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Good read, glad to see the T26 as a platform is going to maintain the RN’s pedigree of ASW warfare. Now all that’s needed is an ASROC weapon so the frigate itself can actually prosecute targets.


Yes, it would be rather awkward if a submarine was detected 15 minutes after an engine had been removed from the single helicopter on board for some form of maintenance or somesuch.


Cheers for the article, I have a couple of questions.
1. One of the pictures shows HMS Westminster with a newer scimitar style propeller. Why are the propellers still fixed and not using variable incidence?
2. The US Navy LCS ships use Rolls Royce waterjets. These allow the trimarans in particular to hit speeds over 40 knots. At slow speeds how do the waterjets compare to a propeller for noise?
3. Due to the probability that T45 will be getting a radar upgrade in the near future and that Dragonfire may be installed as part of the CIWS system, would it not have been a good opportunity to replace the WR21 with the MT30?

Phillip Johnson

Fixed pitch propellers can be made extremely low noise over selected speed ranges but once you get beyond that speed range they can be louder than a variable pitch propeller. It is fair to say that both the T23 and T26 are/will be extremely low noise at sub hunting speeds but a quite identifiable at higher speeds.


The main advantage of controllable pitch propellors is that they provide a quick and easy method of changing from ahead to astern propulsion, they do this by allowing the prime mover to maintain its direction of rotation but reversing the thrust by changing the angle of the propellor blades.

Without CPP there are several methods of achieving astern propulsion, firstly a reversing gearbox can be fitted but this is complex, expensive, heavy and noisy, alternatively the prime mover can be reversed directly. In marine diesels this is achieved by stopping the engine moving the cam shaft (some modern diesels operate without a camshaft and this is performed electronically) and restarting the engine in the opposite direction this takes approx. 30s and as compressed air is used to start the engine can only be performed a limited number of times over a short period of time. In steam turbines and gas turbines this is impossible and a seperate astern turbine must be provided.

In the case of a ship fitted with electric motors (however the power is generated) the motors direction of rotation can be altered electronically and this provides a much neater and simpler method.

CPP has its place but generally isn’t well liked by ship handlers as it provides some “interesting” quirks when maneouvering!

Andy MN

The CPP in my experience creates high amounts of vibration due to cavitation created from any significant pitch change. The hydraulic pitch pumps required to alter the propeller pitch also have a nasty tendency to constantly “sing” adding to any noise signature. Then there is the possibility of leaking hub seals, which will require the vessel to drydock in order to be rectified $$$$. (now amplified by the requirement for all vessels to use sh1te (for the system) environmentally friendly green oils) . Added to this the gearbox oil pumps (both mechanically and electrically driven) can be quite noisy. When any standby hydraulic pump kicks in there is an initial noise burst, due to any trapped air, cold pumps & so on . As the vessel ages it all gets worse. The whole system needs cooled & it takes up plenty of space and incidentally all that space is normally below the water line.
Yes Diesel electric propulsion is the way ahead. Utilising Frequency drive motors, they are very efficient and able to be removed for maintenance quite easily. Down side is any possible harmonic interferences and the fact that they are an asynchronous motor and therefore don’t eat KVAR. Some generators now require low KVAR trips as well as reverse power protection. (MEOs will understand. )
They (frequency drives) have been around now for over 20 years and Rolls Royce are the world leaders.
Actually I was on Leanders and they where surprisingly quiet for the time.


Yep, that pretty much covers it.

Harmonic frequency interference is an issue that can be worked out by very careful design however even then there are quirks. The LPDs had issues with a frequency harmonic in a very very extreme sub harmonic. It screwed up the hotel load provided to weapon systems ( Which require a stable frequency) for some time until a design fix was implemented.


Controllable pitch propellers are designed to give optimised performance over ship total speed range, approx one third more expensive than a standard FPP, the fixed pitch propellers for T26 optimised to give lowest cavitation/noise at low speeds for ASW ops, drawback not so efficient at higher speeds and reduce possible max speed (propellers are the main source of noise but are also very important for vessel efficiency)

My understanding waterjets optimised for high speed, noisy and expensive.

Have seen no hint that T45 will be getting radar upgrade?

Dragonfire is a low power proof of concept laser, would have thought its low power make it of very limited use in an operational AAW mode except perhaps for small and slow UAVs, assume the DS30 carries out that role at a fraction of cost of laser.


