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How do I reduce the coeff. of friction against water?

  1. Nov 27, 2007 #1
    hello,

    i need to coat the bottom of a plastic model boat that will be moving against water with something that will reduce the coefficient of friction. Any ideas? Thanks in advance.

    p.s. household items would be best, I need it by tomorrow
     
  2. jcsd
  3. Nov 27, 2007 #2
    would something like petroleum jelly work? or would i be better off with something like wax?
     
  4. Nov 28, 2007 #3
    what ever you put it should be a very thin layer so that it will smooth out the bottom and not add much more friction it's self
     
  5. Nov 28, 2007 #4
    I've heard it claimed that a very rough surface will actually work (something about making the flow more laminar?), no idea whether it's true but it sounds interesting to test.
     
  6. Nov 28, 2007 #5
    all i know is that in cars(drag racing) they like to put the least amount of paint
    yes some paint is needed to look good but also with out paint the surface is not smooth creating more drag

    so if any of that helps you
     
  7. Nov 28, 2007 #6
    thanks guys, the tests went well today, even though i went without anything on the bottom of the boat. Appreciate the thoughts.
     
  8. Nov 28, 2007 #7

    Astronuc

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    Staff: Mentor

    Basically one wants to reduce drag by shear with the water, as opposed to drag due to the cross-section projected into the on-coming water.

    Teflon or silicone would probably work the best to reduce the adhesion of the water, but teflon coating is not something that can be done overnight. Silicone sprays would wash off eventually. There are certain silicone paints or coating compounds which are hydrophobic.
     
  9. Nov 28, 2007 #8
    In the car paint industry, and possibly others, it is referred to as "wetting" you want to maximize the wetting of your body against water. There are a number of paints that specialize in reducing hull friction to the "wetted" surface by increasing (yeah, i know it sounds counter intuitive) the cohesion of water to the bonded surface. The upshot is that instead of a solid to water boundary layer what happens is one adds the mass of a small laminar water layer to the mass of the hull, but boundary effects are minimized by limiting the friction to a water to water boundary layer.

    Actually competition boats, America Cup etc. spend enourmous amounts of money on just such surfactant research. (Not a guess, I spent 7 years as a systems engineer for a leading global paint manufacturer.)
     
  10. Nov 29, 2007 #9
    Try some paints that are hydrophobic. It's like the duck feather.
     
  11. Nov 29, 2007 #10
    so wetting is the same thing i was saying
     
  12. Nov 29, 2007 #11
    No, actually that is the opposite of what you, the OP, Astronuc and Pixel were saying.
     
  13. Nov 29, 2007 #12

    Danger

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    Gold Member

    My solution would be to glue your model to a dolphin, but I suppose that there's something in the rules of engagement that would rule that out.
     
  14. Nov 30, 2007 #13
    Perhaps Danger, but perhaps you could find a loophole by employing one of those out of work dolphins that were trained to lay mines on ships hulls?

    Wetting is the chemical effect of lowering it's surface tension letting the material slide rather than creating a "repellent" coating that raises the surface tension. An example of the latter is the coating put on windshields that raises the surface tension sufficiently that the bead of water has an incidence of over 72 degrees and thereby can no longer "stick" to your windshield, but rolls off. The wetting would produce exactly the opposite effect. While this would lower the resistance of the windshield to more water flowing over it, it would spell utter disaster for the poor soul trying to drive in the rain. Good for boat hulls and sliding electrical contacts. Bad for windshields.
     
  15. Dec 1, 2007 #14

    dst

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    I know it's over but soap? Is that cheating? :D
     
  16. Dec 1, 2007 #15

    Danger

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    Gold Member

    They only want you to think that they're out of work... :uhh:
     
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