That's true, but 33megajoules is almost exactly the amount of energy in 1L or 1/4Gal of gasoline. I don't know how much explosive a typical ship mounted canon requires for propellant and payload, but even given all the inefficiencies turning gasoline into electricity Id be quite surprised if there's quite a bit less energy on board to supply the rail gun.
Re:Navy Sets World Record With Rail Gun
by zitterbewegung on Saturday December 11, 2010 @12:45AM
(#1994283)
200 pound of tnt is 30.2 mJ in the M107 round you have 14.6 lbs of tnt in that shell. So basically 14 shells would equal about that many mJ. I'm sure that the ship has more than 14 shells.
If, on the other hand, you take out a magazine, you liberate an amount of energy equal to all the shots the ship is capable of taking ALL AT ONCE.
The energy necessary to fire all those shots is probably still on board, but it is likely in the form of a nuclear pile in the reactor, which is shielded up the wazoo. Even if the ship is running a conventional generator, diesel fuel doesn't have a tendency to explode in quite the same way as gunpowder.