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Old 11-11-2021, 09:49 PM   #11
whswhs
 
Join Date: Jun 2005
Location: Lawrence, KS
Default Re: Help me stat a steam thrower weapon

I don't agree with 2d burn. Damage from molten metal is 3d, but damage from flames is only on the order of 1d, and this live steam is not going to be hotter than typical flames, nor enough denser to have more heat content.

If you want to work with its being under pressure, I would treat it as doing a combination of cutting and burning damage. I might have the majority of the damage be cutting, with perhaps +1 from burning; I've had a couple of burns from steam, and while painful, they probably didn't do even 1 point in GURPS terms, so I think hotter steam might not do so. But at most I would allow 1d burning on top of the cutting damage.
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Old 11-11-2021, 11:58 PM   #12
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Default Re: Help me stat a steam thrower weapon

My goodness Bill, I hope you weren't exposed to super heated steam for too long, it's known for cutting broom handles in half.
Normal industrial plant steam is in the order of 600 psi, and when pipes rupture then can be deadly, such as:

In an incident in a New York City high-rise building, seven people were scalded to death at their desks when an HP steam pipe in the wall ruptured.
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Old 11-12-2021, 12:13 AM   #13
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Default Re: Help me stat a steam thrower weapon

I think there are two answers depending on the question you are asking.

If you're looking for a realistic design, then it will not work. The power and insulation requirements to generate enough steam to do the kind of damage you want would warrant a room full of equipment, rather than being man-portable. You might get something useful by using the steam to shoot projectiles, but even that would be marginal.

If you're looking for something non-realistic, great! It works by GM fiat. Just make sure the numbers are not too out of line compared to what is available in the setting. If guns and ammo are common, the stats you have are a bit low. If guns and ammo are not common, the stats seem about right.

If you wanted, you could always introduce some sort of weird science material that makes this (and potentially other) things possible. Sort of like what Deadlands did with ghost rock.
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Old 11-12-2021, 05:47 AM   #14
whswhs
 
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Default Re: Help me stat a steam thrower weapon

The cutting people in half part, at least, is not something you'd get with burning damage; it sounds like cutting damage, which is what I suggested the damage from high-pressure steam ought to be represented as for the greater part.

As for scalding people to death, that seems comparable to killing people with flame. But in GURPS, the damage from being immersed in flame is 1d-1 per second. That was what I suggested as an upper limit for the burning damage from steam, for rough consistency. That damage will add up—on the average, to 8 points every 3 seconds—but it won't kill you instantly; an average person will have to roll vs. HT to survive after 7.5 seconds. That's probably realistic, but in any case, it seems consistent with how GURPS handles burning damage. Maybe 1 point from ordinary steam, and 1d-1 from superheated steam, as burning damage, with added cutting damage in the latter case.
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Old 11-12-2021, 06:26 AM   #15
Willy
 
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Default Re: Help me stat a steam thrower weapon

New to this thread, but I ask myself if anyone has thought about the fact that if you boil water regardless of the pressure, the steam ist not only denser than hot air of the same pressure aka more heat is delivered to the target, but there is a BIG catch for the victim. The steam will while hitting the target and delivering heat, become fluid once again, therefore stick to it ( like a molotov cocktail ) and therefore delivering more heat and damage than before.

I know a bit of what I speak in my youth I worked in a factory which powder coated surfaces, getting the stuff out of the walkable oven, still running full power, and therefore having at the skin near 150°C of hot air was in a short time no problem, no special protective gear needed, besides the shoes you could do it in shirts and short trousers. Normal steam at a kitchen has less °C, but I wouldn´t hold my hand in it.

Last edited by Willy; 11-12-2021 at 06:27 AM. Reason: spelling error
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Old 11-12-2021, 07:25 AM   #16
Turhan's Bey Company
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Default Re: Help me stat a steam thrower weapon

There does seem to be a questionable leap from "superheated steam is very dangerous," which is unquestionably true, to "superheated steam is very dangerous in this very specific way," which is, I think, what's tripping people up. And, again, if you want this weapon in your campaign, by all means do so. It doesn't have to be realistic, and if you think it is, you don't have to convince us. It's your game.

