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gonzo
11-15-2009, 11:27 AM
I remember reading some years ago about a quiet drive for submarines. It was suppose to ionize the water in a tunnel and magnetic coils would push the water creating thrust. Any information?
daiquiri
11-15-2009, 01:23 PM
You are talking about magnetohydrodynamic drives (MHD drives). Mitsubishi Corp. has made one working vessel (Yamoto), you can find many references in internet.
One nice site about the theory behind MHD drives is this one:
http://www.physics.ubc.ca/~outreach/phys420/p420_96/reg/main.htm
gonzo
11-15-2009, 01:39 PM
That is a very interesting link. Are there any pulse drives?
hoytedow
11-15-2009, 03:29 PM
en.wikipedia.org/wiki/Magnetohydrodynamic_drive
daiquiri
11-15-2009, 07:26 PM
I am really not aware of any pulse MHD drives used for marine propulsion. It doesn't mean that there are none of them, of course.
The problems that need to be resolved in order to make them really practical are still many. The propulsive efficiency of MHD drives is proportional to the square of magnetic field applied. Ordinary magnets produce fields of the order of 0.01 T (Tesla). Yamato had engines with superconducting magnets mantained at -250 °C which could produce 4 T field. And yet, with all that effort and complications, the propulsive efficiency attained was only about 1.8% at 8 kts !!
It has been calculated that in order to obtain the propulsive efficiency of 60% (equal to a mediocre propeller) at a speed of 10 kts, a magnetic field of 10 Tesla is required, which is a huge value and requires the use of some extremely costly technical solutions. You can compare it with a max. 3-4 T field achieved by hi-tech magnets used in hospitals for magnetic resonance imaging.
So, be it pulse or non-pulse drive, the practical use of this technology is still part of very remote future, imho.

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