# can Superconductivity be used to repel water?

Can water be repeled with the force from superconductivity gathering current on the surface cuased by Faraday law of induction? I'm trying to make a ROV that can run underwater that uses superconducters close to the surface of the outer skin of the ROV to negate a tad of the friction caused by water. Since I'm getting differnet answers can any of you support your position with a article?

• Just reading the title, I totally though this was going to be a pop culture reference to Back to the Future. I was this close to leaving an answer of "Yes, of course, but you have to have enough power". Commented Oct 22, 2011 at 21:08
• Such questions arise from "good counsel", don't they? Commented Oct 23, 2011 at 11:28
• This is for personal interest why? Commented Oct 23, 2011 at 19:22

The way to minimize drag in any fluid is to minimize disturbing it.

Fluids don't have friction the same way solid objects have friction, by a sliding interface.

When fluid flows next to a surface, it sticks to the surface. The "sliding" is actually in the form of viscous deformation of the fluid itself in a layer next to the surface (the boundary layer).

What causes the most drag is turbulence. That's when the boundary layer breaks away from the surface and you get eddies, which suck up energy, i.e. drag.

The best way to minimize drag (in a vehicle not moving too fast) is to keep the boundary layer stuck to the surface (laminar flow).

In aircraft, a technique used to keep the boundary layer attached to the surface is to install vortex generators.

• ok but what about highspeed vehicles, plus what would say the range is for your definition of low speed and high speed? Commented Oct 22, 2011 at 15:18
• @Rudy: Check out Reynolds Number. Commented Oct 22, 2011 at 15:48
• Why wouldn't this reduce friction: en.wikipedia.org/wiki/Supercavitation
– user2963
Commented Oct 26, 2011 at 0:13
• @zephyr: good question. That's a flow regime beyond laminar or turbulent flow, and I'm sure has its own physics, beyond what I studied in fluid mechanics. Commented Oct 26, 2011 at 3:16

You won't negate any of the friction with the water by preventing it touching the skin, you'll just make the friction worse, because the boat will be slightly bigger. The amount of friction force is entirely determined by the momentum transferred from the boat to the water, and this quantity doesnt really care if the water is touching the boat or not. It is entirely determined by the flow required to make the water go around the boat, and the wakes that develop drag the boat the same amount whether it is directly touching, or levitating.

• but wouldn't it reduce drag at higher speeds Commented Oct 22, 2011 at 13:33
• if i used it to make a bulge around it would try following back to the area around the tail but it wont touch the tail Commented Oct 22, 2011 at 13:35
• also i dont excpect to negate all the friction just a reduce like 5% would be good Commented Oct 22, 2011 at 13:37
• @Rudy: The point is that the drag in the water is determined by the turbulent flow in the water, which doesn't care if you push the contact point out, except that there is slightly more surface area. Maybe you can get 5% drag reduction, but then you can get the same reduction by changing the shape of the boat. The surface properties are more or less irrelevant for the drag-flow in the turbulent regime, at high speeds. At very,very low speeds, you will have pure Stokes flow, and then you increase the drag by pushing out for sure. Contact points make no difference, tail or head. Commented Oct 22, 2011 at 13:44

Yes, if you make insanely powerful magnet based on this superconductor. In any way, this won't be enough to go without friction underwater.

And the sad part is that high-temperature superconductors can't withstand strong magnetic field, and loose their superconductivity. Super-strong magnets are helium cooled.

Checkout supercavitation.

• well i just want to reduce it with the coils if i reduced it to much i think it would just sink but if i could reduce it enough like pinpoint superconductors at certain points i may reduce it to improve the effiency of motion in water. Commented Oct 22, 2011 at 2:40