• Hi Guest! Forum rules have been updated. All users please read here.

Astute submarine

Ronny

CLEARANCE: Secret
Joined
Jul 20, 2019
Messages
257
Reaction score
107
I have tried to research but can't find relevant information anywhere, does anyone know why the Astute class have very strange nose shape?
Astute:


Normal submarine
 

Foo Fighter

I came, I saw, I drank some tea (and had a bun).
Joined
Jul 19, 2016
Messages
1,458
Reaction score
459
These things evolve all the time I think the teardrop shape is going out of fashion for a while, apart from possibly high speed types.
 

Ronny

CLEARANCE: Secret
Joined
Jul 20, 2019
Messages
257
Reaction score
107
These things evolve all the time I think the teardrop shape is going out of fashion for a while, apart from possibly high speed types.
I highly doubt that, among the modern submarine, only Astute doesn't have the tear drop shape I think.
 

Moose

CLEARANCE: Top Secret
Senior Member
Joined
Jul 4, 2010
Messages
1,249
Reaction score
233
American SSNs use a large composite fairing over the bow which is optimally shaped for smooth flow at speed. The bow sonar(s) sit inside this fairing, and the steel starts with the bulkhead behind that sonar. Both the large spherical sonars used before Virginia block III and the more modern arrays, therefore, make some compromises to the bow's need for streamlining. Royal Navy SSNs are steel all the way out to the bow, the sonars are arranged in arrays which sit in "windows" set in the steel structure. These arrays cannot (affordably) accommodate complex curves like those required for a USN-style bow, and the RN doesn't want to set them within a large composite fairing like the USN uses. So, the bow they use is their solution to get optimal sonar performance while streamlining as much as possible.

In very broad strokes, the RN claims their compromise results in better sonar performance, especially at low speed, while the USN claims better hydrodynamic performance and less sonar degradation at higher speeds. The comparative real-world performance of the two navies sonars is the sort of thing you'll only find in the classified realm.
 
Last edited:

Ronny

CLEARANCE: Secret
Joined
Jul 20, 2019
Messages
257
Reaction score
107
American SSNs use a large composite fairing over the bow which is optimally shaped for smooth flow at speed. The bow sonar(s) sit inside this fairing, and the steel starts with the bulkhead behind that sonar. Both the large spherical sonars used before Virginia block III and the more modern arrays, therefore, make some compromises to the bow's need for streamlining. Royal Navy SSNs are steel all the way out to the bow, the sonars are arranged in arrays which sit in "windows" set in the steel structure. These arrays cannot (affordably) accommodate complex curves like those required for a USN-style bow, and the RN doesn't want to set them within a large composite fairing like the USN uses. So, the bow they use is their solution to get optimal sonar performance while streamlining as much as possible.

In very broad strokes, the RN claims their compromise results in better sonar performance, especially at low speed, while the USN claims better hydrodynamic performance and less sonar degradation at higher speeds. The comparative real-world performance of the two navies sonars is the sort of thing you'll only find in the classified realm.
Thank you, this is the kind of answer I was looking for.
 

Foo Fighter

I came, I saw, I drank some tea (and had a bun).
Joined
Jul 19, 2016
Messages
1,458
Reaction score
459
These things evolve all the time I think the teardrop shape is going out of fashion for a while, apart from possibly high speed types.
I highly doubt that, among the modern submarine, only Astute doesn't have the tear drop shape I think.
Just pointing out that we are not at the final form of the submarine and more 'different' designs are likely to crop up.
 

Hood

CLEARANCE: Top Secret
Senior Member
Joined
Sep 6, 2006
Messages
1,789
Reaction score
1,068
The shape goes back to the Swiftsure class, the Astutes just having a refined and very noticeable form of it. Doubtless a lot of work would have been done at the testing tanks at Haslar.
 

Foo Fighter

I came, I saw, I drank some tea (and had a bun).
Joined
Jul 19, 2016
Messages
1,458
Reaction score
459
With what we paid for it, I do hope so.........
 

totoro

CLEARANCE: Secret
Joined
Jan 11, 2011
Messages
337
Reaction score
56
Website
www.youtube.com
I am not sure I understand the explanation above. But let me try to rephrase it, to see if I got it:
So, US subs use a bow shape optimize for speed.
That shape can be achieved only with composite bow, if one wants a sonar of sufficient size.
British subs don't use that shape as the composite bow is too expensive for them. (really? in the context of a multi billion dollar sub? How much is the composite bow then, half a billion?)
British subs then use a smaller sonar, which resides in the lower half of the bow. So only that lower half cover is composite, while the upper section is metal.
Somehow the british bow shape is better for sonar performance at lower speed. (How?) Is the visible chine the reason for that?

