It works well at small scales, but you still have the power problem: torpedo's usually have less of it available than subs.

The magnetic parts can, depending on the design, be shielded. It would certainly be possible to limit the magnetic field in the case of a MHD duct going through the ship. For external MHD drives, it would be harder.

http://syd.mech.eng.osaka-u.ac.jp/pa...94/05_IMDC.pdf
http://www.mesj.or.jp/mesj_e/english...n011995p46.pdf

Wikipedia also may be useful for some links related to magnetohydrodynamic systems.

Thanks for the reply guys...had computer problems so could not log on for a while.

Someone mentioned that cavitating will cause propellor "pitting" and make it noisier overall. Though DW doesn't have this does it? I thought I read somewhere you can pick up noisy ships with damaged propellors in DW...though I might be imagining it (probably aren't any in game).

As a VERY rough rule of thumb if your speed squared e.g.10kts Squared=100,exceeds your depth you will cavitate.