June 24, 2016

Making the pump jet lighter - likely key aspect for use on Shortfin

The pump jet on a DCNS Triomphant class SSBN. Note the H-plane tail which aids stability when the sub is firing its ballistic missiles . A similar but smaller version of the DCNS pump jet may be going on the Barracuda SSN and eventually the Shortfin SSK.
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Since writing Shorfin’s Pump Jet Propulsor - A Sales Feature of April 29, 2016, I’ve been puzzling  about what is technically new to make a pump jet viable on an SSK viable.

A central problem is that there is a correlation between pump jets and large nuclear submarines. Only companies (or countries) that developed pump jets for nuclear subs were in a position to then develop them for SSKs.

Until recently the weight of steel or other metal alloys may have made a pump jet too heavy for a Barracuda (at the smaller end of the SSN scale) or the Shortfin large SSK derivative. Still further lightening may be necessary before a pump jet is viable for Shortfin.

From looking at the sources in the BACKGROUND (below) it seems that using Nickel Aluminium Bronze alloy and/or epoxy fibre composite for a pump jet's rotor shaft, rotors, stators and the duct/shroud has many advantages including

-  providing a better power to weight ratio for the sub
-  not unbalancing the sub
-  a fully composite duct gives off a minimum magnetic signature
-  composite duct also reduces acoustic signature [See "Submarines - Rolls-Royce" website and within it scroll down to the "Propulsors" subheading] 
-  pump jets are low maintenance
-  all in all, the above help make a pump jet viable for a small SSN or large SSK.

A rotor (brown) and stator (dull silver) can be seen in this Mark 50 torpedo pump jet.

BACKGROUND


[Page 27] Although recent designs of composite propeller systems is classified, the use of modern composites manufacturing allows for continuous fibres to be aligned  with major hydrodynamic and centripetal forces. …The use of composites is now is now being introduced for propeller shafts on large ships (frigates and destroyers) where they account for 2% (100-200 tons) of total ship weight.

Carbon fibre/epoxy and glass fibre epoxy composite shaft shave the potential to be 25-80% lighter than steel shafts…while also providing noise suppression…thus reducing…acoustic signature. Also the non-magnetic properties of composites reduce that signature.”

This 2008 paper for the UK Royal Institution of Naval Architects on page 1 explains meaning of composite:

“A composite material is a material that consists of two components: the fibres and the matrix…The fibres are the part of the composite material that contributes to the strength whilst the matrix holds the fibres together.”

See "Submarines - Rolls-Royce" website and within it scroll down to the "Propulsors" subheading on the benefits of the pump jet propulsor for the Astute SSNs.

As can be seen above several nuclear subs lack pump jets because they lacked (or lack) pump jet technology. It seems pump jets cannot be retrofitted. (SSBN diagram courtesy pinterest)
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Pete

13 comments:

SPI said...

No Typhoons are in strategic service. one is being kept for trials until 2020 and rest going to scrap.

Nicky K.D Chaleunphone said...

Hi Pete,
You may want to sit down and read this because this is an eye opener

Chinese navy offers glimpse of secretive nuclear-attack submarine
http://www.washingtontimes.com/news/2016/jun/23/chinas-nuclear-attack-submarine-revealed-communist/

FIRST PICTURE OF CHINA'S SECRETIVE NEW SUBMARINE
http://www.popsci.com/first-picture-chinas-secretive-new-submarine-type-093b?src=SOC&dom=tw

Peter Coates said...

It seems that the Type 093 photo has been made a cause célèbre among some online forums.

A more professional assessment comes from IHS Jane's http://www.janes.com/article/61727/image-shows-new-variant-of-china-s-type-093-attack-submarine

"...the picture shows that the new Shang-class submarine appears to have a new 'bump' shape after the sail that may be intended to help dissipate root vortices that emerge from the base of the sail, which can help reduce drag and noise...The new photograph, however, does not provide confirmation that the 'bump' also houses vertical-launch cruise missiles."

Nicky K.D Chaleunphone said...

Hi pete,
It seems like it and I think the Type 093B is a newer, VLS version of the Original. What's your take on the Chinese Type-093B

Peter Coates said...

Well Nicky

I think that this so-called 093 "news" is basically a Taiwan propaganda arm beatup - and a distraction from

"Making the pump jet lighter - likely key aspect for use on Shortfin" above.

No more 093 today thanks.

Pete

Peter Coates said...

Hi SPI

Yes. I know that the remaining Typhoon* has served out its time as a massively expensive test stand for the occasionally reliable Bulava missile .

The Typhoons (packed with Titanium) served the West well in bankrupting Soviet Union.

* see https://en.wikipedia.org/wiki/Russian_submarine_Dmitri_Donskoi_(TK-208)#1990-present

Regards

Pete

Anonymous said...

Hi Pete

As a propeller is exposed to severe cavitation environment, cavitation erosion damage [1] is unavoidable. Therefore study on cavitation erosion is quite important for development of propeller materials. Recent study [2] revealed that cavitation erosion resistance of composite materials was inferior to that of NAB (Nickel-Aluminum-Bronze), typical propeller materials.

The strength of matrix resin of composite is lower than that of NAB. Resin fractures rather easily under the cavitation condition followed by delamination of fiber, causing cavitation erosion damage of composite, I think.

It is expected that life time of propeller made by composite is shorter than that of metallic propeller. Trade-off between shorter life time and excellent properties (high corrosion resistance, light weight, non-magnetism) should be considered for adoption of composite propeller.

