I’ve heard in the past and as recently as last night that “dc won’t shock you”.
Well, I’ve grabbed a plug wire at the plug and can report to you that the DC electrical system is standing tall. I had a brain fart prior to grabbing that wire.
But as to the truism, maybe I am missing something? What are these people talking about?
As you proved through your careful experimentation, DC can shock you. The determining factor is whether or not the voltage is high enough.
Boats run on 12 volts (some at 24 volts). Your internal resistance is too high to allow for a noticeable discharge through your body. But, on an ignition system, the DC voltage can be as high as 30,000 volts. (2,500 times as high as your normal boat wiring). It is easy to discharge 30,000 volts DC or AC through a body.
Hope this helps to clear things up.