While my group is waiting between book 3 and book 4 of Dead Suns, I was planning on doing a little homebrew adventure where they encounter a distressed passenger cruise ship. Unfortunately, the ship I built with the rules as written was just absurd. Huge ship, barely over a dozen passengers. I envisioned about fifty to sixty passengers, twenty ship crew, and a dozen steward staff.
To get this result, I made some homebrew expansion bay rules. I essentially assumed the bays listed in the book (except for the hangar bay and shuttle bay) are medium sized bays and only fit medium sized ships. I made it so larger ships had larger expansion bays.
I have a word and pdf of what I came up with, but it doesn't format nicely on this messageboard. I'm going to see what I can do the get it too look right before I post it
Although specific expansion bays may vary in size, the following volume lists the average size of the different size bays
Tiny 150 square feet (typically 5x5x6)
Small 1,200 square feet (typically 10x15x8)
Medium 10,000 square feet (typically 25x40x10)
Large 80,000 square feet (typically 50x80x20)
Huge 600,000 square feet (typically 100x200x30)
Gargantuan 5,000,000 square feet (typically 250x400x50)
Colossal 40,000,000 square feet (typically 500x1000x80)
In each of the expansion bays, an entire bay must be devoted to the same type. It is possible to fit smaller bays into a larger space, but a lot of efficiency is lost due to the need for extra structure, hallways, power conduits, different support units, and the like. A larger bay can only be split into two bays each one size smaller, or three bays each two sizes smaller. Smaller divisions are rarely included in ship design.
I can't really get the results to format all at once, so here is just a sampling for cargo holds and guest quarters (good)
Cargo Holds: all are 0 PCU and 0 BP. Here are capacities (in tons) based on size:
Tiny 0.4 tons (800 pounds)
Small 3 tons
Medium 25 tons
Large 200 tons
Huge 1500 tons
Gargantuan 12,000 tons
Colossal 100,000 tons
Just for reference, 25 tons is the gross weight of a typical 8x8x40 shipping container. The biggest container ships are about 1200 feet long and carry about 20,000 containers for 500,000 tons of cargo. I imagine that the merchants of Starfinder are smart enough to employ a similar technology.
For Guest quarters, the following numbers are listed by passengers/PCU/BP
Small 1/1/1
Medium 4/1/1
Large 8/1/2
Huge 15/1/3
Gargantuan 30/1/4
Colossal 60/1/5
Although keeping the PCU the same might seem odd, it's because the environment is kept the same, and the increase in personal usage is insignificant on a spaceship power scale.
Here's the stats of the cruise liner (many thanks to James Turner for his excellent ship builder!)
Princess of the Sun (Tier 9)
Majesty class liner; Sanjaval Systems, Akiton
1250 feet length, 2600 tons
Huge Bulk Freighter
Speed 6; maneuverability poor (turn 3); drift 2
AC 18; TL 20
HP 200; DT 5; CT 40
Shields Light 80 (forward 20, port 20, starboard 20, aft 20)
Attack (forward) heavy laser array (6d4)
Attack (aft) heavy laser array (6d4)
Attack (turret) linked light particle beams (6d6)
Power Core Nova Ultra (300 PCU); Drift Engine Signal Booster
Systems budget long-range sensors, crew quarters (common), mk 1 armor, mk 3 defenses, mk 2 mononode computer (tier 4); Security anti-hacking systems mk 2 (DC +2), biometric locks, computer countermeasures (alarm, firewall, lockout)
Expansion Bays cargo hold, guest quarters (luxurious), guest quarters (good) (2), shuttle bay, recreation suite, escape pods (3), life boats
Modifiers +2 any one check per turn
Crew complement 25, service staff 15, passengers: good quarters 30, luxurious 8
Cargo capacity: 1500 tons, escape pods 75, life boats 16, *shuttle
Listing cargo capacity in tons seems like an odd choice, given that cargo will weigh 0 tons with the thrusters off and in general have weight dependent on the ship's thrusters. However, I approve very much of giving larger ships larger expansion bays, to avoid problems like how you can make expansion bays on Huge ships larger by putting a hangar bay in, then putting a shuttle in the hangar, which turns any 2 expansion bays into 3.
I found a similar adjustment was needed for larger ships and escape pods/lifeboats. Unless every sentient species that required life support decided that a standard of 'we should probably have enough pods and stuff for the entire crew' was not really an OSHA standard they needed :)
Escape pods shouldn't even require a bay, only BP; in a lot of media, the escape pods are just mounted to the outside of the ship with a hallway running by them.