Submarine Design Differences

[enigmaticuk]

I have asked this question on the forum previously but nobody had a definitive answer, so i pose it again.
What are the reasons for the difference's between UK and other naval submarine hull design? Most subs have a conventional streamlined cigar type architecture whereas the UK Astute and Trafalgar class have what i describe as a whale like appearance. The only explanations i can think of are stealth? streamlining? or something to do with sonar capabilities?
It always puzzles me when reviewing pictures, as if there is no advantage why use such a design? and if there is some advantage why is it not adopted by other naval architects?

 

[crobato]

What do you mean like a whale like design? Are you referring to the fact that the UK subs appear to have a straight ridge on top with the upper hull that is angled? I think the German and the Swedish subs seem to have it too, this straight, clean look. The latest Japanese designs seems to have gone into this direction as well. Whereas US, Russian, Chinese, and French designs continue with a rounded "body of revolution" look. Drawings of the Indian ATV and the Brazilian sub proposal also have the rounded cigar sub look. To be honest I'm not exactly sure what the reasons are, but I have some theories.

 

[enigmaticuk]

front of the sub comes to a oval point with a ridge in the conter, its hard to describe but i have posted some pics to compare. So what are your theories?

http://en.wikipedia.org/wiki/Image:Astute2cropped.jpg
http://en.wikipedia.org/wiki/Image:774_Virginia_rollout.jpg

 

[nevidimka]

I used to have the same curiosity as well. But my thoery is that both Americans/Russians and UK have different ways to achive the same result. Thats is quieting design tech. Altough it seems with the Russians they have a high reliance on Sonar absorbing material on thier hulls, n pehaps Uk does not rely heavily on these materials.

 

[crobato]

front of the sub comes to a oval point with a ridge in the conter, its hard to describe but i have posted some pics to compare. So what are your theories?

http://en.wikipedia.org/wiki/Image:Astute2cropped.jpg
http://en.wikipedia.org/wiki/Image:774_Virginia_rollout.jpg

To put it this way, the US has a very distinct submarine design tradition of its own.

The reason why US subs have a round nose is because the entire front nose is housing a spherical sonar. And that's why you also don't see torpedo tubes on the nose like you do with Russian subs.

The Russians like to put their torpedo tubes in the front of the nose in the upper hemisphere. The bottom hemisphere, they put a large cylindrical sonar.

On the Astute's nose, I have a hard time seeing that nose having a spherical sonar. For me, it looks like a tall cylindrical sonar. Boy, the sub seems to hav awfully big flank sonars.

 

[Gryphon]

Performance is not always the master ...

Production costs weigh heavily on a design as well. American and Russian subs are usually designed with the intent of large production runs. Hull sections of the US 688 class, Seawolf and Virginia class vary in beam (33, 40 and 34 foot respectively), but are the same basic shape. Tooling, manufacturing techniques (welding equipment), analysis models, all benefit from the economy of similarity for design and manufacturing. British sub classes are not exactly one-offs, but certainly have a lower quantity expectation.

Russian Alfas and Akulas are roughly similar (tilt your head sideways) but they tend to simplify their hulls because of double hulls - creases are more difficult to make like that. Also, rounded shaped are more efficient in dispersing pressure loads. The deeper the sub's mission, the more rounded the hull section. Creases also create pressure boundaries at speed, ie cavitation and noise.

The bulbous very rounded noses are to equalize sonar performance, creases would be difficult to map into the sonar s/w.

The British Astute hull design is curious. Perhaps they are relying on lateral sonar arrays only, or have minimized the forward array. The pointed prow is suggestive of a desire for better surface performance, but that seems unlikely considering their mission.

Just speculation on my part, watch a Naval Engineer rip my guess apart...

 

[crobato]

The question centers on the nose, which is going to be composite any way, and its more sensor related in the manner of design. If there are no sonars in the bow of the Astute, the torpedo tube openings would be right in the knife of the bow, WWII sub style. Instead, the tubes are all drawn back, so there has to be a sonar in the bow, and it has to be shaped like a tall cylinder, like a thermos bottle.

