Mechanism for Emergency Ballast jetison.

[EdwMullin@aol.com]

I was flipping through an industrial supplier catalog today, and I found some
DC electric magnets.  They use twelve volts and some can carry over 1000 lb.!
Some had a spring loaded release to aid in dropping the metal being held. I
was thinking, if these were mounted to the exterior of the hull then steel
plates could be used as ballast.   I would think that some advantages would
be: 
1) Ballast would "automatically" jettison when battery power falls below
minimums.
2) No way for a release mechanism to jam or stick.
3) One through hull for the power for probably as many points as needed. 
 
Disadvantages:

1) reduces battery duration
2) adds complexity(some)
3) means of retaining ballast when power is off... 

Has anyone heard of, or tried a system like this? Any thoughts on if it would
be worthwhile??