Why don't dieseal subs use pumpjets propulsors

[LoBlo]

Why don't the state of the art diesel electric subs like the Collins or the Type 212 use pumpjet propulsors like the Astute, Trafalgar, or VA?....:hmm: Supposedly pumpjets are more efficient so the subs would gain longer ranges with more fuel effeciency hypothetically. What's keeping them from equipping them?

Ideas?

[aaken]

One thing is that pumpjets have higher inertia than propellers so they do not respond as quickly as an unshrouded propeller to speed variations. I imagine that for shallow water operations this has a certain importance.
Also, not all shrouded propellers and pumpjets are more efficient than propellers, and not in all ranges of speed.
in brief:
a shrouded propeller with an accelerating shroud (i.e. a duct in which the water accelerates from the inlet to the outlet) is generally more efficient than an unshrouded propeller. This is in part due to the fact that the propeller/duct, creating a lower pressure or suction field on the inner side of the duct itself, creates a positive thrust on the shroud. This thrust more or less compensates the additional drag that the above mentioned suction field generates on the after body of the boat. In reality the shroud itself has a certain drag so the thrust that has to be produced by the shrouded propeller may not always be smaller than the thrust that should be produced by an equivalent unshrouded propeller.
But I don't think that submarines use accelerating ducts because a shrouded prop with an accelerating duct has smaller diameter and higher rpm than a shrouded propeller with a decelerating duct and it should be more noisy.
On the other end, a shrouded prop with a decelerating duct creates a negative thrust on the shroud therefore the thrust that has to be produced can be (and usually is) larger than the thrust produced by and equivalent unshrouded prop. On the other end it usually has better efficiencies than shrouded props with accelerating ducts (working with the same outlet-inlet speed difference) because it has higher specific diameters. Also it has the advantage of having lower rpm and lower loads. Having lower rpm it is less prone to cavitate (at given depth and given boat speed) than an unshrouded prop.
But since a diesel sub operates most of the times at low speed the andvantages of a pumpjet are very limited in terms of quieting and could actually increase the Ah consumption.

[Kapitan]

http://i7.photobucket.com/albums/y262/russian-navy01/Alrosa1.jpg

http://i7.photobucket.com/albums/y262/russian-navy01/Alrosa.jpg

http://i7.photobucket.com/albums/y262/russian-navy01/Alrosa2.jpg

[hyperion2206]

Am I wrong or is this a Kilo class?????:huh:

[Kapitan]

Black sea fleet Kilo class submainre her name is alrosa trailing a waterjet propulsor unit and above thats what one is close up, pictures taken in sevstopl.

[hyperion2206]

Cool, I've always loved the Kilo class but now she looks even better! I wonder if the pumpjet makes them even more silent than they are right now.:hmm:

[Kapitan]

According to many sorces alrosa is slightly quieter than the contempary kilo but not by much.

[hyperion2206]

So the alrosa is some kind of experimental sub or will they upgrade the rest of their Kilos?

[LoBlo]

Black sea fleet Kilo class submainre her name is alrosa trailing a waterjet propulsor unit and above thats what one is close up, pictures taken in sevstopl.

Hehe, right on time Kapitan. I was waiting for you to post that pic...:) ... question is though... why is this the only Kilo with a pumpjet? If its that good shouldn't all Kilos from now on use them?

And it still is strange that the other newer SSKs have decided not to bother with them...

