Don't use Magnetics on big ships unless you have no choice. A magnetic hit to the keel will sink most small ships aslong as it hits near the center and directly underneath it. Anything bigger than a Destroyer however will probably survive a single magnetic to the keel, so either send them in salvo's or use impacts and target for weakspots. Also Destroyers are probably the best targets for Magnetics, especially when they're racing towards you and you're in a tight spot (i.e. shallow waters)
Magnetic = lazy/quick way of firing
Impact = precise/deadly
