charts/rules of thumb for efficiency of different hulls (mono/cat/disp vs plane)

Discussion in 'Hydrodynamics and Aerodynamics' started by big_dreamin, Oct 20, 2016.

  1. big_dreamin
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    big_dreamin Junior Member

    Okay, great, so everyone hates the original chart, could someone post a BETTER one then, or reference some texts that get a little closer to the mark?

    I'm aware there are lots of variables but this is not an insurmountable problem. There are many "catamarans" that have crappy hull shapes that almost shouldn't count as a catamaran, low bridgedecks and transoms hanging up in waves for instance, but at the end of the day you can at least compare optimal shapes to other optimal shapes. It's just like when I was studying aircraft foils, there was NACA research that showed a number of different foils giving comparisons of lift, drag, usable speeds (ie some were more efficient up to a given speed where it lost laminar flow) and similar. There's GOT to be some similar text for marine use.
     
  2. TANSL
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    TANSL Senior Member

    Yes, you are right, for marine use can be set exactly the same comparisons with NACA profiles.
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    A better comparison basis would have been simple speed Vs resistance, for those various generic hullforms, of similar length and weight. At crawl speed, the displacement monohull would have registered the least resistance, because it has less wetted area than the displacement cat, and is not hampered by submerged transom drag of the planing hulls. At "hump" speeds, the displacement cat would be a clear winner because of less wave-making resistance than the rest, but at speeds of say, over 25 knots, the planing hulls would come into their own, through their ability to reduce both wetted area and wave-making drag, because dynamic lift has raised the boat partially out of the water. The planing cat would tend to lag behind the planing monohull, but with increasing speeds it can benefit from aerodynamic lift more than a mono. The displacement cat is suffering from wetted drag at higher speeds,because it maintains much the same immersion as speed increases.
     
  4. big_dreamin
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    big_dreamin Junior Member

    Sounds great, any idea where I can find such charts in detail now? :) Even if it's in some engineering text.
     

  5. Mr Efficiency
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    Mr Efficiency Senior Member

    I've seen such charts, but they more usually compare displacement, semi displacement, and planing monohulls, rather than include cats.
     
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