I'm not sure Vstep has the time to model engine rooms etc. Herkules Atlas was made by a user, Vstep has all of the game to do as well. To model an engine room, you have to get the player to the door of the engine room, which is very tricky for larger ships. Plus you have to model the room itself (The H.A's engine room is actually modelled above the vessel, and made invisible when looked at from the boat. That's why you sometimes see the flashing 'exit engine room' buttons in the sky.) then you have to link the two with an interactive button.
Of course, an engine room will be quite a complex model in terms of poly's, and if the ship is already complex, then it will slow things down even more.
So, in short, don't expect an engine room in the Ocean Star or Titanic. Possibly with a smaller vessel like Red Jet 4 or RPA12, but not on anything big.