Help me stat a steam thrower weapon

[Rolando]

As a side idea this may be an interesting perimeter defense system for a location with abundant water, enough energy, and some form of furnace.

[The Colonel]

Originally Posted by Rolando

As a side idea this may be an interesting perimeter defense system for a location with abundant water, enough energy, and some form of furnace.

A ship, for example - in the George G. Toudouze story Three Skeleton Key a steam lance is used against a swarm of rats to considerable effect. I'm sure there are other examples to hand in popular fiction.

They might well also appear in a Zeebrugge Raid type scenario where equipment generally used on ships is turned to port defence... or a train, armoured or otherwise, might have some kind of anti-boarding device using steam from the locomotive to rid itself of unwanted passengers. Anything within the Arctic or Antarctic circles might carry steam lances for de-icing (consider the extra topweight of ice that ships on the Artic convoy runs accumulated), otherwise they're probably used to remove fouling or purpose built.

[johndallman]

Originally Posted by Green-Neck

My GM is going to run a post apocalyptic game and I'm trying to give my character an interesting weapon. The campaign is semi cinematic and set in near-ish future Australia.

I'm imagining a weapon that looks much like a ww2 flamethrower, except it uses solid fuels like wood and coal to heat water to superheat steam.

I'm thinking of a 30 pound backpack with wand. A brazier that preheats a water tank, then fills a one quart steel tank that heats to about 250 C/480 f, that's about 40bar/600 psi.

The tank would have a temperature solenoid and thermo-electric-generator powered fan to moderate the fire.

This is very cinematic. The things that stretch suspension of disbelief with a little knowledge of steam engineering include:

• Superheating is a process of getting more heat into steam, after it has become steam. It needs to be done separately from boiling the water, because if it isn't, you just boil more water. So you need more plumbing and chambers, and any backpack superheater is implausibly small.
• You're going to run through any carriable amount of fuel terribly quickly, if you're burning it fast enough for superheating. However, a thermo-electric powered fan will not have enough power to get air through the fire quickly enough for that. Using a small steam engine to blow the fire would work better.
• Corrosion. Very hot water under high pressure is horribly corrosive stuff, unless the water is really clean, as in distilled. Maybe distilled twice, in a post-apocalyptic setting. Classic steam locomotives didn't use very high pressure or temperature. Being next to a bursting boiler was deadly because there was enough steam to scald your whole body, plus flying chunks of metal, not because of high temperatures.

[Green-Neck]

Thanks everyone for your replies.
The proposed weapon is certainly cinematic and not realistic.

I'm not trying to convince people that it's realistic, I'm just trying to explore the functioning of the thing, and then making a 'more realisic' version of a fantasy item.

The proposal was for a backpack with a rocket stove style heater incorporated,burning 1KG coal or wood to heat a10 litre tank of water (with a pressure release valve) to 90 degrees C. A seperate 1 litre tank is heated by accelerating the fire with a TEG powered fan to 250C/ 600 psi just prior to combat. This is released through a wand with a waterjet cutting tip to collminate the stream.

Small non-fan assisted rocket stove can acheive a exhause temperature of 1000C or higher. The fan is to increase heat more quickly during use.

I never realised how dangerous superheated steam was until i talked to a retired worker from a 650psi turbine coal power plant. He said if you heard a high pitch shrill noise, the workers would take their pants off and walk slowlytowards the exit swinging thier pants around. if the pant got cut in half you found the leak. That was 1970's Austrlain health and safty for you.

600psi steam was piped around battleships during ww2 and leaks were detected by waving a broom around until it was cut in half by the invisible pin-hole steam leak.

The materials to contain 600 psi are non-problemic, ie tanks and hoses are common in our society, and a tour of an industrial estate will provide tanks to 3000 psi and hoses to 60,000.

1kg of coal contains 7000 kcal, 1L of water takes 250 kcal to heat. that means the sytem is about 35% efficent, which is optimistic but not crazy.

The campaign will feature black powder weapons and laser rifles with highly limited ammunition. I was trying to essentially have a flame thrower, but to fit the game world better with liquid hydrocarbons being too valueable to spray around. From a meta gaming perspective I used 4d based on having 1/3 the rate of fire of a flamethrower, and not wanting to hamstring my PC too much. This is probably too much.

The suggestion tha the weapon should be more based on cutting damage, with a smaller portion of heat damage is probably more realistic.

[Luke Bunyip]

Originally Posted by Green-Neck

Hello fine folks,

My GM is going to run a post apocolyptic game...

For those of you playing along at home, that would be me. Bwahaha...

Originally Posted by Rolando

If you still want something similar to a steam weapon it is may be better as a high pressure hot water weapon. A water pump like those to clean pavement with very hot water and with a lot more pressure, it can cut and burn, maybe 1d burn but hot water stay hot for a while over the target making it very dangerous for exposed skin, and very distracting.

Heat the water, and then apply force with a compressed gas... it would be shorter range than gaseous H20, yes?

[Green-Neck]

[QUOTE=Heat the water, and *then* apply force with a compressed gas... it would be shorter range than gaseous H20, yes?[/QUOTE]

This could be done, but as heat=pressure it would be much simpler to add more heat. Pressure containment is not a constraint.

[Luke Bunyip]

Originally Posted by Green-Neck

This could be done, but as heat=pressure it would be much simpler to add more heat. Pressure containment is not a constraint.

But if we're talking droplets vs gas, surely range and/or spread and efficaciousness would be affected.

For those of you playing along at home (still), please pitch in.

[Fred Brackin]

Originally Posted by Luke Bunyip

For those of you playing along at home (still), please pitch in.

Sorry, I'm with the "this would never work in relity" group. Which leads to "whatever the gM will allow".

WeeI that gM I would give this the sort of range and damage seen in the Steam Jet spell from Magic. That would all be non-incendiry Burning too. The superpressure cutting efect has a range of less than 1 hex (inches really) even if you could achieve those pressures.

[Rolando]

Originally Posted by Luke Bunyip

For those of you playing along at home, that would be me. Bwahaha...




Heat the water, and then apply force with a compressed gas... it would be shorter range than gaseous H20, yes?

Yes, a "very hot water sprayer" will be plausible and shot range, but plausible.

Otherwise I'm also in the "whatever the GM allows" camp.

If making a steampunk steam thrower is cool and makes everyone happy and fit the game world your group are creating it is the way to go. Just make damage and range go in line with the other common or not so common weapons. But, as always, the GM have the final word about the weapon and it's capabilities, as it is the GM the one that will have to deal with everything this bit of cinematic equipment will affect.

[Luke Bunyip]

Originally Posted by Rolando

... as it is the GM the one that will have to deal with everything this bit of cinematic equipment will affect.

As the GM in question, I tried offering his PC a laser rifle with a pair of dodgy battery packs. This was his counter offer.