US subs are single hulled, while it seems in paper, less labor, the pressure hull has to be shaped hydrodynamically. That requires some very powerful machinery to do, to bend tough pressure plate into a smooth form. Double hull is more manually extensive, but the tough pressure hull which is the inner hull, does not need to be shaped. The plate for the outer hydrodynamic hull can be much thinner and much easier to bend. In any case, all these is besides the point when it comes to the nose, since the hull really starts on the back of the nose.

 

[gf0012-aust]

Altough it seems with the Russians they have a high reliance on Sonar absorbing material on thier hulls, n pehaps Uk does not rely heavily on these materials.

I don't think so. Russian acoustic matting technology has been an unmitigated disaster. Poor design, poor placement and poor sealing.

Getting the hull shape "right" (as such) is early submarine generation engineering concepts, that design philosophy was replaced and companioned almost a decade ago by other solutions.

signature transmission is relative to design mission and all the variables that get thrown into that mix.

btw, simplistically flank array mass is closely aligned to on board power, the brit subs are "pumping" out sufficient power like nobodys business....

 

[s3kiz]

Production costs weigh heavily on a design as well......Tooling, manufacturing techniques (welding equipment), analysis models, all benefit from the economy of similarity for design and manufacturing.

Russian Alfas and Akulas are roughly similar (tilt your head sideways) but they tend to simplify their hulls because of double hulls - creases are more difficult to make like that. Also, rounded shaped are more efficient in dispersing pressure loads. The deeper the sub's mission, the more rounded the hull section. Creases also create pressure boundaries at speed, ie cavitation and noise.

The bulbous very rounded noses are to equalize sonar performance, creases would be difficult to map into the sonar s/w.

The British Astute hull design is curious. Perhaps they are relying on lateral sonar arrays only, or have minimized the forward array. The pointed prow is suggestive of a desire for better surface performance, but that seems unlikely considering their mission.

x2

I was about to post a comment about the shape variances we see in subs, much like with the above ideas, but having read Gryphon's post i can only congratulate him for his, very well put.

Cheers.

 

[stuuu28]

Chin Mounted Sonar

ISTR that the Asute has a Chin mounted array.

The NavyMatters site has some good pics of the space it fits into. Its not inside the hull like on US subs.


Must be using a very different tech than the US subs

 

[Gryphon]

Rolling vs forming

Thanks s3kiz.

I'm a manufacturing engineer <<big shock there>>, and have run a production line for rolling 3.5" thick steel plate and then welding it.

American long tube designs are classical, steel tubes with composite forward caps (sonar domes). Making a tube from plate is easy, plate rolls have been with us since the start of the industrial revolution. Forming heavy steel into complex 3D shapes is mind bogglingly expensive, difficult and fraught with dangers.

Submarine hull steel is tough stuff [a parallel discussion here somewhere]. The stronger the material, the more inherently resistant to forming it is hence the simpler shapes.

 

[crobato]

If you check the Astute, you can see a long line, a limber hole line, that marks the main hull and the upper hull. The line stretches from the bow cap all the way to the rear.

Its not hard to imagine that the main hull is built like a rolled cylinder. No different fundamentally to the US sub. But the difference is that an additional hull is built on top of this cylinder, which has the angled sides and ridged top. The space between is made into buoyancy tanks.

US sub designs are long tube but about two thirds or so to the rear, the tube is waisted and funneled into a smaller tube, then funneled back into a larger tube again. The differences in width and diameter between the main hull and the waist is then covered with an outer hull to make a continuous hull form. The space within is made into buoyancy tanks.

The Soviet sub designs can be compared to a cigarette built inside a cigar. The cigarette, which has a long cylindrical form, makes up the inner pressure hull, while the cigar makes up the outer hull. The space in between is made into buoyancy tanks.

 

[gf0012-aust]

US sub designs are long tube but about two thirds or so to the rear, the tube is waisted and funneled into a smaller tube,

mate I've been to the Seawolf and Virginia Program and Development sessions that were given by the builders and co-sponsored by CINCPAC a few years back - and they aren't built like that.

