Sea Sled Design....Bay Sled

Discussion in 'Boat Design' started by kenfyoozed, Feb 18, 2021.

  1. DogCavalry
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    DogCavalry I aim to misbehave.

    Unfortunately I don't know that anyone did proper quantitative analysis, Ken. The pros and cons would be slight, with such a small V. That would require testing with otherwise identical hulls, or some CFD analysis with software capable of modelling the massively turbulent piled up interacting bow waves.
    So: A small loss of lift, and therefore loss of speed and cushioning. A slightly higher focus of air and foam right at the apex of the V, making things a little harder for a single engine. Slightly higher directional stability, from the flow in the tunnel when the hull is yawed.
    Different porpoising characteristics, because the stagnation lines near the transom would be more fore-and-aft, reducing porpoising, and the reduced lift in the tunnel requiring slightly higher hull planing angle, increasing porpoising.

    How it would all work out in practice? I'd be surprised if anyone could put numbers to it. My sense of it is that you would be better served with a straight line transom.

    John
     
    Last edited: Feb 22, 2021
  2. Mr Efficiency
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    Mr Efficiency Senior Member

    It might concentrate aerated water at the centreline, a little more. But that is a guess.
     
  3. BlueBell
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    BlueBell "Whatever..."

  4. Mr Efficiency
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    Mr Efficiency Senior Member

    Love the teeth ! Interesting that he ends up with a boat that is effectively a tri-hull, not dissimilar to the cathedral hulls. The way those hulls originated back in the 50's or 60's, was they morphed from sleds.
     
  5. BlueBell
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    BlueBell "Whatever..."

    Here's another with "good" cavitation:
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    Well, I am thinking that has to be taken "on trust", being a military vessel and all, I'd be surprised if that is the full story, or even the true story. Leaving aside the cavitation business, are we to assume the slanted connection between the "torpedoes" and the hull acts as some combination of buoyant and dynamic lift to keep it on an even keel ? How is pitch stability maintained ?
     
  7. BlueBell
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    BlueBell "Whatever..."

    KennyF,

    The pro's to a flat hull at the transom would be: easier to get on plane (lower planing speed), potentially faster hull, better fuel mileage, less wetted area (but not much less), closer to the Hickman design you've fallen for, less central aeration perhaps, greater lift (accommodating higher payloads).

    The con's, higher drag in displacement mode (not applicable I suspect), I'm sure someone will point out more but that's all I can think of.

    FYI
    DogCalvary's hull is flat for more that a foot forward of the transom.
    Then his rate of climb is very shallow forward of that, increasing appreciably by midship.

    Thoughts?
     
  8. kenfyoozed
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    kenfyoozed Junior Member

    Thats the way I will probably keep it as designed.
     
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  9. BlueBell
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    BlueBell "Whatever..."

    Perhaps you got my meaning backwards.
    You haven't drawn it flat.
    Are you saying you're going to keep as shown?
     
  10. DogCavalry
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    DogCavalry I aim to misbehave.

    If you keep the slight V Ken, please document what you find in operation. It is, as the 6 fingered man said, for science.
     
  11. kenfyoozed
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    kenfyoozed Junior Member

    I ant decided which way to go. The designs i am working off of show a slight v at the transom but the station forward is more flat. So it goes from inverted v to almost flat then to shallow inverted V. Im moving very slow on this trying to do the best I can in the design stage. I am sure i am missing something.
     

  12. DogCavalry
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    DogCavalry I aim to misbehave.

    Whatever you do or don't do, make sure that the apex of your tunnel is a straight line, from about mid length, all the way to transom.
     
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