New Hovercraft design change ?

Discussion in 'Boat Design' started by DocScience, May 28, 2011.

  1. BMcF
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    BMcF Senior Member

    You have already sketched most of that in your cartoons of the concept. An array of panels side by side and hinged at the wet deck. In the most succesful incarnation we ever tried, the panels (2 meters in width each, if I recall, and approximately 4 or 5 meters long..we are talking about sealing the air cushion on a 35m SES) were built using sandwich-cored FRP construction methods and supported (pushed downward) via Firestone pneumatic air springs, one for each panel. The pressure was adjustable and 'tuned' based on direct observation of the seal panel dynamic behavior through a porthole installed to view the air cushion interior.

    The design survived over 1000 nautical miles of rough water travel at 40 knots average speed before it came apart.
     
  2. DocScience
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    DocScience Wishful builder

    Using the terms that BMcF mentioned, I was able to do a search and came up with this.
    Other people here, have said something somewhat similar, but I found this wording interesting and rather blunt.

    http://www.mckesson.us/mckwiki/inde...sign_of_Advanced_Marine_Vehicles_-_Chapter_18

    " Early rigid skirts consisted of simple hinged plywood panels fitted at the bow and stern of an SES. The first generation of this simply hinged the panel at the top with a door hinge. The problem is that the cushion pressure acting behind this panel results in a large force, and simply makes the panel into a plow, eliminating the resistance advantages of the SES. "


    I am still hoping that BMcF can give me a sketch of some rear skirts that failed.
     
  3. BMcF
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    BMcF Senior Member

    What's to sketch that was not described? Chris ended that section of his textbook (of which I was a reviewer when he first wrote it..;-) ) quite properly in my opinion.

    :cool:
     
  4. DocScience
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    DocScience Wishful builder

    BMcF

    I guess I was posting at about the same time you were.

    You gave me a very good description. Thankyou.

    The only thing that I am wondering about, is that I am proposing that extra rear skirt, which takes a lot of pressure off of the inside rear plate, but the inside plate still needs some springs, but not nearly as much.

    Do you know if they tried extra rear flexible skirt in this arrangement that I describe ?
     
  5. BMcF
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    BMcF Senior Member

    Your concept is essentially the same in basic terms to the multi-lobe stern seals in use today...the only difference being that your forward seal face is envisioned as a non-flexible panel and the seals currently in use have the flexible fabric-reinforced rubber forward face instead.
     
  6. kach22i
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    kach22i Architect

  7. Jeremy Harris
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    Jeremy Harris Senior Member

    As a boring aside, I was the one who signed off the business case for PACSCAT around 5 years or so ago. I was the Ops Director of the organisation that procured UK defence research at the time. I well remember questioning the prior art on some of the claims being made, and mentioning the fact that some of the features being claimed as novel most probably weren't. I strongly suspected that there was political pressure being brought to bear by the research contractor at the time, and personally I wasn't wholly convinced that this technology demonstrator had as much merit as was being claimed. On balance it was good enough to be worth doing, but I still harbour doubts as to whether we'll see a new SES landing craft in service any time in the next 20 years.
     
  8. BMcF
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    BMcF Senior Member

    The hull form of the PASCAT is quite different to previous SES designs and the overall performance envelope is intentionally different; a very key difference being that, unlike the Norwegian SES for example, the PASCAT is not at all intended to be a good 'open water seakeeping speed machine'. What it brings instead is low draft,a decent payload capacity and a 'higher' top speed than conventional small-to-medium sized landing craft. There is a lot of interest in that here in USN too..the PASCAT is viewd as a 'niche' player falling between the exotic high-end and low-payload LCACs and the large, slow, heavy lift LCMs and the like.

    But PASCAT bears little resemblaance to other naval SES like the Norwegians and Russians now operate or had operated in the past.
     