One thing is that pumpjets have higher inertia than propellers so they do not respond as quickly as an unshrouded propeller to speed variations. I imagine that for shallow water operations this has a certain importance.
Also, not all shrouded propellers and pumpjets are more efficient than propellers, and not in all ranges of speed.
in brief:
a shrouded propeller with an accelerating shroud (i.e. a duct in which the water accelerates from the inlet to the outlet) is generally more efficient than an unshrouded propeller. This is in part due to the fact that the propeller/duct, creating a lower pressure or suction field on the inner side of the duct itself, creates a positive thrust on the shroud. This thrust more or less compensates the additional drag that the above mentioned suction field generates on the after body of the boat. In reality the shroud itself has a certain drag so the thrust that has to be produced by the shrouded propeller may not always be smaller than the thrust that should be produced by an equivalent unshrouded propeller.
But I don't think that submarines use accelerating ducts because a shrouded prop with an accelerating duct has smaller diameter and higher rpm than a shrouded propeller with a decelerating duct and it should be more noisy.
On the other end, a shrouded prop with a decelerating duct creates a negative thrust on the shroud therefore the thrust that has to be produced can be (and usually is) larger than the thrust produced by and equivalent unshrouded prop. On the other end it usually has better efficiencies than shrouded props with accelerating ducts (working with the same outlet-inlet speed difference) because it has higher specific diameters. Also it has the advantage of having lower rpm and lower loads. Having lower rpm it is less prone to cavitate (at given depth and given boat speed) than an unshrouded prop.
But since a diesel sub operates most of the times at low speed the andvantages of a pumpjet are very limited in terms of quieting and could actually increase the Ah consumption.

I've read different semantics on the categorization of propulsors. Some of what I've read states that a pumpjet isn't necessarily a accelerating or decellerating duct. But one that places a stator in front of the rotor to introduce pre-swirl or after the rotor to eliminate wake swirl in other to increase the prop efficiency.

[hyperion2206]

I think that pumpjets only make sense if you have a SSN. With a pumpjet you can travel fast and still be relative quiet while a propeller would already cavitate at the same speed. Does anybody if my assumptions are correct?

[Kapitan]

Alrosa was designed to be test platform for this propulsion unitthey havnt fitted them to all ther kilos becuase its not realy worth it financialy most will be gone if not all by 2012 replaced by the amur and lada.

what you see on launch day is not the propellor that submarine uses its just there for show and to stop prying eyes having a good look into some sensative areas.

[Kapitan]

Also a diesel or fuel cell AIP submarine is more than quiet enough without this system, the gotlands of sweden have totaly re written ASW for the USN in a year theres roumers that the USN have now scripted the war games to at least give the americans something to do.

[hyperion2206]

I heard that the German Type 212 subs are now one of the most quiets subs around. However I've got a question concerning the Kilo class, Kapitan: Do you know why the Kilos were never fitted with a towed array?

[Zerogreat]

Kapitan: Do you know why the Kilos were never fitted with a towed array?

They weren't? :hmm: I though they were :)

[Kapitan]

Kilos were never fitted with TA becuase they were not intended for blue water ops ie mid atlantic they were designed as a medium range sea going and costal defence submarine a towed array in shallow waters is useless to any sub as it drags on the sea bed.

Kilo is also thought of as an intercept submarine just like the alfa this submarine type alfa didnt have a towed array either becuase she was designed purely for speed (45 knots)

[Kapitan]

Also the german type 212 / 214 are supposed to be the quietest submarines ever constructed yes, true information on these submarines will be classified for atleast 50 or so years so we wont know untill then whats what realy.

[hyperion2206]

Kilos were never fitted with TA becuase they were not intended for blue water ops ie mid atlantic they were designed as a medium range sea going and costal defence submarine a towed array in shallow waters is useless to any sub as it drags on the sea bed.

Kilo is also thought of as an intercept submarine just like the alfa this submarine type alfa didnt have a towed array either becuase she was designed purely for speed (45 knots)

That makes perfectly sense and I thought of it as well but in some missions of DW I could really use a TA!:rotfl:

[hyperion2206]

Also the german type 212 / 214 are supposed to be the quietest submarines ever constructed yes, true information on these submarines will be classified for atleast 50 or so years so we wont know untill then whats what realy.

If memory serves right the US tried to buy a 212 or the shipyard to get information about the construction plans. I don't know if it's true, just a rumor I've heard.

[Kapitan]

You hear many roumers the fact that all ship yards are part share owned by the german government doesnt help !

Kilos have a crush of 340 meters blue water and under ice isnt realy a good place to be costal is a good place for them and thats where they should stay.

