Indeed cars, airplanes, boats, all have “grounds” that are not “earthed” in any way.
Fun tidbit, old English cars (and the original Ford Model A!) used to tie positive DC to the frame rail as a “ground” or “common” instead of the negative DC. They are referred to as positive ground cars (and tractors!)
Airplanes do have static wicks [0] which could be seen as a form of local ground. I love these as an example of the adjacent engineering challenges that arise.
Busses also (used to?) have ground straps that you may see dragging. Apparently this was somewhat common on cars as well. "bus ground strap" is unsurprisingly difficult to search for, but I did find a discussion on Quora [1] that claims rubber formulations were responsible for vehicles picking up a static charge.
All of this is interesting once seen as an attempt to remove the potential difference between local "ground" and ambient environment.
Which modern cars, for example? As far as I know the era of positive ground vehicles ended roughly during the fifties, and very much by the sixties at the latest.
Fun tidbit, old English cars (and the original Ford Model A!) used to tie positive DC to the frame rail as a “ground” or “common” instead of the negative DC. They are referred to as positive ground cars (and tractors!)
https://www.restore-an-old-car.com/positive-ground-cars.html