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B Calculate pressure on surface moving in water

  1. Oct 3, 2016 #1
    Hello bright minds,

    I have a practical problem for which I need help solving, and I'm sure someone could help.

    I am wanting to place a pick up (sort of a backwards facing venturi type structure) under my kayak to fill up and supply a box with fresh water for my live baits. I would like to know how one would calculate the required velocities of the kayak (if possible, including friction in pipes) to be able to overcome the head height (about 20cm max) to fill my box. Please see my simple diagram for a visual description of what I am trying to do.

    Attached Files:

  2. jcsd
  3. Oct 3, 2016 #2


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    hi brentch

    welcome to PF :smile:

    cant help you with your specific problem, hopefully some one can. but just as a guide for future posts
    It's better to post an image directly, rather than making people have to open another document :smile:


  4. Oct 3, 2016 #3
    Thanks for the help Dave!

    I'll post the pics directly next time.
  5. Oct 5, 2016 #4
    Bernoulli's principle

    but it has no consideration towards effects like viscosity, friction in pipes

    i think , u can considerably lessen the severity if these effects by
    making the tube less steep, as shown by thick black line(pointed by red arrow)

    this will lead the incoming liquid to the container without much Deterrence(and water flow will be less chaotic)
    so now use this equation , with following considerations- pressure at head end is Patm, pressure at the tail end is ρv2**,velocity at the tail(other end of the tube- thick black line) to be v (velocity of the boat), h as height of the head from the water level around the kayak (asuming elevation at the tail end to be zero)
  6. Oct 5, 2016 #5
  7. Oct 5, 2016 #6
  8. Oct 6, 2016 #7
    Could you view the image ?
  9. Oct 7, 2016 #8
    Hey Shreyas, apologies for the very late reply. Unfortunately I am unable to view the image...
  10. Oct 7, 2016 #9


    Staff: Mentor

    This sounds like a case better suited to experiment because of complications like friction and viscosity.

    Strap a tube with the proposed length and angle to the side of your kayak and try it out. You can see visually how much flow comes out the high end of the tube.
  11. Oct 7, 2016 #10
  12. Oct 7, 2016 #11
  13. Oct 7, 2016 #12
    I am wanting reply for the above post
  14. Oct 7, 2016 #13
    See this
  15. Oct 8, 2016 #14
    Aha! I can view it now, thank you so much for the effort of using and solving the equation. I will play with it this weekend and see what I come up with. And to Anorlunda, yes, I will also get to try out the pipe strapped to the side of the boat this week!

    Thanks for all the help, clever people! I'll post some photo's of the unit if I manage to get it to work.

    Have a great weekend.
  16. Oct 8, 2016 #15
    That's great
  17. Oct 8, 2016 #16
    anyone PF member -
    is it that I have missed something while getting the pressure
    "finding pressure at the tail end"
  18. Oct 8, 2016 #17
    Very eager to see your manoeuvre
  19. Oct 13, 2016 #18
    What happened ??
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