Foil for current-driven propulsion?

Discussion in 'Hydrodynamics and Aerodynamics' started by MacktheYounger, Aug 30, 2022.

  1. patzefran
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    patzefran patzefran

    sorry,
    E²=m0²*c^4+c²*p²
     
  2. gonzo
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    gonzo Senior Member

    Everything in this thread is about Newtonian physics. Light or near light speeds behavior is irrelevant.
     
  3. gonzo
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    gonzo Senior Member

    It depends on whether they have a relative velocity or not.
     
  4. gonzo
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    gonzo Senior Member

    You are missing the definition of potential. It is equal to the amount of work done to get an object into its position.
     
  5. patzefran
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    patzefran patzefran

    If you make the velocity of the particle negligible relating to c, you will find the classical limit of energy
    E=m0*c²+p²/2m wich depends again of the observation frame !
     
  6. patzefran
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    patzefran patzefran

    By no way we have to deal with potential theory to compute the performance of a sailboat, this has nothing to do there.
     
  7. patzefran
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    patzefran patzefran

    Agree !
    forces depends only on relative position and velocity of objects, so they are independant of the Galilean reference frame we use ( fixed to land or to water )
    which confirm my results !
     
  8. dustman
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    dustman Senior Member

    So if you can sail up a river with no wind against the current, what's to keep you from sailing in the ocean with no wind by simply getting your foiler going with a motor? Or does sailing against the apparent wind and current somehow make this whole thing work?
     
  9. Doug Halsey
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    Doug Halsey Senior Member

    The river keeps going, but your motor doesn't.
     
  10. dustman
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    dustman Senior Member

    How do you get around the fact that you are creating your own wind by the motion of the boat so you will always be heading directly into the wind? If you put the sail to one side or the other you would only create sideways and backwards lift components. How exactly is the energy of the river current transformed into upriver motion, what are the forces acting on the sail and keel once you have stabilized your course upriver? I also imagine that this would require tacking upriver?
     
  11. Doug Halsey
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    Doug Halsey Senior Member

    The river is creating the wind. If you are aimed directly up the river the wind that you feel will be coming from directly behind you.
     
  12. dustman
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    dustman Senior Member

    How would you make progress upriver?
     
  13. Doug Halsey
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    Doug Halsey Senior Member

    The wind coming from behind you allows you to sail just like sailing downwind in the ocean. To make progress up the river you have to head up and increase speed enough to have a positive VMG - something that many (but not all) boats are capable of doing.
     
  14. Doug Halsey
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    Doug Halsey Senior Member

    Many is probably an exaggeration. AC50's and other fast foilers can certainly do it. Not too many others can.
     

  15. gonzo
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    gonzo Senior Member

    That is incorrect. Wind is created by a difference in potential.
     
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