[3e Vehicles] In need of a few clarifications...

[Varyon]

One thing that gives vehicles (and people for that matter) more realistic injury tolerances is to use a semi-cumulative wounding system, and I actually intend to do just that. The primary issue with GURPS HP is how they accumulate. A good quick-and-dirty way of handling this, while it's not as realistic as some other approaches, is to determine the immediate effect of any given attack normally, but for purposes of actually reducing HP, divide it by 5 first. So a 20 HP injury on a 10 HP character requires 3 HT rolls (one to stay alive as the attack would drop you to -10 HP, one to stay conscious as the attack would drop you below 0 HP, and one to avoid knockdown/stunning, as the attack does more than 50% HP injury), but actually only reduces HP by 4 - getting hit with three such attacks is likely to render you unconscious, and has a good chance of killing you (3 death checks), but won't instantly kill you.

Of course, I'm also considering some insanity where each component has its own HP completely separate from the vehicle's actual HP, with each component giving Cover DR to the vehicle's two Core systems and its Frame. Frame is a "free" (by mass; it's distributed equally among all components and is somewhere between 1% and 5% of total vehicle mass, I haven't decided yet) system, and only damage to it counts directly against the vehicle. My current intent is to simply give the Frame HP appropriate for an Unliving object of its mass, with Injury Tolerance: Armored Flesh (basically, IT:DR where Armor Divisors reduce your level of IT:DR) based on the materials it's made from... but some work* indicates the IT:AF divisor is likely to be quite large - ultra-high strength TL 7 steel has IT:AF of 50 or so. So, an SM+5 vehicle with a TL 7+ steel frame that accounted for 1% of its total mass would have around 30 HP and IT:AF 50, giving it functionally 1500 HP (Spaceships only gives an SM+5 vehicle 200 HP), which is... problematic.

*My methodology here is to take a ~125 lb character - HP 10, and thus Cover DR 10 - and assume they have the density of water. This body is then replaced by an equal volume of the material in question and HP is recalculated based on the new weight (we use a multiplier of 2, as Cover DR is what we're interested in). As Cover DR 10 would correspond to around 10" of flesh, we multiply the material's DR/inch by 10 to determine what Cover DR it should give, then divide this by its HP to determine its level of IT:AF. For example, the Wood found in Low Tech Armor Design (Pyramid #3/52) has DR 1.5/inch and a density of 25.2 lb/cf. Replacing our 125 lb character with one made of this wood would reduce weight to around 51 lb and HP to around 7.5, and 10" means DR 15, so IT:AF is 2. For the above TL 7 steel, we're looking at DR 90/inch and a density of 486 lb/cf, for around 980 lb and a hair under 20 HP, and DR 900. This gives us IT:AF of 45, which I opted to round up to 50 (trying to keep with SSR). Building the Frame out of ablative materials (note S on the Armor Design articles) means that any damage to it is multiplied by 1.2 although IT:AF still plays a roll. For example, if we take that SM+5 vehicle from above and give it a Fiberglass Frame instead of a Steel one, it would have HP 30 and IT:AF 15 (functionally 450 HP). Hit it with a 75 damage attack, that means the attack is treated as a 90 damage attack, but IT:AF reduces this to a mere 6 HP. If the attack was from a laser with AD (2), however, that would reduce IT:AF to 7, for 13 damage.

EDIT: After calculating values for all of the armor types found in the two Armor Design Pyramid articles, I've decided the above methodology doesn't quite work - for an equal mass of two materials, the one that gives a higher DR should have a higher IT:AF, but there are several cases with my method where this isn't the case. If I instead use WM ratios (maintaining the DR 1/inch and 62 lb/cf values from above, flesh has WM of around 5.17), dividing WM(flesh) by WM(material), things become much more workable - TL 7 steel has IT:AF of 10, for example. There are still some high divisors for really good armor materials - the various nanocomposites have IT:AF 50 - but things aren't nearly as bad as they were before.