April 29, 2016

Shortfin's Pumpjet Propulsor - A Sales Feature?

Note that a Scorpene (2,000 tonne "small" conventional submarine (SSK)) is depicted with a pumpjet. Was the Scorpene pumpjet only an idea in 2005 that was phased out/cancelled? Or is pumpjet a possible future inclusion for Scorpene? Pumpjets have been on French submarines since the first Triomphant class SSBN was launced in 1994. (Artwork courtesy DCNS Australia)
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Here the Scorpene has no Pump Jet, on the Shipbucket graphics website (circa 2010).
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Shortfin concept displaying its proposed pumpjet. Also note its X-plane rudders. (Artwork courtesy Navy Recognition)
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DCNS' 2016 "pitch" for the Shortfin stated: "Pumpjet propulsion means the Shortfin Barracuda can move more quietly than submarines with obsolete propeller technology. In a confrontation between two otherwise identical submarines, the one with pumpjet propulsion always has the tactical advantage.

Will a pumpjet (which appeared then disappeared from DCNS' Scorpene SSK) disappear from the Shortfin SSK? Will the Shortfin then have the bare propeller which practically all SSKs have?  

The submarine speed threshold (14 knots? 20 knots? somewhere in between?) of when a pumpjet becomes tacticly advantageous depends on the situation and needs to be weighed against the downsides of pumpjets.

High pumpjet weight compared to a bare propeller is a common downside. But wouldn't pumpjet weight be scalable? That is would a pumpjet for an average 1,800 tonne SSK be proportionatly smaller and lighter than a pumpjet for a 5,000 tonne Shortfin?

If the scalability argument is valid - what is the main thing distinguishing SSKs from SSNs? Engine power and resulatant speed.

An SSN can operate at 20+ knots for weeks-months while a SSK fully submerged on battery (and even AIP) can only operate at 20+ knots for (probably) 2 days or less. 

(POSSIBLE) ADVANTAGES AND DISADVANTAGES OF PUMPJETS OVER BARE PROPELLERS

Advantages:

-  In the rare but crucial tactical situation where high speed is required to fight another submarine or flee from a surface ASW threat, a pumpjet can allow a higher speed before the onset of cavitation. This means lower acoustic signatures.

-  the shroud of a pumpjet can protect the rotating element (the impeller) from striking hard objects (like rocks or the seafloor). This can assist littoral, shallow water operation.

-  If the pumpjet is steerable it may make the submarine more maneuverable at slow speeds. 

Disadvantages compared to Bare Propeller

-  Can be less efficient than a propeller at low speed, leading to higher consumption of limited fuel (not a concern for unlimited nuclear reactor). This may well include an SSK's typical efficient submerged speed (5 knots?) on battery or AIP.

-  Inability to efficiently reverse or reverse at all to slow down or reverse the submarine? Therefore the sub needs a bow thruster? Or would there be a bow thruster anyway for a Shortfin?

-  heavier, more expensive, complex?

-  Punp jet intake grill can become clogged with debris; e.g., seaweed. (Can be mitigated by being able to reverse?)




The Kilo submarine B-871 ("Alrosa") (launched in 1989 (with pumpjet? or retrofitted?) has a large pumpjet with 7 stators and 11 propulsors. It spends more time in dry dock for repairs and upgrades to its pumpjet than at sea.  The pumpjet appears to be of excessive size - perhaps implying Alrosa is a test vehicle for a pumpjet intended for much larger SSN's or SSBNs. 

COMMENT

It is unclear why pumpjets have not been used for SSKs - leading to more questions than answers, at this stage:

-  are the usual 2,000 tonnes or less size SSKs too small?
-  do the relative lower power of SSK diesels limit their ability to reach pumpjet effective speeds?
-  only used once(?) for a larger 2,350 tons (surfaced) SSK (that being Kilo B-871 Alrosa)
-  artwork of a pumpjet included on a DCNS Scorpene (2,000 tonne SSK) but no evidence (?) it has been adopted for Scorpene.
-  are pumpjets are a recent, expensive, high end, technology only used in already expensive nuclear submarines?
-  pumpjets have not been retrofitted on DCNS' small (2,400 tonne surfaced) Amethyste-Rubis class SSNs, so does that prove small size eliminates pump jets or cost of retrofitting on Amethyste-Rubis would be too high?

It is very difficult to nail down whether the pumpjet proposal for the Shortfin is of sales value but a technology that may be of marginal practical value.

There is the argument that the Barracuda SSN can serve as a prototype to iron out any technical problems before the Shortfins are built? But then, will the speed envelope of the Shortfin be similar enough to the Barracuda for Barracuda to be a pumpjet prototype for Shortfin? Ultimately much will rely on how many knots Shortfin can reliably move - something that may only be apparent in about 2031.

