Vehicle hit points

[the-red-scare]

Pretend you’re in charge of choosing the hit point system for GURPS Vehicle Design. Unlike David Pulver in the real world, you have no mandate to be even slightly consistent with established 4e vehicle stats, but do have to remain consistent with the rest of GURPS mechanics and weapon damage values. You can choose any of the existing systems or build your own.

3e: multiply surface area by 1.5, with a 0.1x to 2x modifier based on frame strength. Cars have around 200 HP, an SM +10 space cruiser might have around 150,000 HP.

4e: multiply the cube root of empty weight by 4. Cars have around 60 HP, the same space cruiser has around 1,000.

Unused 4e (from Pyramid “Extreme Damage”): multiply the square root of empty weight by 1.7. Cars have around 100 HP, the space cruiser has around 7,000.

Damage never changed from 3e to 4e, but vehicles are anywhere from 2x to 150x or more easier to destroy. I know there’s lots of ways to mitigate that via house rules, but suppose you were staring over: what kind of HP formula actually makes sense for vehicles and makes them appropriately easy or hard to kill?

[Varyon]

My own ideal would be to have a Frame for each vehicle, which is what determines if the vehicle is physically destroyed, and everything else is made up of separate locations that are damaged on their own (albeit with some possibility of bleed-through)... but I suspect that would end up being a bit complex in play.

From what's available, I'd probably go with the 4e default, but use something like Conditional Injury so damage doesn't accumulate so quickly (a 120 damage collision* being able to destroy that car is probably fine, a few dozen 1d arrows doing so probably isn't).

*On that topic, revamping of how HP interacts with collisions would be in order. As it stands, a catapulted cow does half as much damage as it would if you killed it first (Unliving objects have twice as much HP as living ones), or only 1/4th as much damage as if you butchered the cow and wrapped up the remains in a burlap sac (Homogenous objects have 4x as much HP as living ones).

[Ulzgoroth]

For the original question, I don't think you can really make one number solve the overall problem. 200 HP and 60 HP are both wrong if you're destroying a car by shooting small arms through its passenger compartment...

Really, not sure HP are a good solution for vehicles at all, and not sure exactly what problem we want them to solve.

Originally Posted by Varyon

My own ideal would be to have a Frame for each vehicle, which is what determines if the vehicle is physically destroyed, and everything else is made up of separate locations that are damaged on their own (albeit with some possibility of bleed-through)... but I suspect that would end up being a bit complex in play.

If you're splitting vehicles into a bunch of modules, why not do the same for the structure? You don't really need a 'the vehicle is destroyed' track, let the players decide whether they consider a plane with one wing, a flooded boat with half a usable engine, or a car with no roof and two wheels to be 'destroyed'.

[Varyon]

Originally Posted by Ulzgoroth

If you're splitting vehicles into a bunch of modules, why not do the same for the structure? You don't really need a 'the vehicle is destroyed' track, let the players decide whether they consider a plane with one wing, a flooded boat with half a usable engine, or a car with no roof and two wheels to be 'destroyed'.

The idea of tracking the Frame separately would be that it's a component that, if sufficiently damaged, will cause the entire vehicle to break apart completely. It's also something you can't really replace - you need to either repair it, or just cannibalize the working compartments for parts and scrap the rest - whereas doors, armor, airlocks, engines, weapons, warp drives, etc can often be swapped out, at least with a bit of work.

But, yes, often a vehicle would be rendered unusable long before the Frame gave up the ghost.

[whswhs]

I would use the 4/e rule, because I use it for characters, and I don't want incompatible mathematical models in the same game.

[Fred Brackin]

Originally Posted by whswhs

I would use the 4/e rule, because I use it for characters, and I don't want incompatible mathematical models in the same game.

I'm afraid that's what 4e already does. 20 HP is either the limit for PC humans or a 1000lb bear. That looks like two different mathematical models to me.

That's for realistic games too. A practitioner of the Sumo Wrestling Slyle from MA could have 40 hp. Thats as much as a small car.

If I thought vehicle or lare animal combat was likely to come up in an important fashion in a prospective game I was running I'd be very likely to fix it some how.

[Ulzgoroth]

I don't think anything says 20 HP is the limit for a 1000 lb bear. It's just the baseline for one in the same way that 10 HP is for humans.

