Long post / tangent warning. You know I've been working on simplifying FF&S right?
Calculate the surface area of your box, multiply by 1 cm, divide by the toughness of your material
This example will use FF&S-1 steel (at toughness 2.0, instead of the 2.86 in T4 / FF&S-2). For the aformentioned 2mx2mx3m box, the surface area is 32 m2, volume is 12 m3. For steel the internal structure volume is 0.016 cubic meters to support 1G structure (multiply this value by the max G you want it to take)
The shell takes the same volume (0.016 cubic meters) for each 1 AV you want it to have. steel has a density of 8, so this is 0.128t (128 kilos) for an AV of 1 and for each design G. (note 1)
If you multiply this base value by 2 you have a G-value of 1 and an AV 1 shell (which coincedentally are the minimums required for any vehicle in TNE)
For comparison, that's about 500 pounds for the structure and sheet metal on a car-sized object, which strikes me as a bit high but within the realms of believability.
an AV 10 shell is required for a spacecraft, and as written you need 10 AV for each G that a starship hull can produce (note 2)
As an aside, composite laminates are the lowest tech material I'd reccomend for hull materials on anything using mass-based thrusters, and crystaliron is where military hulls start to make sense (and bonded superdense is where you need to go for hulls that will actually stop lasers...)
This is so conceptually simple it boggles the mind that it wasn't explicitly worked through in FF&S (all of the base volumes are for spheres, which you can derive using an Excel spreadsheet) As a result it's too easy for most folks to grasp. FF&S noticed that hull designs were complex, and figured that most people would rather just have a formula (however baroque) to determine their hull and structural volumes without actually going into what they were doing, and making it difficult to build "custom" dimensional hulls (so figuring out the *actual* hull volume instead of fudging it)
If you want to do the math, there are significant volume savings to be had for hulls of more than 50 cm thickness. This is actually an issue for some of my orbital fortification designs
My rule of thumb is that if the armour thickness exceeds 1% of the smallest dimension of the hull I should probably put in the extra work and save a few Dtons.
Using the above box as an example, if you want 50 cm of hull armour it would take 16m^3 (32 square meters x 50 cm) for armour using the "base" system (more than the actual available volume!) but the actual internal volume leaves a 2 m "void" in the middle for 10 m^3 of armour.
"Structure" volume doesn't change, although for an example this extreme I'd calculate the structure based on the percentage of non-hull volume (saving 83% of the "structure" volume based on the assumption that armour plate has sufficient structural integrity without adding bracing to it. This is not worth the time to do with a real hull design, since the volume is generally less than 1% of total volume, even for lots of armour)
Scott Martin
Note 1:
but wait, don't we have G-Compensators? If the people don't have to take 6 G's, why does the frame of the starship? If the G-Comp fails, then the people are probably dead even if the hull holds together...
Note 2:
IMO One of the most stupid rules to ever be introduced in a "realistic" design system. In space your maximum speed (and thus what you have to armour against) is based on your fuel reserve, not your accelleration. In point of fact, trying to armour a FF&S starship against a chance collision (or KKM) is a bit like trying to stop anti-tank rounds by wrapping yourself in gelatin
Build the hull to hold in atmosphere, hold out non-penetrating radiation and call it good. (AV 10 is a decent call, although NASA designers would love to have this amount of weight margin to play with...)
