Catamaran Hull Squat

Discussion in 'Hydrodynamics and Aerodynamics' started by francotripepi, Feb 28, 2019.

  1. francotripepi
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    francotripepi Junior Member


    I do understand the concept....not necessarily how to put it into practice....if that is a NO, I don’t know....then NO, I don’t know
     
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    This is where your specs meet an insurmountable barrier, that is shallower than is realistically possible with a slender-hulled cat, even if you somehow manage to mount engine(s) successfully between the hulls. Your ultra-shallow running might be achievable with a "flats" boat, a flat bottom, rectangular plan, with a tunnel developing aft that allows water to rise into the prop. That will give you a stable boat, but choppy water will not be agreeable. I suppose if you entertain a jet drive, you can reduce the draft nearer to your mark, with a cat, but 8-10" is very difficult.
     
  3. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    Ok

    So your 24 footer...i don't understand these units so this is roughly 7.30m.

    Let's say, for example this design full load weighs 20 tonne.
    The LD ratio will be 2.7
    If it weighs 15 tonne LD = 3.0
    If it weighs 10 tonne LD = 3.4
    if it weighs 5 tonne LD = 4.3
    if it weighs 1 tonne LD = 7.3
    if it weighs 0.5tonne LD = 9.2

    Your requirements suggest you are looking for a hull design with an LD ratio of at least 7 as a minimum.

    In other words, you need your design full load, that is structure fuel engines passengers etc etc, everything...to weigh a maximum all up of 1.00 tonne.

    Is that possible?
     
  4. francotripepi
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    francotripepi Junior Member


    1 ton equals roughly to 2000 pounds, that seems light, but close enough....perhaps a more realistic would be around 1.5 tons

    Is it realistic? I don’t know....but realistic and achievable are two different things
     
  5. francotripepi
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    francotripepi Junior Member

    Probably, that is why I left open other ways, as in planning or semiplanning
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    You might get a dead-flat (at the transom) fat-hulled planing cat with jet drives to run in a foot of water, but the life span of the drives would be limited chewing sand on more than an occasional basis, and the fuel bill with twin jets might hurt the pocket. Jet outboards might be considered.
     
  7. philSweet
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    philSweet Senior Member

    Deck boats have some fall to them so that the bridge deck clearance is acceptable in the bow, and materials usage is minimized in the stern. The slope is not normally a bother to people. The motor sits at the right height and is easy to access from the boat. And the deck drains. If you ship a wave onto the deck, you don't want to stuff the boat. You want the water to move aft and drain quickly. For shallow draft and trailerablity, you should look at a monohull deckboat in the sizes under consideration. Cats really are a nuisance in this size range, they just don't have enough beam to get the job done. And they don't get any better fuel economy because they are as heavy or heavier than an equivalent mono and there is too much drag in the tunnel. The inflow to the prop is challenged and the maneuverability at speed is usually less.

    So there isn't anything that wants to be fixed in the cats you pictured, but I think a design similar to the Hurricane type deck boats would be better suited to your wants and area of use. I lived on Key Largo for ten years. BTW, a 15 to 18 knot speed is stepping out pretty well. That would be a bit of a problem for many of the cats you pictured. The displacement ones wouldn't go that fast, and the planing cats would mostly be just on the edge of planing, nose high, and not very efficient at that speed.

    SD 2400 OB | SunDeck https://www.hurricaneboats.com/sundeck/sd-2400-ob
     
  8. JamesG123
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    JamesG123 Senior Member

    He was suggesting something like this:

    [​IMG]

    Ie; he was kidding.
    But in truth, the solution to your "problem" is length.
     
  9. francotripepi
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    francotripepi Junior Member


    James!! That’s exactly what I need!! Who makes that beauty? Look at that....emmm....sheer
     
  10. francotripepi
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    francotripepi Junior Member


    Phil you are right, I meant mph instead of knots....btw, that means you know the waters I’m talking about, and that those flats are everywhere....and stunning too, on the Gulf side and up by the Everglades.....you know most boats can’t go there, not even idling
     
  11. Mr Efficiency
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    Mr Efficiency Senior Member

    A catamaran having a small waterplane area, is about the worst choice to negotiate extreme shallows. The best, for that, would be a lightweight, flat-bottomed boat, with the tunnel right aft that allow water to rise into the prop. You can't have everything, though, and you will get hammered in a chop.
     
  12. fallguy
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    fallguy Senior Member

    What is the depth of the areas you are talking about?

    You can realistically only use a planing hull.

    What is the minimum draft of a 24' cat?

    If AH is here; all I can offer is a few questions to help the dialogue along.

    Not to mention, I'd like to know if my boat can get to these places witj a 24" draft.
     
  13. Mr Efficiency
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    Mr Efficiency Senior Member

    He wants 8-10 inches ! Probably not impossible, but not gonna happen with a cat, you would have to say.
     
  14. francotripepi
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    francotripepi Junior Member


    Fallguy, with 24” it’ll be close to impossible to get there....and those areas are extensive, full of wildlife, plain spectacular....but you need shallow draft
     

  15. Ad Hoc
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    Ad Hoc Naval Architect

    Can you define what is considered to be the maximum draft possible for this location then.
     
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