Bow Chines - UK Astute Class Submarines

Discussion in 'Hydrodynamics and Aerodynamics' started by DCockey, May 24, 2014.

  1. DCockey
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    DCockey Senior Member

    The UK Astute class submarines have bows with sharp "chines". Anyone with a good guess or better about the reason for them?

    My understanding is subs generally operate with a slight bow-up attitude to generate positive lift. The "chines" could set the location where the boundary layer detaches from the surface and longitudinal vortices are formed.

    Page with photos of the bow: http://www.wired.co.uk/magazine/archive/2014/02/features/deep-dive

    More photos at: http://www.baesystems.com/slideshow/BAES_167167/artful-launch-gallery-module-1?_afrLoop=934594163000
     
  2. Eric Sponberg
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    Eric Sponberg Senior Member

    Hi David,

    Interesting picture--There is a statement in the article that alludes to the reason:

    And the shape of the boat is designed to reduce the signature of its wake -- which can be detected and followed up to 12 hours later.

    I'm also going to hazard some guesses about two other reasons: First, that the chines are there to simplify construction. Note all the flat panels on the sides--much easier to build than curved plates. Also, I bet part of it might be to reduce Sonar signature--with those flat panels (I am reminded of stealth aircraft with similar shapes) I can imagine that the sub would be harder to "see" by Sonar, what with sound waves NOT reflecting back to their pinging source.

    Eric
     
  3. Squidly-Diddly
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    Squidly-Diddly Senior Member

    My guess is it has to do with sub's sonar gear, and they need a flat surface to not distort sound waves (coming and/or going?)

    Maybe a special material that doesn't come curve yet.
     
  4. Mr Efficiency
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    Mr Efficiency Senior Member

    Secret Squirrel military business, maybe that is a dummy covering to conceal the "real" thing !
     
  5. PAR
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    PAR Yacht Designer/Builder

    With all the other edges on the exterior of that vessel, it doesn't seem to be an anti reflection type of element. With those planes and the tower, the modest amount of deflection the chines offer wouldn't amount to much. Busting up the wake seems more reasonable to me.
     
  6. SukiSolo
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    SukiSolo Senior Member

    Interesting beast to see under construction, though a fair bit of film of the first one afloat. Looks as if the angled underside may be more a blast deflection form from depth charges and mines. Some of the military road vehicles have a similar under shape to deflect IEDs'. Obviously it is combined with the other elements, wake minimisation, stealth etc.

    Interesting that 3D CAD 'translation' (presumably) problems cost £1 billion....
     

  7. tspeer
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    tspeer Senior Member

    If the chine has a hydrodynamic purpose, it may be to prevent asymmetric vortex shedding when the boat has an angle of attack. Asymmetric vortices can cause significant yawing moments.

    Besides having to do with its own sonar gear, it may be to avoid specular reflections from active sonar being used against it. As an attack sub, it is likely to be pointed at a hostile target when it is close enough for the target to be using active sonar, so the forward aspect is the most important.
     
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