This section contains pictures and descriptions of the MHD motor, static display and boat which I used in my presentation.

Firstly, you need to see how many batteries you need to carry on the boat. By experimentation and calculation it was found that the force produced by a current of 3A, supplied by a 9 volt battery, would do nicely. Is 9 volts enough to produce this current in a saturated salt water solution?

Use R = d/(A) where d is the distance the current travels

A is the cross sectional area of the material in which the current is traveling

is the conductivity of the material

In this case the material is a saturated salt water solution and:

d = 0.04 m is the distance between the electrodes

A = 0.0008 m² is the area of an electrode = 22.6 (m)^-1 for saturated salt water at 20 deg. Celsius

Carrying the calculation through to get R = 2.21 . Now use Ohms Law: V = IR where I = 3A (short-circuit current of a 9 volt battery) V = 6.64 volts So a 9 volt battery should do the job.

If the water is not saturated, which was the case with my project, you might want to put some more batteries in series. (I had 3 in series; on the heave side)

The Motor

The Static Display

The Boat was made out of a large piece of plastic Styrofoam and looked a bit like a barge.

The motor was attached to the bottom by the copper rods (see above). The batteries and switching mechanism (to switch the polarity of the electrodes) were contained in a waterproof Tupperware container mounted on top of the barge.

(Sorry, no picture due to technical difficulties. You're just going to have to imagine it.)

Back to Main Menu