Terminology: Starship compartment numbering conventions

image (c) iurii/ shutterstock

image (c) iurii/ shutterstock

Category: Terminology – starships

= Compartment numbering conventions

Dirt treaders boarding a starship for the first time are usually confused by the compartment numbering conventions. You’re asked to report without delay to compartment A02-02-05. Where the hell is that?

The problem is worse for sea sailors and atmosphere flyers, because to them, the life of a starfarer is twisted out of whack. Specifically, 90 degrees out.

Here’s why.

Most starships are roughly tube shaped. The shield projector is mounted in the bow, and extends a magnetic field at high speeds to deflect the interstellar medium harmlessly around the sides. The main engine or engines are mounted in the stern. There will be attitude adjusting maneuver engines mounted at other points, but the main engine provides the thrust to reach the interstellar cruising speed of half lightspeed or more.

Starships do not produce practical amounts of gravity. However, when the engines are thrusting, a reaction force is experienced that feels like gravity. On a planet the analogous reaction force pulls you down toward the planet’s center; on our ship the force pulls you back toward the stern.

The ship will spend most of its journey time cruising, not accelerating. Without thrust from the engines, the ship will experience what is commonly referred to as zero-gravity, freefall, weightlessness, or zero-g.

In terms of ship layout, that means the crew (and equipment) spends most time in zero-g, but will experience periods of pseudo-gravity in which the aft bulkheads (those facing toward the back of the ship) are perceived as ‘down’.

The simplest starship layouts have decks running from the bow down to the stern, and frames running perpendicular to the decks from the top (ventral) hull down to the lower (dorsal) hull.

[See variant frame design for alternative designs. For simplicity, we have referred to frames as planes running from the ventral to the dorsal hull. In practice there is often no ‘top’ or ‘bottom’ to our ship tube, other than arbitrary labels used to help us navigate the ship layout. Nor do frames or decks need to be planes. For example, some starfarers who evolved in their home planet’s oceans flood their ships and navigate the craft’s interior with reference to artificially induced currents. For that matter, some ocean dwellers do away with frames altogether, the strength and rigidity that frames give the ship’s hull being provided by the combination of support struts and the resistance to compression of the pressurized fluid medium they live within.]

Starship layout is different from waterborne ships where decks are a series of horizontal planes running from the main deck down to the keel, and frames that are perpendicular to decks, running from bow to stern.

Thus to a water sailor, the layout of a starship looks at first like a tall office block tilted on its side, and with an engine strapped to its base. The crew either floats in weightlessness or stands, miraculously, with feet glued to the wall, even though the building has been tilted through 90 degrees. Once our hypothetical sea sailor actually boards a starship, his or her mind readily acclimatizes to the new reality and it will soon appear as if it is the waterborne craft that are unnaturally tilted on their sides.

Let’s take Beowulf as an example of a famous ship with a standard layout. Beowulf’s decks run from 0 (bow) to 20 (stern). Like many ships, Beowulf has nacelles (housings separate from the main part of the hull). Decks on the port and starboard nacelles are A00 through A06, and B00 through B06 respectively.

There is no equivalent to the water ship concepts of forward perpendicular or aft perpendicular, and so frame numbering is simply from 00 (port-most) to 16 (starboard-most)

The third compartment identifier refers to an imaginary plane running through the center of the ship, as measured from its upper (dorsal) hull down to its lower (ventral) hull. Number sequence is outboard (running from amidships out to the ventral/ dorsal hull). Odd numbers are on the dorsal side and even on the ventral side. The first compartment on the dorsal side of the centerplane is 01, the second 03, third 05 and so on. The third compartment to the ventral side of the centerplane, for example, is 06 (being the third even number). Beowulf’s run from 01 to 19.

Remember, we’re talking about the simplest layout for the purpose of illustration. The concept of a dorsal and ventral hull makes no sense in some alien ship designs, but with most human-crewed ships, it is possible to nominate one face of the outer skin as being the upper/dorsal hull, and from there locate port and starboard beams and ventral hull.

Neither frames nor decks always run the length or breadth of the ship (especially ships with nacelles) which can be confusing. Starting amidships and moving to port, it appears that frame numbers are being missed. For example, compartment, 03 in particular can often appear to jump on the Beowulf.

Finally, many ships also employ a fourth coding attribute that identifies the usage of the compartment.


So, to take an example of Beowulf’s compartment A02-02-05

Deck A02: Is in the port nacelle (second deck aft of forward-most)

Frame 02: Is third deck in from port hull.

Number 05: Is on the dorsal side, roughly a third of the way ‘up’ from amidships.


If you find this confusing, you aren’t alone. Take a map! Navy crew often delight in using the confusing layout of their home to bamboozle Marines newly embarked on their ship. Remember that they have probably lived their entire lives never having ventured more than a hundred meters outside the ship’s hull.



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