The Royal Navy Discussions and Updates

[Volkodav]

Just out of idle interest, is it cheaper to run all GT say smaller turbines for low load and larger kicking in when required? Surely there is less weight and less maintenance and less space required for GTs cf DGs. What is the rationale for having diesel? Sorry if I've missed something obvious.

Really not sure which is better although the use of GT generators of the Spruance class was given as one of the reasons for their very quiet operation and they were retained on the following Arleigh Burkes. Actually the latest Burkes have switched to electrically started GTGs over the previous pneumatically started ones, further reducing maintenance costs.

I believe the issue may be higher up front costs for the GTs, combined with conservatism buy designers, builders and users, for instance the RAN was apparently against the use of high pressure, direct injection diesels until recently, due to safety concerns, in particular following the atomised diesel fire on HMAS Westralia.

 

[StobieWan]

Just out of idle interest, is it cheaper to run all GT say smaller turbines for low load and larger kicking in when required? Surely there is less weight and less maintenance and less space required for GTs cf DGs. What is the rationale for having diesel? Sorry if I've missed something obvious.

Fuel consumption - most GT's have a fairly flat fuel consumption curve in that they use a lot of fuel running at full power and don't get *much* more economical on lower power settings - whereas diesels are very economical to use for generators if tuned to run at a low RPM range.

The Type 45 on the other hand has WR21 GT's which are much more economical to run at lower settings than conventional GT's, and this economy may have informed the design and spec of the rest of the propulsion arrangement.

I think people keep forgetting the Type 45 was a genuinely revolutionary design which on launch was about a generation ahead of anything else in the peer or near peer navies - the DDG 1000 program actually sent engineers to work on the Type 45 as they prepared to launch their first in class so they'd gain operational experience. It's definitely *not* a case of "Duh, BAE..they so stoopid.." - more a hangover from some very risky program elements with a lot of customer changes late during the design phase, which is always going to be risky and expensive.

IFEP is the mutts nuts for military work and it's a crying shame we're going to step away from it for the Type 26.

What I don't know right now is if the diesels are being replaced because they're unreliable or under spec - or both.

 

[John Fedup]

Modern Diesel engines (Warstila included) are very efficient and reliable. Dirty fuel is the most common failure reason. However, for good performance the load application must match the sweet spot rpm for the the diesel's rated power output for good performance. If the diesel is run at lower power for prolonged periods carbon build up will cause problems. In the case of the Type 45, it appears the diesels are too small for the generators resulting in the need for the diesels to be run at a higher than specified power which is also problematic. The bean counters saved some capital expense buying diesels with lower power ratings.

 

[The Ginge]

Modern Diesel engines (Warstila included) are very efficient and reliable. Dirty fuel is the most common failure reason. However, for good performance the load application must match the sweet spot rpm for the the diesel's rated power output for good performance. If the diesel is run at lower power for prolonged periods carbon build up will cause problems. In the case of the Type 45, it appears the diesels are too small for the generators resulting in the need for the diesels to be run at a higher than specified power which is also problematic. The bean counters saved some capital expense buying diesels with lower power ratings.

The problem is not with the Diesel engines Per Se. The problem is the Gas Turbines are unreliable, as evidenced by work already on most of them with blade renewals etc etc. They were at the time of installation the cutting edge of technology in this field so the T45's could run supper efficient. The problem is that the very complicated control mechanism shuts down the GT's dumping the full required load on the the diesel Driven Gen's.
At that point the control system sees the Diesel Driven sets are overloaded so closes those down as well. Hence the fairly instant "blackout" that occurs.
Now the problem is the ships were built around the GT's with no removal access to them. IE the GT's are effectively "sealed for life" in the ship.
The Diesel Gen Sets are accessable, so to stop the sudden shut down of the System when the GT's go out for any reason the refitt is to put in bigger more capable Diesel Gen Sets. So if a sudden load on to the diesel side occurs there is enough emergency capacity to slow the ship down, reduce the power demands in a controlled way so that the Diesel Gen can continue running the Ship whilst the GT's are brought back online.
The problem with the design is that really you want to rip out the GT's and put in the now more reliable available GT sets. But as that would involve effectively cutting the ships in Half it really is a bit of a last resort never done it, don't want to try it procedure.
So as a "fix" put in the bigger Diesel Gen Sets that at least gives you a decent chance at keeping going even if it is at 8 to 12 knots and fighting the ship whilst you engineers run around like blue a***d flies getting your main propolsion system back online.
So the core problem is the GT's as I understand it, not the Diesel side which if brought online in a controlled mannor do fine, but just can't deal with a big dump on them. You may argue that the original design should have had redundency built in, but you pays your money and takes your choice I suppose.