[hyperion2206]

I always get a bit confused with the German sub classes but don't they sale 3 212 to Israel?
And concerning the Kilos: I totally agree with you.

[Kapitan]

Well the kilos will be phased out soon, of the 24 built for russian service only around 12 remain the design is over 20 years old and there is just no point anymore updating them or anything like that, hence why the alrosa's propulsion unit never got fitted to other boats.

Germans started sub making after WW2 with the type 205 they then built the 206 207 209 210 212 and 214 each better than the last, they also built the TR1700's whic are type 209-1700 for argentina.

Germans make quality submarines and good tech however for flair and style that firmly goes to the russians.

[hyperion2206]

Too true! Sadly we're just famous for functionality and other stuff related to that.:shifty:

[Kapitan]

Doesnt mean the kilos are now useless, in fact far from it! theres two 55 year old whiskeys running round also a golf which is 60's sub tech going about, ive seen first hand romeo's they were in build in the 50's seen foxtrots also.

kilo will be good to countries like india for atleast another 20 maybe 25 years they are a good unit solid well built, its just the super power cycle thats all.

if your a super power then longest you will have any sub before its deemed obsolete is around 25 years even if a submarine is bsolete when it hits the water it still has some use.

The americans launched the 688i's they were obsolete come 1990's as the russian akulas surpassed them, hence why they went on to go and re start project seawolf, then after that the follow on project virginia. and i bet theres plans being drawn up for thier replacement.

[aaken]

I've read different semantics on the categorization of propulsors. Some of what I've read states that a pumpjet isn't necessarily a accelerating or decellerating duct. But one that places a stator in front of the rotor to introduce pre-swirl or after the rotor to eliminate wake swirl in other to increase the prop efficiency.
The presence of a stator does eliminate the swirl of the rotor but the pump itself (stator or NGV and rotor) is inside a shroud. It's importance is capital because it defines if the flow itself accelerates or decelerates and in which parts (for a pumpjet with a rotor and a stator, at the exit of the stator the flow has lost the tangential speed or swirl imparted to it by the rotor and therefore its pressure is increased. this pressure will be trasformed in speed by the nozzle so in the nozzle you'll almost always have acceleration of the flow, but what happens to the flow from the inlet up to the stator of the pump, and indeed the parameters based on which you'll design your pumpjet, depends substantially on the form of the shroud). Also, the shroud, depending in which way you design it, for the suction field I've written before, determines part of the drag of the submarine and, therefore, the power requirement of the propulsion plant. It is slightly more than just semantics or categorization.;)

[LoBlo]

The America built Benjamin Franklin class was built in the 1960s and they were still being driven around until 2002.

[Kapitan]

Russian built romeos made 1959 still in active service today, russian built golf of 1960's still in active service today russian built whiskeys built early 1950's still in use today.

[PeriscopeDepth]

I always get a bit confused with the German sub classes but don't they sale 3 212 to Israel?

No, actually they got guilt tripped into GIVING them to Israel for nothing. Seriously. All the Israelis paid for was half of the third unit. Quite a scandal in Germany, as the 650mm tubes made it clear what they're there for. I think they're financing 20% of the next two units also.

PD

[LoBlo]

On a side note:

That pumpjet used on that Kilo sure is different looking. I mean it obviously has the rotor showing and the aft placed stator disconnected and on the ground below. But the prop housing itself is strange in that is blends into the aft dive plane and rudder supports. Not only that, but it inlet opening are tightly hugged to the hull instead of the more distant and widely opened pumpjets on the SW or VA.

http://www.combatindex.com/hardware/detail/sea/pic2/ssn21_13.html
http://www.combatindex.com/hardware/images/sea/ssn/ssn21_13.jpg
http://www.combatindex.com/hardware/detail/sea/pic2/ssn774_07.html
http://www.combatindex.com/hardware/images/sea/ssn/ssn774_07.jpg

[hyperion2206]

I always get a bit confused with the German sub classes but don't they sale 3 212 to Israel?

