...for the engine to be on the lowest level, considering that's where the "paddle-wheels" would be poking out of the ship, right? Might even be a level above (in hopes of keeping the sand out, most likely) - half the level or so dedicated to engine and the rest cargo? *shrugs* I dunno... I'm no shipwright, I'm a navigator... I don't build 'em I just make 'em go places and try to keep 'em from getting lost, right?
Anyhoo... Just my inputs on the wheelhouse area, here... I kind of imagined the wheelhouse itself being located about 3/4 of the way toward the aft of the ship... one (maybe two) door leading out onto the deck and a hatch leading up to the "roof" of the wheel house where, likely, Sully's got some sort of observation platform set up (spyglass mounts, wind socks, weather vanes, etc)... Also figure that Sully's tiny little cabin is located directly beneath the wheelhouse and is accessible via a hatch in the floor not too far back from the console(s) where the levers, cranks, and whatnot used to actually steer the ship are located.
*shrugs*
Let me know if there's anything I can do to help out.