Magnetohydrodyamic Submarine

In the movie, The Hunt for Red October, a renegade Soviet Submarine has a new silent drive propulsion system. They call it Magneto-hydrodynamic propulsion. That sounds like Hollywood technobabble, but it's actually based in reality (mostly). We recreate this type of submarine with some 3D printed parts, batteries and some magnets.

Supplies

Battery Pack

Switch

Some #4 screws and nuts

AA Batteries

Two BY0X08, 2" x 1" x 1/2", neodymium magnets

Some electrical wire

Aluminum/stainless steel plates

3D Printed Parts (STL Files)

Lower shell

Upper Shell

Drive bracket

Step 1: 3D Print Parts

We've included the STL files in the supplies list! Or, design your own!

We designed a bracket that holds two pieces of aluminum on either side of a rectangular passageway. The model also has provisions for positioning two large block magnets above and below the passageway.

We used a two part assembly, where the top snaps onto the bottom. Since the top magnet is in the top half of the hull, this worked nicely to allow the strong attractive force between these powerful magnets to pull the halves together. It didn't require any other method of securing them.

The submarine in the movie had a dual propulsion system. We only have one drive, but we designed two inlets and outlets to give it the dual drive look.

The top and lower shells each took over 12 hours to print on our MakerBot.

Using the bracket drawing as a guide, bend some thin aluminum or stainless steel into the "L" shape as shown.

Step 2: Saltwater Test

Before going any further, we filled a smaller container with water and mixed in a bunch of salt to test how our submarine works.

We assembled the drive bracket, with the aluminum brackets and magnets. With the drive assembly in saltwater, hooked up to a power supply, it really moves some water!

Step 3: Assembly

The assembly is pretty straight forward. Start by fastening the conductive plates to the drive bracket. We used brass nuts to hold the wires in place as well.

Insert the drive bracket assembly into the lower shell, fastening with more brass screws and nuts.

Next, wire in the switch. See the schematic for wiring directions!

We designed the sub in such a way that that the pieces are held together by the attracting magnet. Place one magnet in the top assembly and one in the bottom. This provided enough force to hold the pieces together.

Next, we wrapped the battery pack in many layers of packing tape in an attempt to waterproof it...a Ziplock baggie might be better. The bottom magnet holds the battery pack in place.

Step 4: Final Test

For our final test, we filled an aquarium with about 20 gallons of water and added a lot of salt. For our first test, the salt level was about 3.5%, which is typical of our oceans. It worked!! It was slow going, but the submarine was definitely being propelling by batteries and magnets.

To make the submarine go even faster, we mixed in even more salt. With the salt level near 30%, which is the level of the Dead Sea, the submarine moved faster! Check out the video for the start to finish process.

Step 5: This Is Cool, But How/why Does It Work?

Salty water conducts electricity. Imagine a drive tube with two conductive plates secured on opposite sides of the tube. With one grounded and the other connected to a voltage, a current flows through the water across the gap.

The resistance of the water changes depending on how much salt is dissolved in it. The more salt, the more current you’ll get. Since submarines operate in the ocean, we’ll assume the operating fluid is seawater, roughly 3.5% salt by weight.

Next, we’ll place two magnets sandwiching the tube, top and bottom. Now the water within sees vertical magnetic field.

Finally, let’s consider the Lorentz force. Consider what's happening to a tiny little bit of conductive water within that tube. The right hand rule says that, with a current flowing in one direction, and a magnetic field runs in a direction perpendicular to that electric flow, then the bit of water will feel a force that’s perpendicular to both of those directions.

Whew, that’s a mouthful. Let’s express that graphically with the right-hand rule. If the current runs in the direction of the thumb, and the magnetic field with the index finger, the force is down the middle finger.

Science for the win!!!

Comments

[rhodeskid]

This is excellent! Well done presentation. Do you happen to know what would happen if one of the magnets was turned so that the two magnets repulse each other?

