The steel box (ship) may provide pretty good EMP protection depending on lots of unknowns. We pretty much know what will happen if an EMP hits the electric grid because those long transmission lines make excellent antennas and feed lines to transformers and customers.

A very good point I hadn't considered.

A boat (especially w/zinc plates) discharges static electricity into the water very efficiently. A large charge can be discharged through the hull very quickly. Radios, RADAR's, and other pieces with external antennas may be fried but the internal computer monitors and generators may be very well protected!!!

I'm doubtful of those vessels equipped with CAPAC Systems as they are proven lightening attractors with the subsequent electronic damages well documented. Those vessels don 't lose internal control systems though, to the best of my knowledge and experience.