CPP’s add complexity. They require pumps (which generate noise) and a very complex hydraulic system to get the oil into the rotating shaft and down to the prop hub to move the blades. T42 and T22 had CPP systems and the hydraulic connections to the shaft where called the “Snake pit” for a very good reason. Fixed Props are quiet and the same engineering designs that go into fixed pitch submarine props are employed on T23 and T26.

The LCS are a “warship” of about half the displacement of a T26. The water jets are not quiet in operation and rather inefficient at slow speeds. The faster you go with a water jet the more efficient it becomes due to the water being forced into it by the ships speed.

WR21 was not the issue on the T45 …it was reliable and works well …the hoofing big recuperater on the exhaust system was the issue. The recouperater along with the control system for the IEP system have all been worked on and reliability has gone up significantly even in hot climates that where previously an issue. The new DG sets for T45 will mean that the vessels can steam/chug around on DG sets and not the GT sets . The old DG sets did not have the power capacity to allow this.

Supportive Bloke

CPP’s also age and wear and over time slop develops in the mechanism. As the system wears the precision of alignment of the blades degrades. Wether the blades are all of exactly the same pitch is pretty critical to quite/efficient running.

There are a bucket load of reasons not to use CPP’s that go into shock resistance (more shock resistance = more battle damage resistance), maintenance (less moving parts = less maintenance), cost (budgets are tight).

And also and importantly with the extended rev ranges available on the motors and improvements in bladed design CPP’s is no longer as useful as it once was – yes it would be more efficiency in a flat out sprint but not so much power is lost that it is worth degrading the optimal quiet mode even slightly.

This ship is designed, by the look of it, with a marginal gains philosophy of not degrading quietness for anything.


Cheers for the answers. It kind of explains why the US Navy is now placing a greater emphasis on a dedicated ASW frigate rather than using their LCS program. One of the key designs of the LCS was modularity, where it would install dedicated modules for specific roles. One of these roles was ASW modules. These looked much like the lightweight CAPTAS towed array housed in an ISO. But as everyone has now said that water jets are inherently noisy and inefficient at slow speeds. This goes a long way to explain the Navy’s need for a dedicated sub-hunter. I realise there’s more to building a sub-hunter than just how quiet its propelled, but if your main means of pushing through the water compromises you, well you’re on to a loser to begin with.

Are variable pitch propellers using hydraulics being replaced with electric servos. Would this not be better for a broader “quieter” speed range and less complex?

There have been reports that the T45’s S1850 will be upgraded from a PESA array to a full AESA array using the latest Thales SMART-L MM/N technology. This radar has been fitted to the Dutch HNLMS De Zeven Provincien frigate. It was used on the last Joint Warrior exercise to specifically track ballistic missiles. The Navy’s S1850 has proven it can detect and track ballistic missiles, the SMART-L MM just does it better. I believe a lot of the techniques used by Thales were developed off the back of the S1850 experience.

I understand the issues with the WR21’s recuperator, but my main emphasis was on potential growth for the ever increasing electrical demand. I gather that the WR21 is based on the core of the RB211, whereas the MT30 is based on the Trent 1000 core. The MT30 core has a greater growth margin (newer and larger design). So I take it at the development stage of the T45, the MT30 hadn’t been built yet? This was the reason for asking if the WR21 could have been replaced with a MT30, especially as they were going to cut holes in the ship’s side for the new diesels.
The RR Trent 1000 series of engines have been having problems with the Intermediate pressure turbine (IPT) blades suffering fatigue cracks at the blade roots. This has been found due to sulphurisation affecting the nickel alloy which comprises the Trent’s IPT blades. Why this only happens at the ITP stage rather than the hot power turbine stage is still being investigated. But it’s funny how the engines are mostly failing over Asian countries, in particular China. Mind you, I suppose a ship with a MT30 won’t be operating at 45,000ft and therefore not flying through sulphur clouds!

CDR Chip

The LCS waterjets are so noisy that the ships cannot be made into effective ASW platforms.


Interesting, good information!
Glad to hear that GE haven’t closed the Rugby plant and moved production of the electric motors to France! A (shamefully rare) move by the government to protect British manufacturing and expertise)


Great article – very illuminating and interesting. It’s good to shine a light on this expertise as it’s arguably one of those fields where UK engineering is leading the world.

