Simplified Froude-Krylov Force

Discussion in 'Hydrodynamics and Aerodynamics' started by CarlosK2, May 11, 2026.

  1. CarlosK2
    Joined: Jun 2023
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    Location: Vigo, Spain

    CarlosK2 Senior Member

    Screenshot_2026-05-12-09-54-03-96.jpg

    Thomas Harrison Butler in Memoriam

    Obviously, if the 1 Ton WindSurf Board is sailing with a gennaker at 17 knots, surfing a wave that's traveling at 20 knots is no mystery

    But It's more reassuring to know that the Surfboard will surf well even without great speed, pushed at the beginning by the Froude-Krylov force and propelled by the Almighty Force of the Earth
     
  2. CarlosK2
    Joined: Jun 2023
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    Location: Vigo, Spain

    CarlosK2 Senior Member



    A boat bought second-hand for 4 K Euros surfed big waves (which are not the ones shown in the images) at 14-20 knots, controlled by a clumsy pilot with little brainpower.

    What's the point of spending a fortune on a sports yacht only to spend another fortune on an expensive autopilot and not even reach the heights of the classic solutions of those who came before us

    A MiniTransat for an old fogey is a practical matter of comfort and safety, and of respect for tradition and things done well with care
     
  3. CarlosK2
    Joined: Jun 2023
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    Location: Vigo, Spain

    CarlosK2 Senior Member

    Pogo 2: 6.5 m, 1000 kg
    Pegaso SLK-599: 5.99 m, 800 kg

    1000 kg = 800 kg (6.5/5.99)^3

    Less is more

    with 30 knots of wind, both sail at 17 knots downwind; but the A5 gennaker is much smaller and more comfortable on a rotating bowsprit

    Of course the old sailor has to get up from his seat, a cruelty of the designer
     
  4. CarlosK2
    Joined: Jun 2023
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    Location: Vigo, Spain

    CarlosK2 Senior Member

  5. Robert Biegler
    Joined: Jun 2017
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    Location: Trondheim

    Robert Biegler Senior Member

    What does the hull shape look like? To get the centre of buoyancy aft of the centre of floatation, the waterplane aft of the centre of floatation needs a higher water plane loading, or greater average draft, than the part of the waterplane forward of the centre of floatation. The ways I know to achieve that would be lots of rocker in the run, a bustle, or an immersed transom. What is your choice?
     
    Last edited: May 19, 2026 at 3:28 PM
  6. tropostudio
    Joined: Dec 2014
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    Location: St. Paul, MN, USA

    tropostudio Senior Member

    Center of Flotation is the centroid of the waterplane area. CF could be ahead of or behind the CG at rest or in motion.
    If I'm correct, Carlos2K is using it as a factor in a boat's ability to surf or at least tend toward bow-up on a stern wave.
     

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