Why Are SWATH Tubes So Long?

Discussion in 'Boat Design' started by zstine, Sep 16, 2021.

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  1. Ad Hoc
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    Ad Hoc Naval Architect

    That'll give you around 1.8 tonne for all consumables/variables... including ballast.
    Can't see that happening..

    You're missing the point. The tubes carry the buoyancy.
    If you wish to use fins for lift (makes no sense), they will need to be very large - considering your expected speeds = lots of drag.

    For your length, that's right on the hump = even more drag.

    Sorry, it is just a wish list not rooted in any hard data.
     
  2. zstine
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    zstine Junior Member

    Where did the 1.8 tonne come from? what if I said the light ship was just 12,000 lbs?

    I guess I am missing something. In this concept, as in the HYSWAS 'Quest', the tubes do not carry full buoyancy. The superstructure is waterborne at rest and lifts off at speed. In the proposed design, the fins only need to lift 30-40% of the displacement, so can be relatively small compared to a hydrofoil boat. And similarly the tubes are smaller than a SWATH tube since they are at 60-70% displacement.


    Again I'm missing something. Submarines don't have a drag hump that I'm aware of. Hydrofoils have drag humps because the hull is in the water until lift off, then drag drops as you get foil borne. there's negligible residual resistance in this design. so I would expect a hump at less than 4 knts when the hull is waterborne. Above that, as BMcF said who has first hand HYSWAS knowledge, "there is no hump" (he states that in the "HYSWAS anyone" thread). "The drag just increases with speed". Where does this hump at 10knts come from?
     
  3. Ad Hoc
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    Ad Hoc Naval Architect

    Hmmmm....:confused::confused:
    I think JEH summed it up best:

     
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  4. jehardiman
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    jehardiman Senior Member

    Can't be done with a SWATH of existing construction. Sorry, but just read the references to know why.
     
  5. zstine
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    zstine Junior Member

    Haha. Good thing I didn't propose a SWATH! It's a HYSWAS (hydrofoil small waterplane area ship) and it exists, so very much possible... now practical is a separate story. And I'm sure my power numbers are off, but that's why I'm here.
     
  6. Ad Hoc
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    Ad Hoc Naval Architect

    Then you need to DESIGN it.. rather than just looking at endless research papers.
    Draw it, to scale, see what fits what doesn't fit.

    Then, and ONLY then, can you start to establish the weights.....to arrive at the lightship and then full load.

    Once you have that, then you can establish the hull form, whatever it maybe, to satisfy the weight of the design to float where you want it to float.
    And of course check the basic statical stability too...

    And then... you can finally establish the power requirements.

    Until you do the above.. it is just lots of bandwidth about hot air...
     
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  7. kerosene
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    kerosene Senior Member

    dunno. I mean the reading list is valid but otherwise isn't this a design forum and his questions are reasonable and well formulated.

    Q: "how does airplane work?"
    A: "very smart people have designed them to work. It's all very complicated."
     
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  8. Ad Hoc
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    Ad Hoc Naval Architect

    A:- which part of it’
    Q: all of it..
    A:- how long have you got..?
    Q:- why?..it is a simple question how does it work
    A:- ok, cancel your social life for the next several months (or years if you really wish to delve deep), read the text books given, learn how to apply the theory from hands on experience, and that is just for starters.
    Q:- why, what for?...it is just a simple question, what is so complicated about it?
    A:- There is a certain amount of prerequisite knowledge required to begin to explain. Without which, and an understanding of said prerequisite knowledge that form the basis for an informed discussion, you shall be for ever asking Qs and going down more and more rabbit holes…and yet still asking the same fundamental question.
    Q:- But…im only asking a simple question.
    A:- if it were that simple, why ask?
    Q:- Because I don’t’ know, and wanna know…
    A:- ok, draw an airplane, build it with whatever materials you can find and fly it…then come back to me, as you say, it is simple question and not complicated.