I think the USN will be missing out if they can’t let the T26 into their frigate competition down the line.


Thanks for well researched article, a few comments

“a single unit [MT30] can propel the 6,900-tonne warship up to at least 28 knots” though BAE do not state it presume the 6,900 tonnes they quote is the light displacement?, the Australians quote Hunter as 8,000 tonnes FLD and EOL as 8,800 tonnes, 10% allowance built in for normal ship life growth. The only claim seen from BAE is for 26 knots +, will depend on actual displacement at time.

The propeller shafts manufactured in France by DCNS, now renamed Naval Group
The fixed pitch propellers manufactured in Waren, Germany by RR, not sure if still a RR company, RR sold off Rolls-Royce Commercial Marine (RRCM) in April to Kongsberg for ~£350 net to help fund the £1.5 billion hit RR taken to cover losses on their Trent a/c engines due to tech problems.

Nowhere have seen mention of the power of the T26 GE electric motors, the German 7,200 tonnes F125 class use two Siemens EM rated at 4.7 MW each, Italian FREMM class 6,700 tonnes two 2.1 MW EM, mention of ~ 20 knots and 16 knots respectively, which looks about right as the rule of thumb is that for every 4 knot increase in speed requires double the power. Until the power of the GE EM motors revealed will not get a feel of T26 speed in DE mode.


The Australian Hunter version would be ideal as it has been designed to link in with US combat systems. Co-operative engagement capability, Aegis level 10 etc.


Proof if ever it were needed that Great British Engineering is alive and kicking.


Great article.
As the_marquis says hope the USN consider the T26.
With T31 looking like it will be getting the 40mm Bofors will we see the Phalanx in the picture above replaced with the 40mm bofors.


Fingers crossed. An upgrade to the 40mm Bofors with guided ammo for the escorts would be massively beneficial in literally every engagement scenario


Yeah and we have more chance of using it in engagements compared to last ditch Phalanx.


Shouldn’t poo poo the R2D2s, they serve their purpose. T31s in the straights of Hormuz, close qtrs., crappy gun boats, drones etc. yes 40mm, no argument here. T26’s in the cold expanses of the N. Atlantic, Oscars, Akulas, P-800s and Zircons, sorry but it’s Phalanx every time.


My thoughts are that the Phalanx should be kept. Perhaps, if there’s space the 40mm should be looked at to replace the DS30, primarily because of a greater ammo choice, but more importantly it adds to the ship’s anti-missile defence which the DS30 doesn’t. As we use a multi-layered approach to air defence, ranging from SeaCeptor to passive countermeasures. The CIWS debate keeps going, the Phalanx for all its faults is still a self-contained standalone system. This could be crucial if the ship’s only 3D radar decides to fail. The Phalanx has its own radar, IFF and optical sensor, so it can still search, track and prosecute targets.

Then there’s the tungsten rounds, an anti-ship missile flying through a stream of tungsten rounds will get f****d up. The missile out of necessity has it’s seeker in the nose, this could be a bit of fibreglass covering a radar antenna or a clear piece of acrylic for an optical sensor. Therefore, the nose will be unarmoured. The tungsten rounds will shred this sensor and probably keep going through the missile and thereby destroying it. At the worst it will leave the missile blind and thus turning it into an unguided rocket. This is fine for subsonic and probably supersonic missiles as the engagement range is still far enough away from the ship. However, I have my doubts over what will happen against a hypersonic missile. I have no doubt that the tungsten rounds will shred the missile, it’s just at these speeds the debris will still have enough forward kinetic momentum to hit the ship. Whether this debris has sufficient mass to do any damage will need investigating, as it would also be dependent on what area of the ship was hit.

There is a better option than the Bofors 40, and that is the twin 40. The Leonardo Dardo uses a twin 40 L70 set up, it has a dual ammo feed, but more importantly has double the rate of fire at 15 rounds a second. Unfortunately, it is not a stand-alone system and requires target acquisition from the ship’s sensors. Therefore, it would require its own sensors to give the ship better capability redundancy. The turret comes in two flavours one with a self-contained magazine and one with a magazine below the deck if you need a bigger magazine. Crucially though, is that the 40mm round has double the effective range of the 20mm Phalanx. If the gun is armed with the OKRA guided round, there’s an even greater chance that it will either hit the incoming missile or be close enough to damage it, especially for missiles that start jinking when they get close to their target. This may be enough to ensure the debris from a hypersonic missile falls into the sea rather than hitting the ship. I suppose if the debris field has a large enough mass, the Phalanx will engage it and break it up further.


