Military recon powerboat concept

Discussion in 'Boat Design' started by Alex Alequin, Dec 19, 2006.

  1. kach22i
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    kach22i Architect

    The reason I was thinking axial fans are better than centrifugal fans for amphibious hovercraft (when considering heave acceleration) is that someone once told me axial fans have a flatter HQ curve.

    Some info here (non-hovercraft):
    http://ateam.lbl.gov/Design-Guide/DGHtm/fans.htm

    Example (non-hovercaft):
    http://ateam.lbl.gov/Design-Guide/DGHtm/centrifugalvs.vane.axialfans.htm
    [​IMG]
    Centrifugal vs. vane-axial fans
    Sometimes the less you know, the more open to learning you are. I'm an open book, tell me what you know.;)
     
  2. BMcF
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    BMcF Senior Member

    Mixed-flow and RD (radial diffuser) lift fans were proposed for several concepts (3KSES for example) that got a bit..er..obese as they approached final design completion stage. We now know from building many SES' since then that it was a pointless exercise for the most part. What I mean by that is that if you need fans that have higher pressure ratio than the HEBA centrifugal can deliver, yr already exceeding rational cushion loading ..and zee design will be a peeeg.;)
     
  3. kach22i
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    kach22i Architect

    I'm assuming that Mixed-Flow fans would of been considered as a compromised in between axial and centrifugal fans (best of both) and not as something to provide even more pressure than a centrifugal fan.

    What am I missing here?
     
  4. BMcF
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    BMcF Senior Member

    Mixed flow designs (witness turbochargers) are used to create higher delta-P across the 'machine' than can typically be achieved by purely radial centrifugal fans. That is a gross simplification that ignores so many other design factors...but one factor that seriously mitigates against using mixed flow whels is their complexity of construction. Airfoil centrifugal wheels are SO much easier to build.
     
  5. kach22i
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    kach22i Architect

    The rubbery plastic injected ones (vacuums and blow dryer type) are limited to what size and power?

    I'm building a scale hovercraft model, looking to use about a three inch diameter.

    Has CNC machining rewritten the rule book on what can be made and scaled up?
     
  6. BMcF
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    BMcF Senior Member

    You would know more about the scale fans than I probably. We use either axial muffin fans or FC (furnace blower or squirrel cage) types in the models we build...or a combination fo the two. The 57' radio-controlled 1/20 scale model SES that we are currently building has two 1.5 HP FC squirrel-cage blowers for lift air and 3 Rotron axial muffin fans to act as 'boost fans' for stern seal inflation.

    I'm partial to the FC fans for full-scale application as stern seal inflation boost fans. Great pressure rise and flow in a compact min-diameter package..not so great in efficiency but that gets lost in the 'noise' when you consider they average only about 15-20 HP each.

    As far as I know..all the mixed flow wheels are/were cast...
     
  7. kach22i
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    kach22i Architect

    I could find nothing on the second SES, but found this on the Gentry Eagle boat.

    FOR SALE:
    "Own a Piece of History. This is a rare opportunity to be the only person in the world privileged to experience the speed, adventure and prestige of owning Gentry Eagle."
    http://www.gentryeagle.com/

    The SES you are working on is over one thousand feet long?

    57 x 20 = 1,140 feet long................or is the model about three feet long?

    57 x 12 divided by 20 = 34.2" long?

    What good is 1/20th scale?

    I thought it had to be at least 1/6 scale to be of any use.
     
  8. BMcF
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    BMcF Senior Member

    1140 feet LOA..you got it! 1:20 is fine..1:6 is better..1:1 is best.:D

    Gentry and his team never got to finish the SES..the project collapsed when he went in to teh coma and never recovered.
     
  9. kach22i
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    kach22i Architect

    The 57' radio-controlled 1/20 scale model SES that we are currently building has two 1.5 HP FC squirrel-cage blowers for lift air and 3 Rotron axial muffin fans to act as 'boost fans' for stern seal inflation.

    Maybe my math is wrong; let's say a total lift of 10 HP assuming a useable 7.5 HP of lift, right? (1.5 x 5 = 7.5)

    I think 20 foot long hovercraft (not an SES) uses at least 20 HP for lift.

    Example:
    http://www.hovercraft.com/content/index.php?main_page=index&cPath=35_55

    Therefore, a 60 foot long hovercraft might be using 60 HP (I'll check an old Jane's Surface Skimmer's - 1976 or 1987, later).

    The SES uses 1/6 the lift which a fully amphibious hovercraft uses?

    I could believe 1/2 the power requirement, but 1/6?

    Is this more of a air assisted cat?
     
  10. kach22i
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    kach22i Architect

    Found this..........................no good pictures though.

    http://www.globalsecurity.org/military/systems/ship/hss.htm
     
  11. BMcF
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    BMcF Senior Member

    Yes..the air leakage is much lower for an SES than for an ACV. An since the leakage is mostly from the bow and stern, it is not greatly affected by increasing the cushioni Length to beam ratio by lengthening the cushion..thus this 10:1 L/B high-speed sealift 'thing' we are building has very low flow requirements for its size. We just completed a program review on the model build phase and I'll get some pictures posted up here soon. At 57' LOA, it is one of the larger remote-controlled scale models ever built.
     
  12. kach22i
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    kach22i Architect

    Largest I know of, including boats and aircraft.

    Your competition....................?

    SES pictures...................models too.
    Blyth Bridges Marine Consultants Limited
    http://www.blythbridges.co.uk/projects_column.html
    [​IMG]
    [​IMG]
    [​IMG]
     
  13. BMcF
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    BMcF Senior Member

    ah yes..my old friends Andy Blyth and David Bridges. Been quite some years since we worked together on some of those SES concepts.

    Our competition for..what?
     
  14. kach22i
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    kach22i Architect

    Model testing?

    Solving ride, stability and buoyancy issues for surface craft of unconventional design?

    I thought there was some overlap of services, my mistake?

    FYI:
    Right now I'm building a five foot long hovercraft model. It started out as a mock-up study for the cabin area only, and just to see if it would work as intended. I enjoy taking plan and section sketches beyond the 2D and into model form, real models (3D) not computer models.

    I kind of got carried away and now there is no turning back.:D

    I just picked up three (3") mixed flow fans from a vacuum cleaner repair shop ($15). I also picked up two (4") axial fans for thrust ($10) from an appliance repair shop.

    I have the electric motors and NICAD batteries from a few years ago and now have to make it all come together somehow.:(
     

  15. BMcF
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    BMcF Senior Member

    Sounds like a sweet model..and big. I like big..:D

    No mistake on your part..I just didn't know who or what you were referring to as far as competition. We have competitors..but few and we compete in a very small market. Collaboration is as often the case as direct competition..

    Our biggest source of work is supporting the 'big boys'..US and foreign navies and larger design houses and shipyards that don't have the expertise in-house to design and build the 'weird ones'..SES, ACV, SWATH, hydrofoils, cats, and hybrids thereof. Stabilization, or 'ride control' used to be our main specialty and primary business, but that morphed in to 'whole ship' design over the last 20+ years and now the ride control systems are a secondary part of our business today..even though we are one of only a handfull of companies worldwide that produce such systems.
     
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