    Indeed it is. And yet…
    There is seeking knowledge, by asking questions and learning, and building upon a solid foundation of knowledge already learnt.. to progress.
    And there is seeking knowledge, by asking questions, but without any understanding of the basics - yet becoming petulant and often polemic and personal in their replies, because they fail to take the time to learn the basics before asking questions that are more nuanced than a simple Google search which failed to provide them their answer, and they get frustrated why it is not a simple one liner!

    Knowledge is everything; but if everything were so simple and not 'complicated'…we’d all be brain surgeons and rocket scientists at the mere click of a button.
    Knowledge takes time to learn …
     
  9. zstine
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    zstine Junior Member

    Quite the insinuation about someone you don't know anything about. If my questions, like "Where did the 1.8 tonne come from?" is so dimwitted, then show me how you calculated it, because I'm confident it is not possible based on the SOR I provided. You guys talk a big talk. Now show me if you can walk the walk.
     
  10. Ad Hoc
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    Ad Hoc Naval Architect

    The replies tell me all i need to know from a technical basis.

    Have you read any of the text JEH provided?

    If not, payload, as a rule of thumb, is circa 20% of full load displacement.

    Sorry, this is not a bar with barflies standing around waiting for their 5min of fame from a heckler.
    Unless of course that's all you want.. just one liner replies in a lame attempt to crack a joke or feel superior? ...in which case.. you'll go nowhere fast, and elicit replies from like mind only.
     
  11. zstine
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    zstine Junior Member

    So you applied a "rule of thumb" based on SWATH boats to a HYSAWS configuration without knowing the design details and then when I questioned where this number comes from, you say I don't know the basics! It is you who are heckling me with these aircraft analogies (fyi I have designed and built aircraft) and I have a fairly extensive understanding of "the basics". Further, your statement that the payload based on 20% displacement is not adequate, "can't see that happening", equate to saying that you don't think a 20,000 lb displacement HYSWAS would be a success, since you based that on displacement alone.. tisk, tisk. Let me inform you that Quest was only 24,000 and very successful HYSWAS. Hard to believe 24,000 lbs is good to go, but 20,000 lbs is not possible. Care to explain why that 4,000lbs turns the design from success to failure??
     
  12. Ad Hoc
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    Ad Hoc Naval Architect

    So, if you know all the answers, why are you asking questions?

    As for the rest, QED!
     
  13. BMcF
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    BMcF Senior Member

    Quest was purely a small-scale technology demonstrator. As such it had very limited space and payload capability. The HYWAS demonstrator was a sub-scale model for some fairly large naval hybrid HYSWAS concepts that were proposed/developed at David Taylor Research Center, by John Meyers engineering group, to bridge a gap between the capabilities of pure hydrofoils and SWATHs, all of which were also being investigated back in those days. At the same time, my company designed a built a different sort of foil-assisted hybrid craft* of similar size and displacement as Quest. Since we all knew each other well (the world of AMVs is s small one), we exchanged a lot of ideas and even some demo rides.

    * Our demonstrator was built as a 1/-4 scale model of a proposed 54-meter 50-knot vessel. It was essentially an ama-stabilized (off foil) super slender monohull (on foil).

    Neither of the above, nor many other test craft we've helped to build and test, had any significant payload or even practical use. Not to mention they were very expensive to build and test.
     
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  14. zstine
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    zstine Junior Member

    Hi BMcF. Thanks for you reply! One question that I can't get out of my head is that Quest, I believe, was 27ft long and at 12T seems to be quite heavy, even with it's appendages. If hypothetically, you could build it lighter (composite materials maybe?) and reduce the weight by a few thousand pounds, keeping everything else the same since you are just going to put that weight back in as cargo, it could then have viable payload. What is the technical issue with doing that?
     

  15. TANSL
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    TANSL Senior Member

    It does not occur to me that there could be any problem and in any case there would be no problem that could not be solved. Maybe check all the stability criteria for the unloaded ship.
     
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