 

[John Fedup]

The problem is not with the Diesel engines Per Se. The problem is the Gas Turbines are unreliable, as evidenced by work already on most of them with blade renewals etc etc. They were at the time of installation the cutting edge of technology in this field so the T45's could run supper efficient. The problem is that the very complicated control mechanism shuts down the GT's dumping the full required load on the the diesel Driven Gen's.
At that point the control system sees the Diesel Driven sets are overloaded so closes those down as well. Hence the fairly instant "blackout" that occurs.
Now the problem is the ships were built around the GT's with no removal access to them. IE the GT's are effectively "sealed for life" in the ship.
The Diesel Gen Sets are accessable, so to stop the sudden shut down of the System when the GT's go out for any reason the refitt is to put in bigger more capable Diesel Gen Sets. So if a sudden load on to the diesel side occurs there is enough emergency capacity to slow the ship down, reduce the power demands in a controlled way so that the Diesel Gen can continue running the Ship whilst the GT's are brought back online.
The problem with the design is that really you want to rip out the GT's and put in the now more reliable available GT sets. But as that would involve effectively cutting the ships in Half it really is a bit of a last resort never done it, don't want to try it procedure.
So as a "fix" put in the bigger Diesel Gen Sets that at least gives you a decent chance at keeping going even if it is at 8 to 12 knots and fighting the ship whilst you engineers run around like blue a***d flies getting your main propolsion system back online.
So the core problem is the GT's as I understand it, not the Diesel side which if brought online in a controlled mannor do fine, but just can't deal with a big dump on them. You may argue that the original design should have had redundency built in, but you pays your money and takes your choice I suppose.

I found a link that confirms your explanation. Apparently the inter cooler used on the WR 21 GT is the root cause of these engines shutting down which causes the overload on the diesel gensets then resulting in a trip-out. Thus the diesel gensets are not really undersized if the GTs performed as intended.

Perhaps the the more mature LM2500 GE GTs (the acceptable alternative) should have been selected as a less risky option. As for the solution, installing larger diesels, this considered more practical than replacing or modifying the GTs. Assuming there were clues about the intercooler problem early on with the WR 21s, one has to wonder why LM2500 GTs were not selected for the QE class carriers.

Putting the Type 45 propulsion problems in perspective | Save the Royal Navy

 

[RobWilliams]

Assuming there were clues about the intercooler problem early on with the WR 21s, one has to wonder why LM2500 GTs were not selected for the QE class carriers.

QEC is powered by a pair of MT30 marine gas turbines, IIRC the most power dense marine gas turbines on the market based on the Trent 800.

 

[John Fedup]

QEC is powered by a pair of MT30 marine gas turbines, IIRC the most power dense marine gas turbines on the market based on the Trent 800.

My mistake. Some quick reading indicates the MT30 is an impressive marine GT. Is its intercooler design different from the WR 21? IIRC, unlike the MT30, the WR 21 was derived from RB 211/earlier Trent aero engine engine designs.

 

[swerve]

I found a link that confirms your explanation. Apparently the inter cooler used on the WR 21 GT is the root cause of these engines shutting down which causes the overload on the diesel gensets then resulting in a trip-out. Thus the diesel gensets are not really undersized if the GTs performed as intended.

Perhaps the the more mature LM2500 GE GTs (the acceptable alternative) should have been selected as a less risky option. As for the solution, installing larger diesels, this considered more practical than replacing or modifying the GTs. Assuming there were clues about the intercooler problem early on with the WR 21s, one has to wonder why LM2500 GTs were not selected for the QE class carriers.

Putting the Type 45 propulsion problems in perspective | Save the Royal Navy

WR21 is British. LM2500 would have had to be imported.

 

[AegisFC]

Now the problem is the ships were built around the GT's with no removal access to them. IE the GT's are effectively "sealed for life" in the ship.

I am having a hard time believing this and if true it is a monumentally stupid decision. In US ships (or US derived ones) GT's are fairly easily swappable with removal usually accomplished through an exhaust stack.

 

[StobieWan]

Now the problem is the ships were built around the GT's with no removal access to them. IE the GT's are effectively "sealed for life" in the ship.

That'd be a dramatic shift in design philosophy from previous RN combatants where the GT's were always intended to be easily replaced as swap out components.

I doubt they're sealed in there but if you can provide a source, I'd be grateful.

 

[StobieWan]

Assuming there were clues about the intercooler problem early on with the WR 21s, one has to wonder why LM2500 GTs were not selected for the QE class carriers.

Probably the same reason the LM2500's weren't chosen for the DDG1000 ..the MT30's are a pretty good GT.

 

[Volkodav]

It is rare these days to design a gt that can't easily be removed and replaced, even the LM2500 in the AMZACs, which was never intended to be removed, i.e. no removal route was provided, can still be broken down for removal and replacements. The WR21 is designed with a recuperator to recover heat and possibly kinetic energy from the exhaust of the core GT, as such the system is very much designed around that particular type of GT. This makes me wonder if some bright spark hasn't suggested replacing the WR21 with some other type of GT (say the MT30) and been told this is not feasible, which has become "the GTs cant be replaced"

I still suspect some of the problem is how they are being operated and how the software driving everything responds to the resulting operational inputs. For instance the RAN managed to break the propulsion system on their ex RN LPD Choules.