Artwork courtesy DCNS.
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Sources included:

-  https://en.wikipedia.org/wiki/Pump jet and https://en.wikipedia.org/wiki/Propulsor


Pete

28 comments:

MHalblaub said...

Dear Pete,

I think you are a little bit to optimistic about the endurance of an SSK at top speeds. Normal range for Collins-class is given at about 8 or 10 kn. I would estimate the time of an SSK for a proper pump jet speed to be around 4 to 12 hours.

In case RAN is looking for range RAN should opt for the propulsion system optimized for cruise speed. That should be around 8 to 10 kn and therefore a 7 blade standard propeller is better.

To hunt a battle ship, aircraft carrier or something like that RAN would need SSNs. SSK wait and strike.

Regards,
MHalblaub

MHalblaub said...

Some simple math for the weekend.
A submarine with 4,000 t displacement has about twice as much surface as a submarine with just 1,000 t. So the detection range of an active sonar is doubled for a bigger submarine.

Buoys are fixed receivers. You need 4 times as much buoys to get the same chance detecting the smaller sub.

Regards,
MHalblaub

Dave W said...

Hi Pete,

Seems I need to throw my two bobs worth in again.

First the diesel now the pumpjet......

The USN Virginia class submarines utilize pumpjet propulsion and roam the oceans all over the globe including the SCS. Can you cite or otherwise reference a submarine pumpjet fouling due to the examples mentioned? Chances are if it has occurred it is so infrequent as to be no more of an issue than the fouling of propellers by discarded fishing nets.

Retrofitting a pumpjet into an existing submarine, which was designed and built with a centerline shaft would, I imagine, not be economically feasible for an entire class. The Russians did it for one boat.

I share your enthusiasm for a nuclear powered submarine fleet however I do not forsee this ever occurring before Australia embraces a nuclear energy industry (also something I endorse).

I think we owe the CEP some credit, much has been learned from the disasters of the Collins program. I don't agree with altering the design by dropping the nuclear plant and suspect there will be issues but until we start hearing (if we do) specs on the battery capacity and or fitment of AIP and a host of other potentials then I feel it too premature to cast disparities on the choice.

Cheers D





Anonymous said...

Pete,

The Alrosa's pump jet is a retrofit so it lacks the benefits of a clean sheet design.

Pump jets cannot be reversed and that goes for all pump jets.

The higher speed threshold for cavitation noise is only beneficial to the extent the submarine's self noise as well is less than cavitation noise and the ambient noise is greater at that location and the passive sonar suite can still detect targets up to that speed.

According to global security org, the sonar sensor suite on the Rubis class is probably used by the Chinese on their SSN and latest SSK. I hope not otherwise the Chinese will know to some extent the characteristics of the sensors on the Shortfin, since I am sure the Barracuda suite is an improved version upon but still largely based on the Rubis design and their predecessors.
KQN

Anonymous said...

Actually the French first tested a pump jet on an Agosta SSK in the 90s, though that was just a test bed, never meant to be operational.

The Rubis SSNs also have some kind of pump jet. Industry sources say that "it is not quite a pump jet". What that means exactly, no one knows. They're very coy about the subject... However, what is known is that there've experimented with lots of options including shrouded and non-shrowded pumpjets, stators, contra-rotating propellers etc...

I doubt that this is just a marketing ploy. They certainly know the pros and cons by now.

-HK

Peter Coates said...

Hi Guys

I'm intensively on another matter so can't respond to (or process) comments for a short bit.

Regards

Pete

imacca said...

[ Pump jets cannot be reversed and that goes for all pump jets. ]

Thrust reversers as on a commercial jet engine??

Added weight an complexity leading to possible reliability issues?

I'd sat that if it hasn't been done, then its been worked out that in the trade off between maneuverability and signatures, reverse thrust is lower priority.

And on speed. You optimize a prop for a certain speed range and usage profile. Can do same same for a pump jet??

Nicky K.D Chaleunphone said...

Hi Pete,
I know the Virginia class SSN's have pumpjets as well.

Ztev Konrad said...

The French could well have made a technology breakthrough on their shroud/pumpjet ? But Im not expecting all the details to be laid bare. maybe its the materials they build the housing out of that is lighter- stronger - one does come to mind.

Ztev Konrad said...

Interesting little point
Is it the Barracuda or a different fish the Barracouta. Some pictures seems to be the mackerel version, the barracouda

Anonymous said...

Hi Pete

Every contender submitted various simulation data and CEP assessed performance of submarine from view point of expert. In design, result of simulation should be validated and reviewed by actual or proven result from a broad point of view. That’s why proven design or performance has critical meaning. Initially, this proven design or performance was emphasized, but, was not commented at announcement of the CEP decision at all, though the CEP decision reportedly was based on the technology. I do not complain the decision by Australia at all. But, to tell the truth, there are something remained which I cannot understand.

