What hull will be most efficient between 8-12 kts?

Discussion in 'Hydrodynamics and Aerodynamics' started by dustman, Oct 9, 2021.

  1. fallguy
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    fallguy Senior Member

    I like the double 9.9 better versus a single 25
     
  2. dustman
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    dustman Senior Member

    Where is this high load going to come from? Loads should always be pretty widely distributed, I can't really see a scenario where it wouldn't be.
    Awesome, I'll invite you for the launch! If you're willing to set set foot on my deathtrap that is o_O
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    Was I correct in saying the frame of these hulls are not attached directly to the skin, but there is intervening PU foam ? That seems very likely to lead to crushing.
     
  4. dustman
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    dustman Senior Member

  5. dustman
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    dustman Senior Member

    There it is, didn't want to post a drawing because this will likely not be the finished product, and on these forums drawings are forever, and you can never live them down.
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    OK, I am getting a rough idea, these hulls are actually round tubes ?
     
  7. dustman
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    dustman Senior Member

    That's what I'd like to do, but not sure that'll give me enough reserve buoyancy. The waterline would be 2-3" below the center of the tube. I figure during a beam on breaking wave the water would mostly go over and under and minimize energy transfer to the hulls. And seems like it would sideslip pretty well.
     
  8. Mr Efficiency
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    Mr Efficiency Senior Member

  9. dustman
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    dustman Senior Member

    No sir, I want it to cut through the water with grace. I've been on a few pontoon boats, not good. And this will be lighter and without the problem of trying to attach them, and pontoons can leak and get holes in them.
     
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    What makes you think your boat is different to such a
    'log' pontoon boat ? GRP will not be lighter than alloy either, if it is, the whole construction is suspect
     
    Barry likes this.
  11. dustman
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    dustman Senior Member

    The form is not all that different, except the transition, which will make quite a bit of difference in resistance I suspect.

    200ft2 of 1/8" aluminum is about 350lbs. So aluminum pontoons would weigh at least this much, plus whatever I have to do to adapt them.

    -20'x4" 1/8" aluminum square tubes(x2) 100lbs
    -60ft3 2# foam 120lbs
    -200ft2 6oz fiberglass wetted and coated until smooth, 28lbs(according to a couple sources about .14lbs ft2)
    -3ft2 aluminum plate 10lbs
    -Total 258lbs(probably an additional 20 lbs for various stuff, so let's call it 280lbs)
    -520lbs with 6# foam
     
  12. Mr Efficiency
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    Mr Efficiency Senior Member

    You are talking a flimsy glass skin that is deficient in just about all departments. It just isn't feasible that you could come up with a single skin GRP construction that is markedly lighter than alloy, with the necessary properties. You are relying on this foam as a structural element, and very few people would endorse 2lb foam as structural
     
  13. dustman
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    dustman Senior Member

    I am relying on the tube as the structural element, the foam and fiberglass around it will distribute the load to the tube.

    On side of the tube has 960in2, at 38psi that's 36,000lbs if the load was fully distributed across that area.

    What kind of load are you envisioning that could cause this system to fail?
     
  14. dustman
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    dustman Senior Member

    The skin is mainly there to keep water from saturating the foam over time, to resist abrasion, minor impacts, and to achieve a smooth surface.

    I forgot to add weight for hull paint in my analysis.
     

  15. Mr Efficiency
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    Mr Efficiency Senior Member

    Hold the phone here, are we talking about a 4" square alloy tube with 1/8'" wall thickness being the longitudinal strength member ? And similar providing the athwartship strength ?
     
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