[Polymorph]

This would result in no thrust. Water would just rotate in a flattened donut inside the chamber.

[daan V L]

not completely, a really small amount of thrust will actually be created. it just takes a lot more energy to get the same thrust in this case to see why see the 2 rails as wires and see the water as a wire shortcirquiting it. now visualize the magnetic fields, on one side of the short cirquiting wire it will have the same magnetic polarity meaning it will propel(in this case the polarity isn't directly as a magnet but on a smaller scale, visualize the electronspin as a spin orbiting around the wire, you have one big wire and the current goes from - to +, following the current that way the spin is counterclockwise. now we make 2 sharp bends of 90 degrees in the wire so the same wire forms the "water or short cirquit" and the way back. the rotation will be the same compared to the wire but the wire goes in a different way. in the 2 paralel ones this results in the spin coming together on the bottom and parting on the top on the inside of the just created loop, this creates polarity, the midle piece between the 2 bends does the same and so generates a force on itself because they all want to repel eachother,

[daan V L]

you should add what side is + and what side - because when talking about the current direction the 2 most used explainations are completely oppisite, in high school and on many normal people places it is told as if it goes from + to - however in college and professional workflows it is typically from - to + instead.
since this article can be both, it is now very unsure what side should be + and what side -

when looking to a railgun which works in a similar way if the + is on the right rail and the - on tha left rail it will move foreward, this is because when the magnetic field rotates around the wires it means that in between the wires and the spin adds up forming a stronger polarized magnetic field where on top you get one pole and the bottom another, the projectile also does the same and the opposite, on one side of the frojectile the current will be the same, the other side is neutral or opposite..

[knyque]

I would assume the bubbles would make some noise, especially if this was a much larger scale. I wonder if it's possible to remove the bubbles, or keep them from forming in the first place.

[Polymorph]

Lower voltage, greater surface area, stronger magnetic field.

[ELECTRONFLYER1]

I AM NOT CLEAR ON WHY THE WATER MOVES. IS IT BECAUSE OF IONS OR SOME OTHER REASON.

[JohnC430]

just like in a rocket motor the fiery stream of hot air pushes against the surrounding air, and moves the body of the rocket, in this case it is the salt water acts like the fiery stream of hot air and pushes against the surrounding water and moves the magnets forward. Maybe I did not express this clearly but just think about it with this clue.

[Polymorph]

A rocket does NOT push against the surrounding air. How would it work in a vacuum, then? The thrust comes from pushing mass backwards, not from the exhaust pushing against the water around the sub.

[AaronH88]

When current flows at a right angle to a magnetic field, motion occurs at a right angle to both the magnetic field and the current flow. Rather than current flowing on a wire, the salt water is the current carrier (conductor).

[knzio]

Could it be faster if the outlets were smaller?

[KJMagnetics]

Maybe some kind of venturi effect? We're not sure, but it might be worth trying!

[knzio]

Yes, have a look at this: https://en.wikipedia.org/wiki/De_Laval_nozzle

[DavidL868]

The de Laval, or converging-diverging nozzle only applies, in the context of affecting thrust, to compressible fluids near the speed of sound.

[DiegoF3]

I was thinking the same! Perhaps there is a limit?

[rstaceyjones8ckn]

This is not magnet powered, it's battery powered.

[aldolo]

brilliant

[banman11]

Great project! I like it.
Would incorporating a boost converter circuit to up the voltage give you significantly more thrust?

[lang.wilson]

Does more voltage mean more speed?
Or would you need bigger magnets as well?

[kmpres]

Apparently, from the discussions above, more voltage will yield more thrust, but also more bubbles which will reduce thrust. The voltage level just before when bubbles appear seems to be the sweet spot. In a real sub bubbles would give away a sub's position to the enemy, both visually and aurally making stealth impossible, so a careful balance would need to be maintained, assuming of course this tech ever becomes practical for a real sub.