By the way, JMSDF who seriously worried about technology leakage to China was relieved.

Regards
S

imacca said...

Pete mate!!

You may want to also pay a bit of attention to the TKMS bid. :)

http://www.smh.com.au/business/federal-budget/federal-budget-2016-subs-sink-scott-morrisons-credibility-20160502-gojtud.html

"Under pressure from Laurie Oakes with an allegation that the French subs are nearly twice as expensive as the German offering, Morrison said: "This bid we have entered into a negotiation on, so it's a negotiation now, the designs have not even been drawn up yet on what the submarines might be." "

Apparently the French PM is making a flying visit to Australia post the CEP announcement, i guess to try and politically lock things in. No doubt there will be further reporting in France in this?

Its starting to look to me like really, the rushed CEP announcement before the election is pure, local short term politics re: SA.

It may be that actually, on a practical level, we are down to a "short list" of DCNS and TKMS. That's IF the French bid actually WAS so much higher than the German one and its very unclear to me if thats the case. I thought the big justification for 12 boats (rather than 6-8) being the live option was that the bids from ALL the potential suppliers in the CEP stage looked like being considerably less than the initial estimates from Defence?

This has a ways to run. Particularly if there is a change in Govt this year.

MHalblaub said...

A Shortfin with Pump Jet is an advantage for DCNS. They do not have to develop a normal propeller just for Australia.

Just like Japan: claim your shortcomings are an advantage.

Regards,
MHalblaub

MHalblaub said...

I can see no specific reaso why a pump jet like the once used on submarines should not work in both directions. Reversed may less efficient but who cares.

The bow thruster are needed due to the streams around the rudders. Propeller make a wider stream area with more angular force for the rudders. They quite efficient at very slow speeds.

I thought France did make a low ball offer to get some money to keep the Suffren-class development going.

Josh said...

The consensus though seems to be that a pump jet offers lower efficiency but with reduced noise and cavitation at mid level speeds. Given the long transit of Oz boats to their patrol area this might be considered a major advantage, if the fuel and rate of recharge can keep the indiscretion rate sufficiently small and range sufficiently long. Weather the boat can actually listen to its surrounds moving on station may or may not be relevant; clearly US boats cruise at speeds well above the wash out speeds even for the fat line TB-16 arrays. Simply running on charts and assuming you aren't making *that* much noise can justify running blind in a low threat environment.

Cheers,
Josh

MHalblaub said...

A jet engine needs an ongoing stream of air to work properly. So the air is reversed behind the engine. A turboprop engine can reverse thrust be changing the propeller pitch without changing the rotation direction.

The pump jet on submarines work without combustion chambers and so I can see no reason for a reversed mode.


Anonymous said...

When you look at pump jet, the exhaust area is substantially smaller than the inlet area to accelerate the flow and therefore gain thrust. You can see this in the Shortfin mockup. Reversing will be very problematic since there is little thrust in the reverse direction. When reversing the fluid volume is constrained by the smaller area of the inlet (previously the exhaust) plus the flow is decelerating, not accelerating, through the pump jet since the exhaust now has a much larger area.

The sizing of a pump jet is optimized around a submarine's tactical speed. Given the endurance and available power of an SSN is likely not the same as an SSK, the pump jet sizing could be less than optimum if the SSN and SSK both share the same design but only the designers will know that. Marketing powerpoint viewgraphs, anything is top.
KQN

imacca said...

Pete, now that there is a timescale around the Future Subs project, its got me thinking about what will be involved in Collins class sustainment and upgrades in the interim?

Particularly in respect to:

Is it likely that an upgrade to Collins would include new batteries...like LIB's?? AIP is probably too big a change, but LIB's, new power distribution systems, and maybe a Permasyn main motor??

Hmmm.... and those diesels while you have the boat cut open??

Peter Coates said...

Hi imacca [4/5/16 11:32 AM]

Major details of Collins midlife upgrade are at:


http://www.defence.gov.au/whitepaper/Docs/2016-Defence-Integrated-Investment-Program.pdf Page 89 to 90, Table 6, Summary of key investment decisions from FY 2016-17 to FY 2015-26 .

Program title Program Timeframe Approx investment value

Collins Submarine Sonar Replacement Scheduled for approval† $100m–$200m
Collins – Satellite Communications 2019–2024 $750m–$1bn
Collins Submarine – Sonar Replacement 2017–2027 $500m–$750m

The upgrade is likely to include diesel engine overhaul, checking for any hull cracking, derusting outside and inside including in the fuel/ballast tanks (tanks were OK for low salt Baltic conditions, but not higher salt Indo-Pacific waters), new lead-acid batteries. So no AIP, Permasyn, whole diesel replacement or LIBs envisaged (to my knowledge).

Regards

Pete

Peter Coates said...

