Ok, guys, enough talk. Let's plug in a few numbers.
First of all, I'm working from a Tench docking plan (I'm building a Tench class). I can't suggest, strongly enough, that you get the docking plan, for the class boat you're building. Better yet, the plan for that particular boat.
For particular interior details you'll need the ship's plans for the boat.
The pressure hull, not counting the torpedo rooms, is a tube 16' in diameter and 176' long. That's 2 2/3" by 29 1/3", in our size. I plan to use a 2 1/2" cardboard tube and shove 2 2/3" plastic disks (bulkheads) into it, to force it to size. Since were opening one side, anyhow, this should work.
Here's where you hit the first problem. The last 16' (2 2/3"), of the bottom of the pressure hull, tapers up 12 degrees (And, slightly, inward, at the sides). So that the aft end of the maneuvering room is a 14" (2 1/3") circle. The top is parallel, to the rest of the pressure hull.
The conning tower is 8' Dia. tube, with domed ends. It's straight for 13', the ends bulge out about >2'. The main radius of the end caps is (about) 7' with a 1' radius blending it to the main tube.
In the area of the torpedo rooms, the pressure hull is the outer hull. The forward torpedo/forward battery and after torpedo/maneuvering room bulkheads meet the outer hull and so, the outer hull becomes part of the pressure hull. You'll see what I'm talking about, when you look at the plans. Those bulkheads overlap the main pressure hull. The overlap is as little as 3" (at the top of the forward room) as much as 3' 6" (at the bottom of the forward torpedo room)
If you use a tube larger than 2 2/3", cut a slot out of it and pull it into the bulkheads.
Well? What are you sittin' there for? Head for your local hobby/rug/hardware store and start looking. Let me know when you're ready to look at the torpedo rooms.
Mike K.