreakers and tugs), new designs and new metallurgy has been developed to achieve the necessary load/area capability.  This has not been achieved yet, and maybe never will, to the degree of longevity that more conventional thrust bearings are capable of.  A large container ship may have a single slow speed diesel engine for propulsion, direct coupled to the propeller shaft, and capable of putting out 109,000 hp (81Mw, or more propulsion power than all three of Oasis' pods together), and the single thrust bearing in that engine is typically considered to have a life expectancy well over 20 years.

 

And, no, Oasis did not have a pod issue, it was a preventative replacement of the azipod cartridges that had been scheduled for months, and needed to be done prior to her scheduled drydock in the fall.  This kind of maintenance/repair consists of removing the propeller, and the thrust bearing "cartridge", which consists of the shaft seal, thrust bearing and a stub shaft, with a reconditioned spare.  ABB then reconditions the removed cartridges for the next ship to use.

[chengkp75]

5 hours ago, MBP&O2/O said:

I find the development of this technology fascinating. All of the ships I sailed on were single engine and single screw. Most had hydrodynamic characteristics similar to a house brick.  Bow thrusters were only on Star Trek!

Going alongside was a final broadside approach at 1 metre per minute, with tug assistance.

I don’t recollect ‘serious’ stern gland repairs without going into a dry dock ... but it was a long time ago.

It will be interesting to see what comes out of this and if any long term issues are examined.

I've done underwater stern seal repairs as noted, and times where we've tipped the ship down by the bow to get the shaft seal above the water for repairs.  This is more typical, since the rubber seal rings have to be cut to fit around the shaft, and then re-vulcanized in place with an electric heating tool.

 

Basically, the cartridge will go to ABB, they will disassemble the thrust bearing and do failure analysis on it and it's metallurgy, and add this to their database for future decisions on design changes or maintenance intervals.  Typically, this is not a total bearing failure, but the bearing has imbedded temperature sensors, and the oil system has metal particle detectors, and the filters have clogging indicators, and when any of these start to go out of optimal range, they will stop using the pod to prevent further damage.

[MBP&O2/O]

“I've done underwater stern seal repairs as noted, and times where we've tipped the ship down by the bow to get the shaft seal above the water for repairs.”

 

My speciality was pointing them in the right direction .... what went on in the ER was too much for my brain 😀 I do know that when a main condenser pipe goes ‘pop’ , with a 38 foot draft,  it causes major problems 🚣‍♀️

[chengkp75]

1 hour ago, MBP&O2/O said:

“I've done underwater stern seal repairs as noted, and times where we've tipped the ship down by the bow to get the shaft seal above the water for repairs.”

 

My speciality was pointing them in the right direction .... what went on in the ER was too much for my brain 😀 I do know that when a main condenser pipe goes ‘pop’ , with a 38 foot draft,  it causes major problems 🚣‍♀️

Nah, you just get your sheet metal and bailing wire and get your Saturday night salt water shower a few days early.

[SRF]

1 hour ago, chengkp75 said:

Nah, you just get your sheet metal and bailing wire and get your Saturday night salt water shower a few days early.

 

You forgot the duct tape. 😄

 

[Heidi13]

11 hours ago, MBP&O2/O said:

I find the development of this technology fascinating. All of the ships I sailed on were single engine and single screw. Most had hydrodynamic characteristics similar to a house brick.  Bow thrusters were only on Star Trek!

Going alongside was a final broadside approach at 1 metre per minute, with tug assistance.

I don’t recollect ‘serious’ stern gland repairs without going into a dry dock ... but it was a long time ago.

It will be interesting to see what comes out of this and if any long term issues are examined.

Vaguely remember those days of single fixed pitch, but haven't sailed on them since I was a cadet.

 

Our dockings were a little faster, for a bow landing our initial reduction from 20 kts was at 1 mile out and we were docked in 7 minutes. Stern landings only took about an extra minute, with Becker rudders & 2 bow thrusters.

 

For about the past 10 years we have completed most underwater repairs using local divers. They routinely changed out entire bow thrusters at night, taking 2 or 3 nights, so as not to disrupt the daily sailings. They have also changed blades on our CP props. Many years ago I lost the flap on the Becker rudders, divers added a temporary patch to balance the leading/trailing edges, then installed a new flap when received. For hull repairs they used a cofferdam and completed underwater welding.

 

Only emergency drydocking I recall was for shaft repairs, as they had to pull the shaft, everything else completed by divers.

[MBP&O2/O]

“You forgot the duct tape”

True .... but the ‘pop’ took out the top half of the pipe for a length of - it was guestimated - about 15 inch ...... so the tape was too small 😀

I was told the ‘shower’ was something to behold .... shampoo was not supplied but brown trousers were 😳

[AL3XCruise]

15 hours ago, chengkp75 said:

The azipod has three bearings that support the rotating motor shaft.  Two are large ball/roller bearings that support the shaft and take the radial load of the motor, and these, being ball/roller bearings are not new technology, so don't present problems.  The third bearing is the thrust bearing, that transmits the entire 20Mw (26,000 hp) of thrust from the propeller through the motor shaft to the pod housing and then to the ship to move it.  These axial bearings are white metal bearings, and while this type of bearing is not new to the maritime industry, what is new is making a bearing of this power rating in as small a size as to fit into the azipod housing (load/area rating is much higher). 

 

Thank you for the explanation.  I've read many article talking about bearing issues, but that is the clearest, most concise explanation as to the unique challenges of azipod bearings.

 

Are thrust bearings on shafted ships generally accessible from within the hull?

[SailorJeff66]

My marine engineering experience comes from the "grey funnel line".  First ship was a carrier with 4 fixed pitched screws running off boilers. I also served on more modern ships with Controlled Pitch Propellers and APU's. Modern cruise ships are truly marvels of engineering. I'm up for the all access tour on my next cruise but sadly, My idea of "all access" probably won't match what's offered. 

[SailorJeff66]

2 hours ago, AL3XCruise said:

 

Thank you for the explanation.  I've read many article talking about bearing issues, but that is the clearest, most concise explanation as to the unique challenges of azipod bearings.

 

Are thrust bearings on shafted ships generally accessible from within the hull?

On USN ships, there is an inflatable stern tube seal that acts as a backup to the normal stern tube seal. I have been on a couple ships where they used divers to remove the thrust bearing and shaft seal. Commercial vessels? No idea. 

[chengkp75]

8 hours ago, AL3XCruise said:

 

Thank you for the explanation.  I've read many article talking about bearing issues, but that is the clearest, most concise explanation as to the unique challenges of azipod bearings.

 

Are thrust bearings on shafted ships generally accessible from within the hull?

For a diesel electric ship, the thrust bearing is directly behind the electric propulsion motor inside the ship.  For a direct coupled diesel that most cargo ships have, the thrust bearing is part of the engine, and is accessible from inside the engine, since the engine is 4 stories tall.