Wave piercers

Discussion in 'Hydrodynamics and Aerodynamics' started by ShaneK, Feb 21, 2018.

  1. Mr Efficiency
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    Mr Efficiency Senior Member

    I'd imagine that any even minute surface wake evidence that well submerged subs create, and can be detected, is top-secret intel.
     
  2. fastsailing
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    fastsailing Junior Member

    There are civilian subs too for tourists. I doubt any observable fact any tourist inside looking up through the glass roof/ceiling can see, would be a top-secret.
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    I think we have a small misunderstanding here, I was trying to say that if deeply submerged subs leave any kind of perceptible surface disturbance, it would be of immense interest in anti-submarine warfare. And I don't think we'll be told about it.
     
  4. fastsailing
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    fastsailing Junior Member

    Perceptible to a human eye or some high tech sensor?
    How deeply submerged?
    Is the surface of the sea totally calm or is there waves due to wind?
    If some sensor could detect surface disturbance in totally flat calm conditions when a sub passes for example 50 meters below surface, but could not tell the difference of that and a disturbance caused by a small fish 1 meter below surface, would it be of any military value at all?

    It seems to me any sub no matter how deeply submerged will cause pressure differentials along its surface when moving. If the air pressure at the sea surface does not change, there will be a pressure gradient acting on the water above the sub that is not there elsewhere, causing the large mass of water to accelerate. It's only a question of just how small effects can be observed, rather than if those effects exists. And even if they can be observed it's a matter of separating those from other numerous causes of local sea surface elevation chances. My guess is both reasons alone would make such detection attempt impractical.
    And stealth of military aircraft is not about not being detected at all. It's enough not to be shot down due to not being located accurately enough by those low frequency radars capable of detecting stealth planes. Same principles could apply to subs even if they were detected by some sensor in some rare conditions.
    To be of interest for anti-submarine warfare would require being able to detect reliably at least most of the time, not once in a year during one second time period.
     
  5. BMcF
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    BMcF Senior Member

    The US and Russian (or, previously, Soviet) navies have invested considerable time and money in developing very accurate non-acoustic submarine detection methods based on surface "scars" and other observable wake effects created by deeply submerged submarines. The Russians were even reported to be developing an ASW weapon system that used that information for direct targeting, but no confirmation it was ever deployed.
     
  6. BlueBell
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    BlueBell Ahhhhh...

    Holy thread drift Batman!!

    Anyone notice the OP is long gone and ... what are we talking about???

    Oh right, Wave Piercers...
     
  7. BMcF
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    BMcF Senior Member

    *chuckles*....it happens.

    I have a good bit of direct experience with waver piercing cats...but only the powered kind. ;-)
     
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    This is what I was alluding to, I think my Finnish correspondent was more focussed on what the human eye could detect, though. Like all things where military secrets are involved, disclosure will be lacking. I often wonder whether the failure to detect the missing 777 in the Indian Ocean, reflects a reluctance to deploy technology that might be able to find it, but also "give up" the level of detection capability available.
     
  9. BlueBell
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    BlueBell Ahhhhh...

    I believe you are fear-mongering and catastoihpsing a non existent situation regarding government secrets.


    Furthermore, form-wave distortion can be adequately detected with the human eye for the level of accuracy required in this thread.

    However, it is not necessary as it has already been established; three submarine diameters worth of depth is an accepted minimum.
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    lol...…The catastrophe was when it disappeared, whether the effort to actually find it is all-stops-out, I am entitled to wonder about, I certainly believe it to be an open question.
     
  11. fastsailing
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    fastsailing Junior Member

    Sure, all things can be investigated and even weapons systems developed, but we do know one thing for sure:
    All countries having nuclear subs carrying ICBMs continue to build them and using them. That tells us any weapon system there might be is not believed to be very good accomplishing its mission, because stealth of subs are still considered far better than placing all those ICBMs on a less costly surface ship with all the modern defense systems known to counter any attacks.
    Therefore I still conclude that it doesn't matter that exact capability of sensors in detecting subs are top-secret, because using simple logic overrules that problem. Stealth counts and detection systems fails most of the time. Meaning that even if some sensor placed on a satellite could detect a sub if looking on the exact correct spot at the correct time, it can't do that for all the vast area of oceans to find the sub in the first place to track it.
     
  12. fastsailing
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    fastsailing Junior Member

    Back to the subject of wave piercing:
    Wave-piercers - marketing myth or design ingenuity? https://www.boatdesign.net/threads/wave-piercers-marketing-myth-or-design-ingenuity.30296/page-5#post-348013
    A little bit over 8.5 years ago BMcF, who in my perspective looks to be are real world expert on the subject of control systems for wave piercers, wrote:
    I think that was and still is correct statement, but does the control system have to be active?
    Most aircraft do just fine with passive stabilizers at the tail shifting aerodynamic center aft of the center of gravity and thus providing static stability.
    Is there any reason why a fast power catamaran with narrow waterlines and center of flotation aft and reduced reserve buoyancy near bow ( not including reserve buoyancy of another airbourne "hull" at the centerline due to assuming it stays airbourne) called wave piercers would not respond to the same way as aircraft for adding a passive horizontal stabiliser to the "tail" or in this case called transom or stern?
    Does the same also apply to SWATH?
    Is it just that active systems are far better or is there a reason a passive foil could not do the job when wave encounter frequency and natural pitch frequency are the same causing resonance with the hopefully known results?
     
  13. Ad Hoc
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    Ad Hoc Naval Architect

    Just not as well, as passive would provide just damping alone.

    Depends upon the speed of the Swath and, if it is dual role...ie slow speed and high speed.
    But it is better being active.

    It really depends upon the LD ratio of the hull and, more important, its natural frequency and how it compares to the expected encounter frequency.
     
  14. fastsailing
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    fastsailing Junior Member

    What else does active system do than providing a force resisting motion of the "tail" defined as damping and why?
    Or are you just referring to the fact how magnitude of force depends on local vertical speed of the damping foil, and that being possibly different in passive vs active systems due to active pitch angle changes for the foil relative to the ship?
    If that is the case then the passive system could do the same damping by having a larger area foil with more viscous drag as a result, and active system avoids that by consuming some small amount of energy for active pitch control using higher angle of attack for the smaller foil area to achieve the same pitch resisting lift force with same induced drag but less viscous drag.
     

  15. Ad Hoc
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    Ad Hoc Naval Architect

    Well, you’ve got it in essence.

    A passive foil will provide damping and reduced the amplitude of motion. No matter the response it encounters….it is “part” of the part as such. But a “one” time event with each passing wave, as such.

    An active system will also provide a ‘counter’ restoring force in real time to the response. And the restoring force of any vessel is proportional to its GM. So high stiffness vessels, like catamarans, have large GMs, so they need large foils, that create the lift (force). But the high stiffness means very large foils which equals law of diminishing returns, since the larger the foil(s) the greater the drag too. Not to mention the forces required on large catamaran are not small at all! Whereas on a vessel with a low GM, like a Swath, it is very easy to restore the motion. But, for both, this is in real-time, so not a one time event. The motion control system constantly monitors the attitude of the vessel and corrects it; the foil(s) altering their AoA to produce the forces required.
     
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