 

[The Ginge]

It is rare these days to design a gt that can't easily be removed and replaced, even the LM2500 in the AMZACs, which was never intended to be removed, i.e. no removal route was provided, can still be broken down for removal and replacements. The WR21 is designed with a recuperator to recover heat and possibly kinetic energy from the exhaust of the core GT, as such the system is very much designed around that particular type of GT. This makes me wonder if some bright spark hasn't suggested replacing the WR21 with some other type of GT (say the MT30) and been told this is not feasible, which has become "the GTs cant be replaced"

I still suspect some of the problem is how they are being operated and how the software driving everything responds to the resulting operational inputs. For instance the RAN managed to break the propulsion system on their ex RN LPD Choules.

The point is that yes it can be done, but basically you have to crack the ship in half, remove a good chunk of the superstructures/exhaust system etc. Effectively you are completely rebuilding the Ship, not something anybody wants to try ! The cost of this alone would be substantial. So the cheaper option of giving them bigger Diesel Gens is being done. If for example one of the GT's completely disintergrated then I am sure that a complete Ship overhaul would be done, at the moment it is known intermitant failures so no need to go to the huge expense of opening up the ships.

 

[RobWilliams]

I'd like a source on this one.

 

[swerve]

Me too. What is so special about a Type 45 that the ship needs to be more or less dismantled to remove the GTs? Why can't the WR21s be partly dismantled in situ & removed through a fairly modest hole? As far as I can see, the main engine room can be accessed through the side of the hull.

 

[Volkodav]

Yes I definitely think we need a source on the GT issues as the only information I have been able to find either generally refers to the propulsion system or specifically to the DGs, nothing on the GTs. I did find references to problems with the MT30s in LCS1, root cause of which was salt water spray ingress at high speed causing accelerated deterioration, but nothing bad on the WR21. In fact everything I could find, specifically mentioning theGTs was neutral or positive with no mention of problems, i.e. fuel consumption was lower than anticipated, acceleration was faster.

What I have picked up through the comments sections of many of the stories is the same sort of uninformed ranting I usually associate with Australia's AWD and submarine projects, or the F-35. It seems to me that most of the noise about the Type 45 is uninformed ranting by people determined to find fault and blow it out of proportion than to accept that every project has teething problems that require clear air to get fixed.

 

[John Fedup]

Yes I definitely think we need a source on the GT issues as the only information I have been able to find either generally refers to the propulsion system or specifically to the DGs, nothing on the GTs. I did find references to problems with the MT30s in LCS1, root cause of which was salt water spray ingress at high speed causing accelerated deterioration, but nothing bad on the WR21. In fact everything I could find, specifically mentioning theGTs was neutral or positive with no mention of problems, i.e. fuel consumption was lower than anticipated, acceleration was faster.

What I have picked up through the comments sections of many of the stories is the same sort of uninformed ranting I usually associate with Australia's AWD and submarine projects, or the F-35. It seems to me that most of the noise about the Type 45 is uninformed ranting by people determined to find fault and blow it out of proportion than to accept that every project has teething problems that require clear air to get fixed.

My earlier post on this thread (#11305) has link which contains the following;

"The WR-21 GTs were designed in an international partnership with Rolls Royce and Northrop Grumman Marine Systems. The turbines are of a sound design but have an intercooler-recuperator that recovers heat from the exhaust and recycles it into the engine, making it more fuel-efficient and reducing the ship’s thermal signature. Unfortunately the intercooler unit has a major design flaw and causes the GTs to fail occasionally."

Thus both the GTs and diesels are ok, it is the intercooler-recuperator that is the problem.

 

[Volkodav]

So it is a case of finding and implementing a fix for the design problem and not of replacing the GTs, not on of replacing, or even supplementing the DGs or GTs. None of this seems to explain the plans to fit an extra DG, unless that is to fix an unrelated problem of insufficient power generation on diesels alone.

 

[StobieWan]

The point is that yes it can be done, but basically you have to crack the ship in half, remove a good chunk of the superstructures/exhaust system etc. Effectively you are completely rebuilding the Ship, not something anybody wants to try ! The cost of this alone would be substantial. So the cheaper option of giving them bigger Diesel Gens is being done. If for example one of the GT's completely disintergrated then I am sure that a complete Ship overhaul would be done, at the moment it is known intermitant failures so no need to go to the huge expense of opening up the ships.

You're not getting what we're saying - every other RN ship prior to this and post to this, you can extract the GT's alongside as a plug and play removal- I've seen it done on a type 42 and there's ample evidence to indicate that generally the GT's can be replaced on any RN ship without any of the drama you are alluding to.

 

[John Fedup]

You're not getting what we're saying - every other RN ship prior to this and post to this, you can extract the GT's alongside as a plug and play removal- I've seen it done on a type 42 and there's ample evidence to indicate that generally the GT's can be replaced on any RN ship without any of the drama you are alluding to.

I am not sure if the WR21 GTs are an easy plug and play or if their intercooler recuperation system somehow makes this more difficult. In any event, they are staying in place and the diesel Gensets are going to be upgraded. My earlier link does mention holes need to be cut into the hull to change out the diesels.