Leonardo Single fast forty has a C model with its own Micro FCS. Carries 72/72 rounds (1 mag of whatever you want and the other with APFSDS for sub 1000m work)


Phalanx problem isnt the Radar or FCS but the M61 Vulcan Gun. The gun is the limiting factor as its very short ranged and it will struggle with high supersonic/hypersonic threats as they will spend so little time within its engagement range. There has been a shift away from the wall of Tungsten APDS bullets (20mm and various 30mm) to larger, longer ranged Proximity Fused Grenade like shells (35mm AHEAD, 40mm 3P and 57mm 3P) Even Raytheon who make Phalanx designed Sea RAM to suppliment and Replace Phalanx. The US Navys next Batch of Arleigh Burkes with have Sea-RAM


If you’re wanting to change out the Bofors and keep it 40 mm, then why not the new CT40 that the army are bringing into service? I’m sure they have a navalised version, it has a lot of fancy rounds and there’ll be a significant cost saving in the maintenance, training and economy of scale areas. It’ll likely be a smaller turret, too.


Apparently the astronomic cost of 40mm ammunition is causing the British Army to re-examine the purchase of the 40mm gun to be mounted on the latest personnel carrying disasters ordered for the poor bloody infantry. At least it will not now be replacing the Rarden on the soon to be scrapped Warriors. So it is par for the course that this 40mm gun will appear on a class of Royal Navy warship in the near future just to disprove that the “fitted for but not with” theory does not now exist but the “cost a packet” theory still does.

Meirion X

5 inch gun Not needed for Type 26, 57mm much more useful for T26.

Gavin Gordon

I’m certainly no expert on the relative merits of one gun type over another (and definitely not in all aspects of their performance envelope which I’d best leave to the RN!), but did carry out a simplistic attempt at estimating the actual ‘useful weight of metal’ over set time span (2 sec) from a number of actual and proposed mounts, arriving at:-
Mk8 4.5″ = 21kg; Bofors 57mm = 19kg; Mk45 5″ = 21kg and for comparison OTO 76mm SR = 25kg.
I’m more than happy for someone with knowledge to shoot me down, though!


“Useful metal” in a 2 second burst doesn’t really convey anything important. Focusing on CIWS, it’s not about how much metal you throw up, it’s “can you down the target before it hits you?”.

Phalanx achieves this with the traditional spray of 20mm cannon fire, the 40mm Bofors does it with a hail of guided shells, and SeaRAM does it with small missiles. The debate on the most effective way to stop them is probably going to keep raging until we have another naval war that proves or disproves it, but based on performance stats, light ballistic gunfire isn’t going to stop anything outside of a few hundred metres, at which point supersonic or hypersonic weapons are still highly likely to hit the ship. Another potential limiting factor for Phalanx in particular, on mount radar systems and FLIR sights are pretty short ranged. To actually prepare the CIWS to engage a Mach 5+ hypersonic target travelling around 2km/s, you need it integrated into the ships main radar anyway. Standalone systems are acceptable for auxiliaries and such, but on a warship they’re just a bit old fashioned.

Missiles are much more reliable in theory, with larger engagement envelopes and higher kill chances. The only downsides really are cost, technical expertise, and being somewhat counter intuitive: on a frigate or destroyer, having already tried and failed to stop an attack with bigger, more capable missiles, to fall back on smaller, less capable missiles. There’s a certain primitive security in the traditional last ditch blast of gunfire, like throwing rocks to keep predators away.

Bigger guided shells have a much higher kill probability at a longer range compared to existing systems like Phalanx or the AK-630, and are both cheaper and more useful in the real world than missile systems, but because they’re still a fairly recent development and we’re in an age of tight defence budgets everywhere but China, they haven’t become as widespread as you’d expect.


Sadly there are a lot of people here who do not realise that there is more to making a ship quiet and the factual situation is that the T26 hasn’t met the required figures asked for by the MOD due to cost. It will be interesting to see being as the ASW type 23s are not as successful at hunting submarines at the MOD will tell you. The T26 us using the same equipment.