[1]https://www.corrosionpedia.com/definition/244/cavitation-erosion
Definition - What does Cavitation Erosion mean?
Cavitation erosion is the process of surface deterioration and surface material loss due to the generation of vapor or gas pockets inside the flow of liquid. These pockets are formed due to low pressure well below the saturation vapor pressure of the liquid and erosion caused by the bombardment of vapor bubbles on the surface.
[2]Report of “FY 2011 Research and development of high efficient and low cost propeller by using composite materials” by Japan Marine Manufacturers Association, 2012, page 13.

Regards
S

Peter Coates said...

Hi S

As usual your comments are original, well researched and relevant to the article topic.

Yes the positioning of the pump jet shroud/duct allows faster propeller rotation without the buildup of the chemi-physical conditions leading to cavitation.

I intentionally left it open whether the material promoting light weight would be Nickel-Aluminum-Bronze or composite fibres.

Nickel-Aluminum-Bronze alloy seems to be the material of choice for bare propellers so likely to be used for shrouded propellers.

Perhaps the stators are more likely to be also made of Nickel-Aluminum-Bronze alloy rather than composites?

For the shroud/duct Rolls-Royce submarine propulsion division has chosen composite for the UK's latest SSN (Asute class). [see "Submarines - Rolls-Royce" website http://www.rolls-royce.com/products-and-services/marine/market-sectors/submarines.aspx and within it scroll down to the "Propulsors" subheading] This makes it likely DCNS has chosen composite for the shroud/duct.

As pump jets become lighter experience with them on SSKs is likely to grow. DCNS' objective (in the 2000s) of placing them on newbuild Scorpene submarines may, at last, happen.

Regards

Pete

Peter Coates said...

Hi S

Perhaps composites may not be used used for high stress, fast rotation, naval propellers but some Japanese research suggests composite material propellers may have some advantages for lower rotation speed civilian uses.

see this NAKASHIMA PROPELLER CO., LTD. Press Release
https://www.classnk.or.jp/hp/en/hp_news.aspx?id=1043&type=press_release&layout=1

"Title:ClassNK and Nakashima Propeller Announce World’s First Installation of a CFRP Propeller on a Merchant Vessel"

"Tokyo – Leading classification society ClassNK (Chairman and President: Noboru Ueda) and Nakashima Propeller Co., Ltd have announced the world’s first installation of a carbon fiber reinforced plastic (CFRP) propeller on the main propulsion system of a merchant vessel. The CFRP propeller was installed on the Taiko Maru, a domestic 499 GT chemical tanker owned by Sowa Kaiun YK by Marugame-based Koa industry Co., Ltd. in May 2014....

...Despite its ultra-lightweight composition, CFRP exhibits the same, if not superior strength, to the aluminum-bronze [alloy] materials used in conventional propellers. Due to the light weight of the propeller, however, propeller shafts can be manufactured with smaller diameters, contributing to a significant reduction in weight and fuel costs.

...During sea trials the CFRP required 9% less horsepower to operate compared to conventional aluminum-bronze propellers, and expansion of their use on merchant vessels is expected to contribute to better fuel economy and greater efficiency in operations...."

Pete

Anonymous said...

Hi Pete

According to NAKASHIMA PROPELLER CO., LTD, HDW has manufactured and tested composite propeller for submarine from 2002 and it currently is planning to equip composite propeller with 3.5m in diameter.

Propeller with hybrid structure consisted of metallic cavitation erosion resistant parts and light weight CFRP body seems to be possible. Blade tip which is to be exposed cavitation is covered by hard metal parts such as titanium nitride deposited titanium. Joint between metallic material and CFRP may be difficult.

Regards
S

Peter Coates said...

Hi S [at 25/6/16 10:04 PM]

Thanks for the information. For bare propellers and pump jets there seem to be so many materials technical advances and combinations.

I wonder whether there be increasing use of mostly carbon fiber reinforced plastic (CFRP) in bare propellers and pump jets. But to face wear/erosion by having quicker, more regular, replacement cycles?

Also what impact might battle damage/depth charging have on lighter (perhaps more delicate) CFRP propellers?

Interesting issue for us to speculate on the open source side while definite information on what exact materials propellers and pump jets are using, might be highly classified.

Reegards

Pete

Anonymous said...

Hi Pete

In terms of use under combat or sever cavitation condition, I do not recommend FRP (fiber reinforced plastics), because mechanical strength of matrix, i.e., plastic is too low. Instead, FRM (fiber reinforce metal), in which metallic material is used as a matrix, is recommended. As Aluminum matrixed FRM is relatively light, very strong/tough and non-magnetism, it is suitable for submarine propeller better than CFRP.

But, FRM has drawbacks such as being non-recyclable, very expensive and, difficult in production. Technology of FRM including ceramic fiber and production condition is one of the highest classified information.

Surface modified metal such as TiN deposited Titanium seems to be applicable. Drastically improved resistance against cavitation erosion resistance by TiN deposition, and non-magnetism and corrosion resistance by adoption of Titanium are expected. Problem of titanium is its high price, but, Titanium can be recovered from used propeller in contrast to composite such CFRP or FRM.

My conclusion is Aluminum-FRM > Titanium > CFRP

Regards
S

Peter Coates said...

Hi S

Thanks for that comment.

I would say as well as Titanium being expensive as a materiel - the specials skills/techniques and labour to shape it would be expensive.

Regards

Pete