No, actually they got guilt tripped into GIVING them to Israel for nothing. Seriously. All the Israelis paid for was half of the third unit. Quite a scandal in Germany, as the 650mm tubes made it clear what they're there for. I think they're financing 20% of the next two units also.

PD

The last thing I heard of was that Germany will finance about 1/3 of the next 3 units.

[Kapitan]

The pictures of the virginia are of the shrouded propulsor system and not water jet propulsor, hence why they are radicaly diffrent.

[LoBlo]

Whether its a simple shrouded propulsor or a pumpjet depends on the presence or absence of stator blades pre or post rotor iirc. Everything I've read says that the VA is using a pumpjet.

[Kapitan]

Well for an experianced researcher i will tell you this:

DO NOT BELIEVE EVERYTHING YOU READ ABOUT A NEW PLATFORM !

It took NATO a good 10 years to work out the tonnage of the typhoon alone, no navy in its right mind will give you the full specs of a new submarine or one in active duty, theres alot i do know about the russian submarines i cant post it here just like the people who work on the USN RN or any other navy cant.

http://i7.photobucket.com/albums/y262/russian-navy01/tk20.jpg
This is a shrouded propellor (Typhoon class SSBN TK20 Severstal) this is what the virginia has but what she has is way more advanced, infact about 2 generations ahead.

Alrosa is one of a kind kilo SSK, but i can tell you the pictures of this lada class (st petersburg)
http://i7.photobucket.com/albums/y262/russian-navy01/lada027ds.jpg
No matter how hard i try i can only come to say this submarine will not go to sea with this propellor period just look at it seriously why would the russians go 2 steps forward and then take 5 back?

http://i7.photobucket.com/albums/y262/russian-navy01/sskCONN.jpg
This is the old style con (centeral command post (CCP)) normaly found in compartment 4 unless your a phoon its compartment 14, this is what a kilo looks like inside since this the russians are using waterfall displays in all new builds and when subs come in for refit and overhaul they will be changed if its financialy worth it.

Again why take 2 steps forwars 5 back

[LoBlo]

The difference between a shrouded propellar like shown on the Typhoon and a pumpjet is that on that typhoon their are no stator blades providing preswirl to the inlet flow or postswirl cancellation to the outlet flow that would increase propulsive efficiency. To tell if a pumpjet is present on the VA or SW one would need to look at the inlet or outlet in order to discern the presence/abscene of stator blades.

[Kapitan]

do not forget the oldest typhoon is now what 28 years old and this type of propulsion system wasnt around back then, the reason for the shroud on the typhoon is realy only to protect the propellor.

[XabbaRus]

Kapitan the Virginia dose have apumpjet like the Seawolf adn like the S-Boats T-boats. Who do you think designed the pump jet for the seawolf.

I can't say where I got the info but I have a detailed set of pictures showing the stern arrangement of the Seawolf and on good merit was told the Virginia has a very similar system, just the number of stator blades is less.

Pumpjets also don't have scythe shaped blades but rather constant chord profiled blades.

[Kapitan]

Who do i think designed them, no doubt us brits who then sold it on to the americans, and as for the SSN-21's having same similar propulsion system that would make sence.

[Linton]

Trial boat in the Rn was a C-boat back in the 1970s.http://imagen.britishpathe.com/scripts/ImgRetrieve.dll?GetPic&recno=57645&picno=00000010&sif=1
Possible early installation??

[LoBlo]

I've always envisioned the SW outlet to look something like this...

http://en.wikipedia.org/wiki/Image:Propulsor_MK50.jpg

but scaled up to the SW diameters.

[Linton]

Can you back a submarine using a pump-jet or do you need some other propulsion device?

[LoBlo]

From what I understand you can go backwards, but the total amount of reverse thrust is much less than a normal prop. Something abou the stators that while increasing efficiency forward, decrease efficiency in reverse iirc

[Linton]

I didn't think that a pump-jet would be very efficient at going in reverse.I imagine it would probably cavitate more as well due to the flow being reversed through the stators.