Someone show me how the T26 is costing the joke figure of 1 billion to build.


I don’t get why T26 need to be so heavy and big.

Simon m

Great article and good eye opener many thanks


interesting article, I’m so glad the motors Factory in Rugby is staying open, we’ve lost far to many company’s and heavy engineering sites in the past 50 years! Far too many! Never mind all our heavy industry!. We once pushed far far above our weight in these areas and it’s sad to see it going and gone! Ship building and steel and aluminium plants alone employed hundreds of thousands!

Nigel Collins

A very detailed description of how it works.
No doubt we can expect to see a similar layout on a future Chinese version
of the Type 26 Frigate.

Will O

The prop shaft lengths look to be the same, which (presumably) means no cancellation of torsional vibration (compare this design to the asymmetrical shafts on the T45). Isn’t symmetry something a design optimised for quietness should look to avoid, to negate resonance & thus amplification of unwanted noise?
I’m not knowledgeable about such things, I just find it rather puzzling.


I think the reason for offset shafts on T45 (and indeed QE) is survivability.

Being a IEP design the only possible drive is via the motors, thus the two motors must be housed in different, separated, compartments. Flooding of a motor will disable the respective shaft but the other motor, being housed in a separated compartment, can continue to function.

T26 may use either motors or GT direct drive. Thus for survivability, the motors must be well separated from the GT, with the gearbox compartment in between. I presume it’s therefore also assumed that the gearbox will continue to function, even if it’s flooded.

But it’s arguably still a more survivable design because both shafts can continue to function if any two adjacent compartments are flooded, Vs single shaft redundancy on T45/QE.

That’s my guess anyway.


Another excellent article. This site is the best for keeping up with RN developments and learning more information.

US ships use their prairie/masker system to reduce noise from props and engine compartments. Does the T26 have anything similar, and if not, do you know why? The US must value the system, as they fit it to a large number of their vessels across many classes.


Good article and an interesting read.

I can’t help thinking that there was scope for producing a lower cost GP variant of the T26.
Remove the towed array, fit a basic sonar and a less stealthy version of the propulsion system optimised for performance.
Fill those Mk41 cells with land-attack and anti-ship missiles and you would have a pretty decent GP warship capable of operating alone or as part of the carrier task group.

With no requirement for naval gunfire support, they could have removed the 5″ gun from the ASW variant and fittel something smaller forward for self-defence. This would have left space for additional VLS cells for ASROC or more/longer ranged SAMs.

Meirion X

Adversaries would see and hear a GP T26 coming, and be prepared for it, a top target.
Ok for air defence like a T45.
Anyway the Arrowhead T31 has been selected as the GP frigate for the RN, likely armed with NSM.
This issue has been discussed before in past posts!


So you are a discussion Nazi?
I’m not saying “Make a noisy ship” I’m saying don’t spend over the top to make it ASW quiet. I also phrased my reply historically ie “Was scope”
I do hold however that it is stupid to place a 5″ gun intended for NGS on your super stealthy and expensive ASW assets and leave your cheaper GP ships with a light weapon.


I don’t see any redundancy built into it for damage control. The FREMM has generators fore and aft in case either end of the ship gets hit the other half can take over. With the azimuth thrusters they can keep operating even if the shafts are damaged. If T26 takes a torpedo it is out of action.

Keith Wright

Can anyone please, please tell me why the T26 has not gine for combined diesel electric AND gas turbine rather than OR gas turbine???
Surely all the infrastructure is there anyway so can;t be cost (I would have thoght)?
Can’t be weight either for the same reason?

If the two were combined the optrion for circa 35kts would be there with someting in excess of 60k SHP.

Is it possibly to ensure all trhe hotel facilities will always be supplied no matter what the GT is kicking out?

MAny thanks for any answers


Keith Wright

Thinking about my last and on reflection perhaps the GT has enough power to propel the hull (design) to its maximum taking into account the physics of flow and resistance etc.
Therefore any extra power would simply be a waste of fuel????


I don’t know why anyone would down vote you for a factual comment. I calculated that 29 knots is the efficient speed using the displacement boat speed calculator. Anything above this speed requires exponential use of power. So I think you are correct.

carlos Barrera

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