Jeff (Siegel) argued successfully I believe that a blue water skipper could just put his iPad or Android device inside the microwave which would act as a Faraday shield during a lightning strike so it would survive. I haven't tested that theory yet
Jeff is a brilliant man, but we have disagreed on some things--and I believe that using a microwave as a "Faraday cage" for a lightning strike. would be one where I would disagree. The problem would be if one were not to disconnect the microwave and the oven begins to disintegrate and even catch on fire (which has occurred with lightning strikes). The second issue is that the microwave shielding is to prevent specific wave lengths (about 2.45 Ghz) from escaping and causing harm to humans, including interfering with pacemakers and other electronics. Many other frequencies will penetrate a microwave oven, even if it remains intact. This has been discussed on several physics forums, and generally it is felt that the microwave oven only attenuates EMP, and may not give as good protection as a true Faraday cage.
An EMP of the "right type" could take out the GPS satellites--either partial or all
I took a different tact--l before chart plotters were affordable. I put a hand held GPS in a metal ammo box (and double seal, with aluminum duct tape), which was not connected in any way with any of the electrical circuits on the boat.
I was in a very large Faraday Cage earlier this year, at the Wende Museum of the Cold War, which is the old National Guard Armory in Culver City. They had constructed two about 10 x 12 rooms for storage of radio gear, computer electronics, weapons and ammunition during the cold war.
I printed out charts of the Cumberland River for Last year, but rarely used them. I found that the actual chart books by COE (about $20) were far better to use than the binder full of 8 2/1 x 11 sheets). The other issue with PDF charts is having to stitch together the chart from the separate sheets (which I have done).