Originally Posted by Varyon

The idea of tracking the Frame separately would be that it's a component that, if sufficiently damaged, will cause the entire vehicle to break apart completely. It's also something you can't really replace - you need to either repair it, or just cannibalize the working compartments for parts and scrap the rest - whereas doors, armor, airlocks, engines, weapons, warp drives, etc can often be swapped out, at least with a bit of work.

But, yes, often a vehicle would be rendered unusable long before the Frame gave up the ghost.

Some vehicles have a central portion of their structure whose loss leaves all the rest severed, but others don't particularly. A (seagoing) ship, for instance, can continue to be at least one ship if you up and chop it into two pieces somewhere along its length. Provided it's compartmentalized successfully so at least one piece doesn't sink. (Probably at most one piece will have functional propulsion in that case.)

It's probably true if your vehicle has a structural frame, you can't replace it in the sense of pulling it out and swapping another in while leaving everything else in place. Because while its out everything else can't remain in place, at a minimum. You can replace it in the sense of getting a new one and migrating all the insides over though. Or replace it piecewise in place.

[Varyon]

Originally Posted by Ulzgoroth

Some vehicles have a central portion of their structure whose loss leaves all the rest severed, but others don't particularly. A (seagoing) ship, for instance, can continue to be at least one ship if you up and chop it into two pieces somewhere along its length. Provided it's compartmentalized successfully so at least one piece doesn't sink. (Probably at most one piece will have functional propulsion in that case.)

I mean, a car tire can still serve as a wheel if the car's frame is completely wrecked, but that doesn't change that the car is completely wrecked. From what I understand about ships, they typically have keels that essentially serve as the Frame ("structural backbone" is what I often see it referred to as). Some ships don't (and I think a lot of boats don't), but for gaming purposes I think giving everything a Frame would work out better than only applying that to some vehicles.

Of course, I'm also not certain exactly how such a game system would work. It's more something I'd like to see than something I'd like to come up with myself, if you take my meaning.

Originally Posted by Anthony

In the end, 4e is dependent on DR to keep things balanced, so if you're not going to do something more radical like Conditional Injury, the easiest way to make sure large objects are appropriately tough is to give things a special type of DR that works against all attacks (even ones that normally reduce or bypass DR) of around HP/20.

Somewhere between the two (in terms of ease of use, at least) is what I think of as Slow-Accumulating Injury, which I've seen suggested on the boards before (albeit not by any name). Basically, assess things like Shock, Major Wounds, etc normally, but divide Injury by 3 to see how much accumulates. So, if an HP 10 character gets hit for 20 HP of Injury, he/she has to make a Death Check (dropped to -1xHP), make a Consciousness Check (dropped to/below 0 HP), check for Knockdown/Stunning (suffered a Major Wound), and is at -4 for Shock (took 40% or more of HP in Injury) next round. However, provided the character survives, he/she only loses 6 HP from the attack, and still has 4 HP left before getting stuck at/below 0. This essentially triples HP for purposes of accumulation, but you're just as susceptible to being knocked out, crippled, or even outright killed by single attacks. When I saw it suggested, it was more for living characters, but it would certainly help with issues like archers sinking oceangoing ships.

[Rolando]

Originally Posted by Ulzgoroth

For the original question, I don't think you can really make one number solve the overall problem. 200 HP and 60 HP are both wrong if you're destroying a car by shooting small arms through its passenger compartment...

'destroyed'.

3ed vehicles used to model/simulate this by making damage to structure only 1/10th of damage and the components of the vehicle where normally damaged, so you may shoot a lot of bullets to a car but unless you hit the engine, fuel tank or other important parts the car will still be mostly fine.

I like that, and many other details of 3ed Vehicles, but it is a lot more complicated and I can understand why most people don't want that to return.

[Rupert]

I'm tending towards the rule from The Path of Cunning, combined with the reduction in damage for attacks vs very large targets from Keeping Large Vehicles Alive (Pyramid 3-34, Eidetic Memory) which I would also consider applying to Tight-Beam Burning attacks, treating them as if they are impaling.

Also, Spaceships gives ships about 50% more dHP than you'd expect from their mass (i.e. it moves them one step larger on the Range/Speed table, which is the progression it uses for dHP). I take that as being a reflection of compartmentalisation, etc. and am considering a similar bonus to any vehicle that has features such as good compartmentalisation, trained damage control crews, vehicle-wide automatic fire suppression, and so on.

It's possible all three of these measures together swings too far the other way, and the second measure won't stop giant mecha with swords carving each other up very quickly.