Hi S [2/5/16 10:16 AM]

Re: "By the way, JMSDF who seriously worried about technology leakage to China was relieved."

Chinese intelligence gathering (especially Chinese sigint (cyber hacking)) is a threat to Japanese weapons secrets on weapons that never leave Japan.

Like established arms exporters Japan will need to get used to a level of expected risk of weapons secrets leakage.

Just like the US isn't exporting its F-22 or B-2 secrets Japan should also have weapon categories Japan decides not to export.

Regards

Pete

Peter Coates said...

Hi imacca [at 2/5/16 1:05 PM]

Probably going too far to say that TKMS still has a "short list" chance.

But Turnbull certainly announced DCNS early as a pre-July 2 election sweetener.

On such a big contract there are many signing stages before everything is approved.

One also needs to include a different CEP for 30% of the project, which is LockMart and/or Raytheon being chosen to integrate the many combat system items.

So years of standard agreement stages await.

Regards

Pete

Peter Coates said...

Hi MHalblaub

A further possibility is that for the Shortfin's slower hull speed DCNS will use a specially modified pump jet - with differences to the Barracuda SSN's pump jet.

Regards

Pete

ONeil Padilla said...

Hi Pete,
Seriously why Can't Malcolm Turnbull & Jay Weatherill Just get together with the French and say Australia will build the hulls and the French the reactors!

No need for the 3 year design phase because we would already have a design in production, less risk, more capability and possibly cheaper.

Oh yes and no CO2 into the atmosphere (got to keep the greenies happy)

Pete any chance of doing an article on the Pros & Cons if Australia were to change to the Barracuda Class SNN?

PS - OK perhaps we would have to include a couple of VLS to get the weapons load to where is should be.

Peter Coates said...

Hi ONeil Padilla

Problems with a quick and easy Australian decision to buy Barracuda SSNs include:

- much higher cost
- France may not want to export its reactor technology as it didn't for Brazil's SN-BR SSN project
- US, Chinese and Japanese opposition
- concern about Aus SSNs encouraging SSN arms race in the region (starting with South Korea then Japan having to build SSNs)
- major problem with Barracuda's K15 reactor is it needs to be refueled (very difficult - across the world in France) about every 10 years
- while US Virginia SSN needs no refueling over about 32 years. Would have made more sense to buy Virginias

Regards

Pete

ONeil Padilla said...

Hi Pete,

I agree with all your points but we have a realistic chance of crewing the French subs than the Virginia's.

I think we're a different proposition to Brazil, the French see the Brazilians as a future competitor in the manufacture of such things hence were reluctant to give them a leg up in an industrial sense. (Australia is not in that category)

Maybe 6 Virginia's are the most realistic bet.

Maybe if the South Australian Royal Commission into the nuclear cycle gives it a big thumbs up then maybe the first couple of subs can be refuelled in France and the rest in SA??

I'm dreaming again aren't I?

Ztev Konrad said...

It would be impossible for Australia to run SSN's. They have struggled with the technical people to run 6 diesel subs. The nuclear knowledge just isnt available in Australia to fully understand the nuclear propulsion system and operations. If it was from France it would put Australia in Frances pocket for the next 40 years, and even a US reactor would mean something similar.
We can remember the concessions that UK made to get the Polaris system back in the early 60s. Which largely consisted of the carving off of the Chagos Archipelago from its territory with about to be independent Mauritius, expulsion of the residents, and turning to island of Diego Garcia into an US colony.
Australia did something similar with Christams/ Cocos Islands, in return for nuclear test operations in Australia, they got these territories from UK in return. ( They were important as cable stations back then) Recently it has become politically convenient to proclaim these remote places as 'not part of Australia'

Peter Coates said...

Hi ONeil Padilla [at 6/5/16 9:59 AM]

A good point about France not exporting reactor in SN-BR technology to Brazil because Brazil could build and re-export them in competition with France.

I don't think the South Australian Royal Commission into the nuclear cycle will produce much. I doubt even a low level nuclear waste (with failed proposals for decades) dump will be built.

I see a disconnect between the limited prospects of the Royal Commission and the higly specialised (economies of scale) process of submarine reactor refueling.

Perhaps Australia in the 2030s might choose between 4 more able (longer mission) Virginias, instead of 6 smaller Barracudas?

Peter Coates said...

Hi Ztev (6/5/16 11:02 AM)

I think Australia is sufficiently close to the US to have US reactor experts watch over Virginia reactors for Virginias Australia may buy. A training regime of Australia reactor exports can happen simultaneously. On submarine closeness I understand that there have been long term secondments of Combat System operators on missions.

What with Australia dependent on Boeing and Lockheed Martin aircraft, desperately courting more Marines for Darwin, more frequent US bombers at RAAF Base Tindal, Pine Gap and not to mention Australia helping out with SeaWeb - Australia buying Virginia's may be just another step.