Had one designed
Just, when I left the Navy, I didn't have the resources to build it. I'd certainly learned all I needed to know though to make the thing work. It was to be a small 2-person craft with multiple power sources (battery and gas or diesel generator with a snorkel).
I think it'd be a huge kick to have one. One problem with them though is that, unless you're in sparkling clear water, there's really very little to see below. Most inland lakes are very murky.
Art