Looking at the lower ship, the stern ‘thing’ seems to be a solid piece pivoted near the steering oar and with two rope ladders or similar holding it up. My best guess is that it is a loading ramp that can be let down to a beach for easy access to the deck.
Many moons ago I was once assured by a professor at UCSD that the “widget” was a sort of kickstand for when the boat was beached. He said it’d keep the boat level, rather than having to be laid on one side or the other, as well as used as a primitive bowplane, to keep the bow from riding too high when going over a wave, which could cause the keel to break in rough conditions.
I have not idea if any of that is true or even makes sense, not my specialty, and probably not a help.
I think you have a lot of options, and I don’t see why you can’t have a variety of ships. I’d stay away from those that are of “ancient” design as that seems a bit too far back for what Howard would have had in mind.
"I saw this in a cartoon once, but I'm pretty sure I can do it..."