That said, if you're looking for something slightly less dubious (I mean, beyond problems with the backpack steam chamber), let me suggest something for which there's demonstrated proof of concept: a steam cannon. The basic idea is outlined and stated in Fantasy-Tech 1: A metal chamber is heated and a bit of water injected. The water flashes to steam, and the resulting explosive pressure propels a projectile. Modern experiments with the technique provide performance similar to a .50 caliber bullet. Fantasy-Tech has stats for a cannon-sized version, but if you're hand-waving the backpack unit, that concept could easily be applied to a portable version.
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Old 11-12-2021, 07:30 AM   #17
Fred Brackin
 
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Default Re: Help me stat a steam thrower weapon

Quote:
Originally Posted by Turhan's Bey Company View Post

That said, if you're looking for something slightly less dubious (I mean, beyond problems with the backpack steam chamber), .
The steam chamber is probably the msot dangerous thing to the user (specifically the part whe it builds up and then holds the pressure) but the weak link in the superheated steam projection system is the flexible hose connecting the chamber to the wand part. There's no way that's going to withstand the same pressures as the chamber.
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Old 11-12-2021, 08:09 AM   #18
Varyon
 
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Default Re: Help me stat a steam thrower weapon

Quote:
Originally Posted by Fred Brackin View Post
The steam chamber is probably the msot dangerous thing to the user (specifically the part whe it builds up and then holds the pressure) but the weak link in the superheated steam projection system is the flexible hose connecting the chamber to the wand part. There's no way that's going to withstand the same pressures as the chamber.
Part of me feels it would be interesting to get rid of the hose and wand - rather, you've got a solid tube of (heavily-insulated) metal coming forward from the backpack with a release trigger on it, allowing the character to quite-literally shoot from the hip.

Alternatively, you might be able to merge this idea with that of a handheld steam-cannon. Have a backpack of lower-temperature steam, with a hose connected to a large "wand" that has part of it highly-heated (like the chamber of a steam cannon). Pull one trigger, and it injects steam from the backpack into a reservoir on the wand. Pull the other trigger, it opens the reservoir to the heat source and the exit, and you superheat the steam, either for a brief burst of water-cutting or to propel a projectile. The two-trigger system (necessary so the superheated steam doesn't flow back into the hose, destroying it) might give the weapon RoF 1(1), although sufficient training (I'd probably just make it a Perk) would let you fill the reservoir and attack in the same second, for RoF 1.

As for the general idea, it's really not a realistic weapon, but it's a freaking steam-powered water cutter. Provided the campaign is cinematic/quirky enough for it to fit, that's a very interesting and cool signature weapon for a post-apocalyptic character. You could also potentially create attachments to allow it to use the pressure to fling projectiles at enemies.
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Old 11-12-2021, 08:21 AM   #19
clu2415
 
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Default Re: Help me stat a steam thrower weapon

When you hear stories of a steam leak cutting a broomstick in half, that was a steam line pressurized to 1 000 psi. The question becomes how are you going to build a vessel and flexible tubing that can contain 200, 500, or 1 000 psi? Secondly, how much fuel will you need to heat and pressurize the water?
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Old 11-12-2021, 08:31 AM   #20
Anaraxes
 
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Default Re: Help me stat a steam thrower weapon

Dictionary of Danger (GURPS Action) has some rules for heat. The 4d specified in the OP rates above "interior of industrial kiln" or "thermite fire" (3d/s) and below "interior of huge foundry furnace" or "unshielded reactor" (6d/s). So that seems overly optimistic for the parameters in the OP.

Fooling around with some online calculators, for the 1 qt bottle at 250 C in the OP, I get a heat loss about 35 C per hour, assuming the bottle is a squat cylinder about twice as high as it is wide and that it's wrapped in an inch (2.5 cm) of fiberglass batt insulation (because post-apoc salvage), and that it's full of water (a kilo). You could be issued your ammo before a battle, but not pack it around with you while hiking for a couple of days. Damage would decline over time; after six hours, it's down to at worst the "touching a hot radiator" level, 1 point of damage.

Also, that's about a 20% increase over the thermal energy radiated by a human, so the steamthrower will be pretty visible to thermal imaging devices. And probably extra uncomfortable on a hot day.

Not my area of physics, though, so those results are worth checking.

(I assumed the weapon-wielding isn't actually carrying the heat source with them, operating while they run around and fight. That would be more wacky steampunkish, for sure.)
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