  9. Jeremy Harris
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    Jeremy Harris Senior Member

    Yes, I did read the business case before signing it, so am pretty much aware of the particular aims of this technology demonstrator. The problem for me is that, in a time when we have severe pressure on public sector budgets (and defence in particular) I wasn't convinced that we should be investing very limited research funding in this area. PACSCAT represents a sizeable hunk of our very limited research budget, at a time when it was being sliced by another 20%. I'd have rather seen the money go on force protection, to reduce the number casualties we continue to get in all the peace keeping/intervention activities that we seem to be interminably involved with.

    Maybe I'm wrong, and we'll have an enduring need for a fast landing craft. Somehow I doubt it, as every war fighting scenario we seem to get involved with needs more helos, reconnaissance assets, heavy lift and specially trained (and well equipped) ground forces. I can't recall when we last used a large landing craft based force. It wouldn't surprise me if it were as long ago as the Falklands..........
     
  10. BMcF
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    BMcF Senior Member

    On this side of the pond there is extensive argument too about whether we really require "amphibious assault groups" and all that entails in specialized ships and craft. Critics always start out by noting that the last time the US conducted an amphibious assault, Doug McArthur was in charge of it.;)

    Me..I'm a humble designer of oddball ships and craft and not an expert in Naval reqts and CONOPS. As such, I too often (OK..always..) root for whatever team wants to build the kind of ships I design. :D
     
  11. DCockey
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    DCockey Senior Member

    My understanding is the US Navy's primary interest in SES vessels in the 1970's were as combat vessels, not as landing craft or the like. The SES100A and SES100B were certainly not amphibious nor was the experimental SES boat the Naval Acadamy built. The planned 3000 ton SES ship was intended to be a high speed combat vessel and an intergral part of the 100-knot navy Admiral Zumwalt promoted.
     
  12. BMcF
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    BMcF Senior Member

    You are correct. The 100-ton craft (and several others) were development models for the future fast frigate SES that was envisioned. And the PASCAT is not amphibious either..just beachable. I'm note sure where any confusion on that point might have arisen from.

    The only truly 'amphibious SES' concepts came out of the recently completed ONR T-craft program. But those concept designs were all both SES and ACV..transforming completely between one type and the other. But there was arguably more service interest in the SES mode of the competing designs, as long as that craft was beachable, capable of extracting itself from the beach without assistance, and could offload/onload with organic ramp capability. All the extra complexity and equipment required to transform in to fully amphibious mode..not so popular.
     
  13. DocScience
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    DocScience Wishful builder

    This is Version number 3.


    I have added a "flexible front skirt" , which is attached to the "rigid front skirt" .
    This makes it possible to reduce most of the air pressure on the "rigid front skirt", and this will reduce the amount of plowing that the "rigid front skirt" will do.
    By changing the position that the "flexible front skirt" is attached, it is possible to vary the amount of air pressure on the "rigid front skirt", to whatever is desired.
    The "rigid front skirt" can be made a partially flexible front skirt , as desired.


    The same situation can be done to the "rigid rear skirt" .
    By varying the position of the "flexible rear skirt", it will put downward pressure on the "rigid rear skirt" , as desired, and no spring will be needed on the "rigid rear skirt".

    The connection arrangement positions will need some adjustment, but I wanted to explain my main theory here.


    It is possible that I have screwed up my physics , due to the late hour, but if so , I am sure someone will tell me.
    .
     

    Attached Files:

    Last edited: Jun 1, 2011
  14. kach22i
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    kach22i Architect

    If you can quickly control and regulate the pressure in the triangular zero pressure rigid front flat area, you may be able to control heave.

    A negative pressure in this same area could suck up the front panel if enough to counter the force applied to the lower area of it.

    A positive pressure greater than the surrounding forces could force it downward.

    Advance ride elements are BMcF's territory, not mine. Just thinking out loud.
     

  15. DocScience
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    DocScience Wishful builder

    The front top triangular area would most likely have an opening to the top, to stay unpressurized.
    Does anyone have suggestions or other ideas about this ?
     
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