Froude and planing

Discussion in 'Hydrodynamics and Aerodynamics' started by sandhammaren05, Feb 26, 2017.

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  1. sandhammaren05
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    sandhammaren05 Senior Member

    Here's another from Iran
    https://www.researchgate.net/public...mic_forces_on_a_planing_hull_in_steady_motion

    They also try their hand at prop theory. An Iranian friend/engineer explained to me that they have interest in high speed small craft based on history, of small Persian boats outmaneuvering larger Greek ships in battle. They have hopes of beating or competing with the U.S. Navy in the Persian Gulf using small high speed craft. That's only hearsay.
     
  2. sandhammaren05
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    sandhammaren05 Senior Member


    GT15: P=15 shp, w=420 lb
    Compare with APBA DP Class kilo record, V bottom with 55 shp, w=800 lb, U=54 mph.
    My predicted GT15 speed is U=43 mph.

    GT30: P=30 shp, w=550 lb. Compare again with DP Class.
    My predicted GT30 speed is U=50 mph.

    The scaling is a 1/3 power law.

    I predict that the windpower provided to the 150 lb windsurfer running 50 mph is about 30 hp.
    In the run-what was the wind strength (Beaufort scale)? Was it a 2-way avg. or only one direction?
    Outboard speed records are based on a 20-way average.
     
  3. gonzo
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    gonzo Senior Member

    Are you claiming she's not planing?
    upload_2018-4-13_10-42-52.png
     
  4. sandhammaren05
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    sandhammaren05 Senior Member

    Are you claiming that the air flow past the boat is compressible? Is that your prediction or that
    of your so-called physicist colleagues? Explain, please.
     
  5. gonzo
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    gonzo Senior Member

    Certainly. My truck tires have compressed air in them at zero speed.

    Also, could you justify that Baby Bootlegger is not planing due to her pointy stern?
     
  6. sandhammaren05
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    sandhammaren05 Senior Member

    Your truck tires? The discussion is about air flow. Maybe you should ask your so-called physicist friends to explain incompressibility of a gas flowing at
    speeds below sound speed.

    Where's the picture of the boat bottom-!?
     
  7. sandhammaren05
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    sandhammaren05 Senior Member

    Looks like a squared transom to me. What does it look like to you-? telefoon-5071.jpg
     
  8. Barry
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    Barry Senior Member

    Are you serious. Air is incompressible???????????? Maybe as a physicist you should review the Ideal Gas law.
     
  9. Joakim
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    Joakim Senior Member

    Yes air can be taken modeled with incompressible models in fluid dynamics, if the maximum velocity is well below speed of sound (e.g. less than 30%). That doesn't mean that air is incompressible or even that density would be constant. Some details here: Incompressible flow - Wikipedia https://en.wikipedia.org/wiki/Incompressible_flow
     
  10. Joakim
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    Joakim Senior Member

    Peaky likes this.
  11. sandhammaren05
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    sandhammaren05 Senior Member

    You are very presumptious and uncareful. Gas flow past a surface is incompressible so long as the speed is much less than sound speed, and the temperature is well above the liquification point.
     
  12. Joakim
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    Joakim Senior Member

    This is getting funny (or got already more than a year ago)!

    Pointy sterns cannot provide lift, yet a windsurfer can reach 50 knots with a pointy stern. How about a flat bottom hull (or V if you like) with normal square transom (viewed from above) and then you make the transom first a little bit triangular and then more and more. At which angle will the stern become pointy and loose all lift?

    Have you ever discussed face to face about your theories someone who really knows aerodynamics. Or maybe you can present your theory to Savitsky?
     
  13. sandhammaren05
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    sandhammaren05 Senior Member

    If you want to arrive at lift you need the Kutta condition. Using averaged NS eqns. with eddy viscosity is a long way from there. Bad starting place. Are you aware that those eqns. are not valid in the free stream. The free stream, not the turbulent boundary layer, is where the lift appears. Maybe you're confused by a smattering of knowledge about some terms in hydrodynamics.
     
    Last edited: Apr 14, 2018
  14. sandhammaren05
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    sandhammaren05 Senior Member

    What windsurfer-?

    A V-bottom with a very steep deadrise would be a poor design, performance-wise. I wouldn't try to plan sitting on a sailboat centerboard.

    If Savitsky or others want to know what I'm doing then they're free to visit me. As long s I'm not on the water. I'm not a traveling salesman.
     

  15. gonzo
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    gonzo Senior Member

    I think that Hunt's designs with v-bottom steep deadrise have been proven to be very good. In fact, they are still driving powerboat design.
     
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