The internal structure of our ship is often important, unless it’s so small as to have little more than a room or two. Characters need to move between locations such as the bridge, cargo, engine room, and quarters. We don’t write about mundane scenes but active ones where the speed of transit is a factor in how the scene plays out. If it takes five minutes at a full run to reach the spot where aliens have breached the hull, and it will only take two minutes for the aliens to destroy the life support systems located there, we’ve got problems. Taking time to plan out our ship’s structure (to some degree) is helpful for not only understanding such scenarios, but imagining them in the first place. No structure is foolproof, as organizing things to avoid one problem will likely cause another, so thinking about our story needs can help us build a vulnerability into our vessel.
Certain realities exist on many ships, such as living quarters being near dining areas. Crew typically have smaller quarters in poorer locations than passengers, except for captains and officers, who may still not enjoy great privilege. Most vessels will need propulsion located primarily in the rear, an area often reserved for dirty or less desirable conditions such as cargo holds, loading areas for both supplies and sometimes passengers and crew, and machinery to power everything. The bridge or command center is typically forward.
Vessels which travel on water load from lower decks, especially for cargo, so the ship does not become top heavy; cargo acts as ballast and should be lower anyway. Also, loading from above just means having to create buildings and ramps to lift potentially heavy items unnecessarily. In space, this consideration is gone, but a ship designed to enter an atmosphere must still be balanced internally, whether that’s front to back or side to side. In a weightless environment, heavy items could theoretically be anywhere, but artificial gravity is seemingly never lessened in areas with heavy cargo. Regardless, one could presumably float cargo to its location with relative ease.
Consider the purpose of our invented vessel before creating its structure. Passenger, cargo, and war ships will share areas like a bridge, engine room, and crew quarters, but entertainment, storage, and weaponry will all differ in size, quantity, and placement. Ships that are intended to permanently remain in space do not need aerodynamics.
Do We Need to Invent Structure?
In video gaming, a ship’s internal structure is crucial because the gamer will typically guide a character room by room through the ship. It should make sense even if the layout or the purpose of rooms is not explained or apparent to someone who’s busy killing NPCs onscreen. World builders are advised to plan a detailed internal structure so that the graphics team can implement it.
But in books or movies/TV shows, the structure often seems irrelevant. Seldom do we follow a character from a room, down a hallway, and to another room; doing so wastes precious screen time. I’ve seen entire series runs of Star Trek and still had little to no idea where one section of the ship is in relation to another. Even so, if we’d like to be consistent for a ship we’ll use often, decide which deck each major department you’ll mention is on. This avoids indicating that engineering is on deck six in one book and on deck seven in another. We don’t need to be more specific than which deck and whether fore, aft, port, or starboard, if we really don’t want to. Having a sense of difficulty and/or speed of access from various other places on the vessel is more important. If creating internal structure helps us do that, then yes, make decisions.