 

[nevidimka]

Why is the difference in US,western building concept of the sub compared to Soviet thingking?

What are the advantages n disadvantages of each style of construction?

 

[davros]

From what i have read the British have designed there submarines with noise reduction as the no1 priority, The Russians design priority is speed, and the American principal is between these 2 points producing subs that are not as silent as the British units but not as quick as Russians. I cant remember what book i read that in though.

 

[rabs]

From what i have read the British have designed there submarines with noise reduction as the no1 priority, The Russians design priority is speed, and the American principal is between these 2 points producing subs that are not as silent as the British units but not as quick as Russians. I cant remember what book i read that in though.

A quick glance through wiki (not a great source but sufficent for this purpose) shows no measuable speed difference between Russian and US subs. An Akula has 2 knots on a 688I, and probally cant travel at similar speeds without cavitating.

So if the Russians are sacraficing noise levels for speed, they are doing a terrible job.

 

[crobato]

Why is the difference in US,western building concept of the sub compared to Soviet thingking?

What are the advantages n disadvantages of each style of construction?

Its a challenge to answer in a nutshell some of their notable differences.

US: Started with double hull design but sometime afterwards switched to a single hull design from the Skipjack onwards. USSR: Stayed with double hull design.

West: Shifted from double shaft, double screw designs to single boresight shaft, single screw designs in all submarine types. USSR: Although it took longer, finally did the same except on SSBNs, where they remained double shafted, double screwed. Until the Borei class that is, but the Borei is post Soviet Union.

Reactor: West: By far single reactor designs with few exceptions like Triton class. USSR: SSBNs are all double reactor. SSNs started with double reactor designs then shifted to single reactor.

US in particular from Thresher class onwards: Uses spherical sonar dominating the nose dome. Torpedo tubes are moved elsewhere. Seawolf added chin sonar with spherical sonar. USSR: had the standard layout with torpedo tubes on the upper half of the dome and the chin cylindrical sonar on the lower half of the dome. Allegedly moving to a spherical sonar design but that would be post SU era.

On diving planes, both started with retractable ones in the hull. From the Skipjack to the early LA class, the planes are moved to the sail. From the 688I onwards, moved back to the hull. The Soviets always had their planes in the hull except for the Delta class. SSKs are a different matter as they have another reason of moving their planes to the sail which has to do with flank sonars---hence why SSKs trended to put planes in their sails as the nukes kept them to the bows (Artic ice breaking among other reasons).

On the sails, the US seems to prefer fairly squared designs. The USSR is divided into two camps. The Malachite bureau likes streamlined, flaired sail designs while the Rubin bureau likes them squared too.

Towed array. In the West, sometimes they're pulled from the hull, either top, underneath or the side using a sleeve. The Russians like to pull them from a tail extension on top of the upper vertical fin.

Limber holes. The USSR likes them in lines of holes, while Western designs prefer slits.

Cruise missile: The US has them vertically launched, the USSR has them on an angle. The Klubs are VLS but they're post Soviet Union.

As an added note, the Western nations also have some differences between each other, like between the French, US and British nukes. Western SSKs also seem to differ in their approach, e.g. Scorpene vs. Type 212.

 

[gf0012-aust]

From what i have read the British have designed there submarines with noise reduction as the no1 priority, The Russians design priority is speed, and the American principal is between these 2 points producing subs that are not as silent as the British units but not as quick as Russians. I cant remember what book i read that in though.

considering the fact that the USN and NAVSEA had to step in to provide assistance to help resolve problems with the Astutes, then I'd suggest that your book is a little way off the mark on facts.

the problem was so significant it resulted in a report to SecDef and USN and triggered a similar report into Australia.

 

[davros]

This book was 20 years old so it may well have changed since then, Plus it may well have been inaccurate. I remember going on board some old Russian sub and it was amazing how far behind it looked inside compared to an equivalent British sub that i went on.