How small can a towing tank be?

Discussion in 'Hydrodynamics and Aerodynamics' started by Todd Miller, Mar 17, 2014.

  1. Ike
    Joined: Apr 2006
    Posts: 2,576
    Likes: 408, Points: 83, Legacy Rep: 1669
    Location: Washington

    Ike Senior Member

    Todd that is a great idea. I suggest you contact the Northwest School Of Boatbuilding in Port Hadlock. I would bet they would be really helpful and might even send some of their students over to help you out. Next time I go to Port Townsend, if I get the chance, I may stop by and see how it's coming on. Even a small tank and model is really a great way to demonstrate Archimedes Principle and the basics of buoyancy and stability.
     
    1 person likes this.
  2. Manfred.pech
    Joined: Apr 2010
    Posts: 602
    Likes: 82, Points: 28, Legacy Rep: 319
    Location: EU

    Manfred.pech Senior Member

    Did you ever hear of the Prandtl (Prof. of Aero- and Hydrodynamics) Test Tank ? http://www.dlr.de/en/desktopdefault...d-26563/gallery-1/gallery_read-Image.1.17454/

    http://www.dlr.de/schoollab/desktopdefault.aspx/tabid-4964/14529_read-13948/ and http://www.dlr.de/schoollab/Portaldata/24/Resources/dokumente/hb/prandtl-kanal.pdf
    http://www.google.de/imgres?imgurl=...0sU6HVAcrrswaG8oDYBg&ved=0CEQQ9QEwBA&dur=1443

    [​IMG]

    [​IMG]
     
  3. Richard Woods
    Joined: Jun 2006
    Posts: 2,209
    Likes: 171, Points: 63, Legacy Rep: 1244
    Location: Back full time in the UK

    Richard Woods Woods Designs

    I went to see Todd a couple of days ago and now have a better understanding of what he would like to do, and what he can do. We discussed a number of different ideas, not just boat related

    The Prandtl test tank seems a great idea that would suit his school and students

    Richard Woods
     
  4. Petros
    Joined: Oct 2007
    Posts: 2,936
    Likes: 148, Points: 63, Legacy Rep: 1593
    Location: Arlington, WA-USA

    Petros Senior Member

    that is a great way to do it. Simple design and easy to build. But I would dump the paddle wheel, instead put a propeller in the underside, in the return duct, driven by a shaft that is powered by an electric motor (that is outside the tank). You can get a fairly inexpensive plastic prop designed for electric trolling motors at any marine supply store. with that set up you get less turbulence and less work, and you can hold a steady state flow and do comparisons between hull designs. that can be made fairly large without too much cost.
     
  5. BMcF
    Joined: Mar 2007
    Posts: 1,065
    Likes: 83, Points: 48, Legacy Rep: 361
    Location: Maryland

    BMcF Senior Member

    :p......
     
  6. Manfred.pech
    Joined: Apr 2010
    Posts: 602
    Likes: 82, Points: 28, Legacy Rep: 319
    Location: EU

    Manfred.pech Senior Member

    Yes, of course. One can make it better, bigger, longer, wider with instruments, a magic stick inserted in the model combined with a computer and filters to avoid turbulences. The Prandtl water channel is something like a minimum. Built more than 100 Years ago (1904) it helped to develop the theories of turbulent fluids and boudary layer. And the idea, to have a small test channel in the cellar/basement in my house to test models of hulls or profiles seems to be very attractive to me.

    [​IMG]
     
    1 person likes this.
  7. Todd Miller
    Joined: Mar 2014
    Posts: 3
    Likes: 0, Points: 1, Legacy Rep: 10
    Location: Quilcene WA

    Todd Miller New Member

    Thanks for the ideas. I really like the idea of the Prandtl tank, I had actually been thinking of how an "Endless Swim" lap pool works and this is nearly the same idea. I teach science and woods and I could imagine using it at all levels to just show the basics. As Uli suggested using milk to show flow could add to it. My kids build water rockets when we study Newtons laws and many of them have a very Aristotlian view of turbulence, they think it turns around an object and "pushes" it.

    Richard Woods helped me clarify my thinking too. And this is something I can have some of my less motivated shop students build for me since they can't seem to find projects of their own to build

    Todd
     
  8. Manfred.pech
    Joined: Apr 2010
    Posts: 602
    Likes: 82, Points: 28, Legacy Rep: 319
    Location: EU

    Manfred.pech Senior Member

    Great! Will you test hulls for your clients, making scientific research for the students you are giving lectures at University, try to get answers for yourself? Would be nice to be your neighbour and discuss the results with you.

    And a last question: Do you plan to make windows with glass at the bottom and the sides to watch the flow, the whorls the vortices and eddies and the flow around the hulls making them visible in the water by mixing chemicals (or sesame/linseed) into the flow and filming them with a camera running with the hull?
     
  9. Ad Hoc
    Joined: Oct 2008
    Posts: 7,283
    Likes: 1,171, Points: 113, Legacy Rep: 2488
    Location: Japan

    Ad Hoc Naval Architect

    All the above :)

    No. Too many earthquakes on a regular basis, so everything is "simply supported" as such and not 100% fixed; to allow movement during a quake. As such I've compromised to save cost and construction, i.e. to minimise all possible sources of leaks during a quake!
     

  10. froudedude
    Joined: Feb 2010
    Posts: 10
    Likes: 1, Points: 0, Legacy Rep: 10
    Location: Annapolis

    froudedude Junior Member

    Model size is the real driver with a tow tank. You have to avoid shallow water effects (based of depth Froude number) and blockage effects (base on model depth Froude number and tank cross sectional area). Remember that errors scale to the cube of the scale factor .

    Also laminar flow is a huge problem with models under 5 ft LOA and moving at less than about 3 feet per second even with turbulent stimulation
     
    Manfred.pech likes this.
Loading...
Similar Threads
  1. mtumut
    Replies:
    4
    Views:
    1,890
  2. Barry
    Replies:
    5
    Views:
    1,917
  3. laukejas
    Replies:
    40
    Views:
    6,469
  4. DCockey
    Replies:
    0
    Views:
    1,764
  5. Rurudyne
    Replies:
    10
    Views:
    2,644
  6. seanGT
    Replies:
    12
    Views:
    3,894
  7. Surfer Naval Architect
    Replies:
    6
    Views:
    2,446
  8. mtumut
    Replies:
    17
    Views:
    2,981
  9. mtumut
    Replies:
    8
    Views:
    3,115
  10. cmckesson
    Replies:
    0
    Views:
    1,315
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.