At the same time old russian subs had a similar solution to Astute, with lower half of the bow being for sonar.
Newer russian subs have more similar bows to US subs, with torpedo tubes moved to the side and sonar cover accounting for the most of the bow.
Yet no russian sub have the chine.
No other (non british) sub in the world has the chine.

I am failing to see the connections here - just how is the speed and sonar influencing the decision to include a chine?
 

Ruriruri

CLEARANCE: Restricted
Joined
Nov 10, 2019
Messages
6
Reaction score
2
Another thing to remember with British boats is that they tend to be more specialized for Arctic and ASW missions, they’re willing to settle for a shorter design service life vis a vis cost, and, particular to the Astute, they had to design an attack boat around a missile boat reactor.

Similarly, while the Virginia class can (technically) do (some) Arctic missions, it doesn’t have a hardened sail and is more limited in that respect compared to its predecessors. Here’s a 2013 summary on some Virginia class testing they did on Arctic and special warfare capabilities. Given that what I’ve read in more recent years has the Seawolves playing around in the Arctic I’m guessing a renewed emphasis on Arctic and UUV capability is why SSN(X) resembles Seawolf.

What I’m trying to get at is a given design can vary greatly depending on mission profile, design service life, and external cost and political factors.
 

Attachments

major-1

2 Form
Joined
Jan 4, 2017
Messages
15
Reaction score
9
This design is adopted to counter active sonars of ships and helicopters. The hanging structure above the sonar absorbs the signal
 

Trident

CLEARANCE: Top Secret
Senior Member
Joined
May 8, 2006
Messages
964
Reaction score
173
I've been wondering about this too and think Moose could be onto something, but I'm not certain.

So, US subs use a bow shape optimize for speed.
Yes, more specifically for smooth flow around the sonar dome at high speed, resulting in less degradation of sonar performance in this regime.

That shape can be achieved only with composite bow, if one wants a sonar of sufficient size.
No. As you say, legacy Russian subs have long adopted a similar axisymmetrical bow shape that, as on their British counterparts, is steel apart from the composite sonar windows. So that's not the problem.

British subs don't use that shape as the composite bow is too expensive for them.
No, cost isn't the obstacle, very strong emphasis on good sonar performance at low speeds is claimed to be.

Somehow the british bow shape is better for sonar performance at lower speed. (How?) Is the visible chine the reason for that?
Flow noise is less of a concern in this regime, perhaps making refractive distortion from a non-optimal sonar dome geometry relatively the more pressing consideration. The sonar window on Astute appears to be single-curvature while an axisymmetric dome would obviously be double-curvature. Now, unless the surface of the sonar can match the window shape however, the distance between it and the window, as well as the thickness of the window material traversed by the sound waves, is not uniform in all directions.

At this point it is worth noting that the bow sonar array configuration hitherto employed by US, Russian and British subs is different. Russian SSNs used to be fitted with cylindrical or conical bow sonars, US submarines famously adopted spherical arrays whereas British sonars were always what is known as conformal arrays. This latter technology has now also been adopted by the LAB sonar for the Block III Virginia-class and possibly all but the first (which has a US-style spherical array) Russian Severodvinsk-SSNs, following its introduction in the Lada-class SSK. There is potentially a significant difference though: both the US LAB and the Russian Lira sonar surfaces are double-curvature, while based on the sonar window the British arrays may well be single-curvature (two inclined planar panels joined by a cone frustum section at the forward end). This simplification could explain why the British were able to go down this route so early, at the cost of having a rather unorthodox bow shape forced upon them to make it work. Now that such arrays can be successfully implemented with double-curvature surfaces and therefore made to conform to favourable high-speed bow geometries, the US and Russia (having previously baulked at the shaping restrictions) are adopting this solution too. The British meanwhile, for cost reasons, are sticking with a bow configuration that has served them well enough for decades.


The one outlier which doesn't quite fit into this picture is the British Vanguard-class SSBN with its axisymmetrical bow. A surprising departure from convention (given that high speed is less relevant for nuclear deterrence role) and if it has a double-curvature conformal sonar why wasn't this technology later adopted for Astute?

A long winded way of saying I don't bloody know either, I guess :)
 

Moose

CLEARANCE: Top Secret
Senior Member
Joined
Jul 4, 2010
Messages
1,249
Reaction score
233
The Vanguard bow is something of a hybrid, and is unique to the class' sonar suite. It's closer to an American-style bow than is usual, I don't know enough about RN internal workings to say why they went that way rather than following their usual practice, but it seems unlikely they will do so again.
 
Top