Just thinking about what shipboard life would be like. A few comparisons:

A Nimitz-class aircraft carrier is a bit under 350m long, has a beam of about 40m (the flight deck is wider, of course), and carries a crew of roughly 5,700 including air wing personnel. She obviously doesn't have the life support requirements of a voidship, but she also has a crew that lives in conditions no Imperial Navy rating would ever see and is really never more than a week from a friendly port, often less.

Modern subs are harder to get solid info on, but they're certainly smaller (less than 200m long) and their crews are somewhere in the 150 range. They do have life support requirements comparable to a voidship, and many are designed for the kind of extended-duration service that warp journeys entail. They are extremely mission-specialized boats, and stealth is a major design limitation for them.

A Havoc-class heavy raider is 1600-1800m long and has a beam of 300-400m. Assuming a somewhat flattened hull and limited tapering, she probably has at least 12 times the hull volume of a Nimitz. She requires full life support and logistic redundancy for long voyages, but her crew is accustomed to living conditions that makes "spartan" an understatement. Her shipboard equipment is pure 40K era gothic tech, manpower-intensive and bulky but very sophisticated in some ways.

Given all that, a crew population of ~20,000 on a Havoc is not only reasonable but possibly conservative. Low-maintainance servitors might easily add half again that number and still leave room for thousands of embarked troops or passengers. Assuming the ship's useable living space is roughly the equivalent of 1 square km of current-day real estate, a crew of ~30,000 would make for a population density comparable to Mumbai, India, which is probably the highest on the planet these days. Crowded for most of us, but perhaps roomy to a hive worlder.

Cramming in up to another 10,000 or so is certainly within the realm of plausibility, but you aren't going to be evacuating any colony worlds or taking whole cities worth of slaves without a larger hull.

Argoden said:

One thing to remember is that volume alone is not a consideration. Population distribution is a factor (junior officers will likely get space averaging about that of a one-bedroom flat - less for the least important, more for those on their way up - while senior staff and the captain in particular will have quarters that would make a large house look modest... meanwhile the ratings and labourers get crammed into sleeping quarters stuffed into available space between important parts of the ship), as it use of volume (mixtures of cramped, narrow corridors, access-ways you could drive a tank down, uncomfortably small compartments and vast cavernous chambers, depending on the purpose of that particular area of the ship).

N0-1_H3r3 said:

There's also a lot of fluff supporting the idea of huge portions of ships being sealed off and unused. Such areas are often home to twisted, flesh-eating mutants or worse.

Atheosis said:

That's one part of the fluff I never really liked. Any spaceship captain worth his pay should do anything in his power to avoid that.

Dammage and accidents could make it nessecary to seal of areas, but I don't see how any mutant, no matter how tough, could live there. What would they feed on ?

Vacuum ?

Radiation ?

Crew from nearby areas ? I thought the area was sealed off. And don't give me the " They'll move through the ventilation shafts" ! any spaceship that size will have airtight, fireproof sections allowing any part of the ship to be sealed off in case of accidents, fires, asteroid strikes, battle dammage, space pirate boarding actions, mutiny, crew riots etc.

Finally all kinds of powercables, oxygen lines, data connections, water and sewage pipes may run through any part of the ship. Allowing angry flesh eating mutants near that kind of stuff is somewhere between stupid and suicide.

The captain of a ship has nearly total power, so if a section of the ship is infested with some kind of creatures/mutants and the crew can't get rid of them, he can order everyone out of the sector and de-pressurize it. It's got to be one tough mutant to survive without air at absolute zero temperature ! . . warp creatures is another matter of course :-)

Lindgaard said:

Fungi that grow on material from chemical leaks.

N0-1_H3r3 said:

Oh sure, absolutely. Officer's Country is going to be relatively palatial, while many ratings live and work in the most cramped of conditions. Just like a city, there are dramatic variations in how crowded different areas of a ship are. Still a useful number for benchmark descriptions. Captain's digs, think Buckingham Palace. Rating hab-block, think the streets of Kowloon.

Atheosis said:

How much of that is voidsman superstition is unclear. Some ships are certainly officially unpopulated, and there's a good chance that any such area will have people shacking in it. OTOH, those squatters are more likely to be slackers, deserters, cultists and criminals than ravening cannibals. Spreading horror stories via the grapevine would be a good way to ensure they remain undisturbed as long as possible.

That's not to say that mutant enclaves are impossible, but I doubt they're as common as the fluff makes it seem. Even an "underground" population (like mutant outcasts) isn't likely to be completely isolated, as they'll likely have dealings with shipboard black marketeers as well as performing acts of petty thievery. They might even be tolerated to a degree if their diet helps keep the rat-and-vermin population down a bit. Plenty of meat on a rat or void-slug, you know.

I suspect that "Black Holds" where sections of the ship get sealed off and infested by mutants can and do happen, but not very often. Like getting attacked by Chaos Raiders, having the Gellar Field fail or being flung centuries into the past or future by a Warp mishap, they're a peril of Void travel. But the stories all get handed down by drunken Voidfarers in dingy bars on the lower decks for centuries after each isolated incident.

As with time displacement, the only way hordes of mutants will end up pouring out of the Black Holds to devour the crew is through GM fiat, not as a matter of course.

Lindgaard said:

Imperial ships just aren't that effecient. This isn't a nice, rationally designed ship from Star Trek. Yes you can seal off certain parts of the ship, but it isn't precise. The idea of depressurizing also doesn't really work the way you think. You can do it, but not with enough precision to only affect the desired areas. Once again these ships are not designed in such rational ways. I'm sure most Captains can and do minimize such things, but when you're talking about a ship the size of a small city it's likely that they won't be completely successful. Remember that this isn't sci-fi and the idea starts making more sense.

Well unless my math skills fail me the raider you mention would have a lot more than 12x the hull volume of a Nimitz.

That having been said you have the right of it. The ships are BIG!. As a further example let me illistrate with a lunar class cruiser. The dimensions used will be rough as the ships are of a irregular shape.

A lunar class cruiser is 5000 meters long 800 meters wide and 1200 meters tall (guess)

This makes each deck 4,000,000 square meters in size, or 4 square km, or if you prefer 43,055,600 square feet.

Now lets say each deck is an (what I believe to be a conservative) average of 10 meters tall (some would be larger some smaller). That gives us 120 decks

or a total floor space of 480 square km, 480,000,000 square meters, or 5,166,672,000 square feet.

To put that in perspective lets take the city where I was born Hartford CT. The city itself has a population of ~125,000 and is 46.5 square kilometers in size.

Scale is a hard thing to grasp.

llsoth said:

Perhaps. Depends on how flattened the raider hull is, and I was being rather conservative. If we compare cylindrical volumes the ratio's much larger, but neither ship is cylindrical, of course.