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 02-06-2014, 04:20 PM #11 Anthony   Join Date: Feb 2005 Location: Berkeley, CA Re: Steam Bomb Your basic problem here is that your container will rupture long before you achieve any useful level of damage, unless the containers are very large. Sure, a steam boiler explosion is dangerous, but that's because it's huge. If we consider a 1m sphere with 10mm thick walls, it has an external volume of 0.52 cubic meters and an internal volume of 0.27 cubic meters; the shell has a volume of 0.25 cubic meters and a weight of just under 1 ton, and it can hold about a quarter ton of water. The shell has a cross-section of 0.28 m^2, the inner cross-section is 0.5m^2. If we assume steel with a yield strength of 400 MPa, that means it will rupture at 224 MPa internal pressure (this assumes no weak spots, which is unlikely) and the total energy contained as pressure is 90 megajoules. If we took the same design and filled it with TNT, it would detonate with an energy of 1,700 megajoules. Black powder would be maybe half that, and might not produce as efficient an explosion, but would still be vastly more powerful than the steam bomb. __________________ My GURPS site and Blog.
 02-06-2014, 04:30 PM #12 Anaraxes   Join Date: Sep 2007 Re: Steam Bomb Let's say the bomb holds ten liters of water. That's 25,959 kJ of energy to vaporize. But the mage only has to heat enemy brains from 37 to 44 C to be nearly certain of death. That's about 1400g * 7 C * 4.186 J/g C = 41 kJ per person, or 633 casualties for the same effort as one bomb. "I can kill you with my brain" is much more threatening than "I can make a pressure cooker explode with my brain". Better yet, a S&W .40 bullet carries as much as 680 J, depending on the load. Not a "kilo" to be seen. The mage is probably better off popping 38,175 people with the equivalent of an S&W .40 round than he is heating up that pressure cooker. The steam bomb is an inefficient way to hurt the enemy army. Magic and physics don't mix well. Mages that can heat a cup of tea with a wave of their hand command surprisingly lethal amounts of energy. You probably don't really want to have magical effects be just another branch of modern physics.
02-06-2014, 04:38 PM   #13
Anthony

Join Date: Feb 2005
Location: Berkeley, CA
Re: Steam Bomb

Quote:
 Originally Posted by Anaraxes Let's say the bomb holds ten liters of water. That's 25,959 kJ of energy to vaporize. But the mage only has to heat enemy brains from 37 to 44 C to be nearly certain of death. That's about 1400g * 7 C * 4.186 J/g C = 41 kJ per person, or 633 casualties for the same effort as one bomb. "I can kill you with my brain" is much more threatening than "I can make a pressure cooker explode with my brain".
Though if you apply enough heat fast enough, you can kill the people next to your target as well. "I can make your brain explode, with such violence that it kills everyone in a ten foot radius" is a pretty decent threat.

The usual constraint on this, whether magical or otherwise, has to do with the difficulty of actually applying the energy where you want it to go. Lots of energy-inefficient methods of killing are still used because it happens to be easier to deliver the energy that way.
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02-06-2014, 04:43 PM   #14
RyanW

Join Date: Sep 2004
Location: Southeast NC
Re: Steam Bomb

Quote:
 Originally Posted by johndallman A pressure cooker explosion is not much like a grenade explosion. The lid of the cooker yields and comes off, releasing the pressure. You don't get the shattering effect of an explosive, so you don't get lots of small fragments moving at high speed, which are what do the damage of a grenade.
As xkcd told it, it isn't usually much more than opening a shaken up can of soda. Well, opening a can of soda hot enough to cause severe burns.
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 02-06-2014, 05:25 PM #15 Gedrin   Join Date: Jul 2007 Re: Steam Bomb The problems I have with BP and TNT is lack of access. I don't have them IMC at the moment. Certainly, they'd be superior explosives. If I could get them rapid firing weapons like the .40 you describe, BP or similar explosives, they'd be better. I'm not sure how to rig that with the available materials. The explosive effect is nice, but I'm not sure shrapnel and concussion would be the biggest impact, but rather the steam. Certainly it would be more intimidating to field brain friers, but I'm having trouble keeping them alive at the ranges effective for a guy with IQ 10 and Magery 0. More capable mages are terrors in combat, but there aren't enough of them. The available materials for battle mages are being used. I've got a decent pool of helpers and the guys who get work because they can power a continual light wand. If there's a better way to take advantage of this material in the field, I'm open to it. If it's a matter of needing to vaporize more water, I can look for a solution to that problem. I'm not worried about magic Energy costs, as the spell defines it to 20-60 degrees per minute for the entire sphere at a cost of 2-6 energy. Given that peacetime resources could be used to produce uniform weapons, and you'd only need to push them to critical, it seems like a decent deal. How much water would I really need at what temp to generate a scalding cloud fourty feet across? That's good enough to disrupt a tightly packed infantry formation.
02-06-2014, 06:00 PM   #16
Anthony

Join Date: Feb 2005
Location: Berkeley, CA
Re: Steam Bomb

Quote:
 Originally Posted by Gedrin How much water would I really need at what temp to generate a scalding cloud fourty feet across?
Depends on the shape of the steam cloud, but on the order of half a ton at boiling temperature.
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 02-06-2014, 06:19 PM #17 Gedrin   Join Date: Jul 2007 Re: Steam Bomb Ran some numbers for heating a sphere to 200C and letting it go. My maths might be off. It's been a while since I did this. 8.3144 * 473 / 101325 = 0.0388 18 / 0.0388 = 463.91 1000000 / 463.91 = 2155.59 Water to steam volume ratio at 200 degrees C, one atmosphere = 1 to 2155 1 KG of water (0.001 m^3) generates 2 cubic meters of steam spherically 200 KG of water (rough max throw of my model RL trebuchet) will generate a sphere of steam about 4.6 meters radius. On the ground this is about 6 ish meters radius(rough). A 12 meter circle of bad is pretty close to my concept target of 14 meters.
02-06-2014, 06:20 PM   #18
scc

Join Date: Mar 2013
Re: Steam Bomb

Quote:
 Originally Posted by Turhan's Bey Company Invented kinda late TL4 (circa 1680, IIRC, which is significantly closer to 1730 than to 1450), and not, to the best of my knowledge, mass produced until the middle of the 19th century. On the other hand, the problem with early pressure cookers was that they exploded messily, which is exactly what you want here. That said, I agree with what has been said about needing a Heat variant that pumps a lot more heat into your water in much less time in order to get a useful explosion happening. You might get more mileage out of adapting the steam cannon from Fantasy-Tech, using a team of magicians with Heat to crank up the temperature of some sort of heating element which then gets water pumped in for the steam-flash propulsion.
Remember that pressure cooker alter the boiling point of water, also this is probably going to be designed like a grenade, made to come apart

 02-06-2014, 07:49 PM #19 Fred Brackin   Join Date: Aug 2007 Re: Steam Bomb You know, Gurps Magic has an index of spells and there's a spell called "Boil Water" in it. It even has Heat as a direct prereq (along with a short chain of basic Water spells). That spell does take 10 seconds to cast but changes the water to pressurized steam instantly when it takes effect. The danger of this is noted in the rules text. Don't be sidetracked by "Create Steam". That doesn't produce pressurized steam. No, you don't want to go to the trouble of inventing a "Fast Heat" spell. It would have to cost an enormous amount of energy to be balanced. __________________ Fred Brackin
02-06-2014, 11:26 PM   #20
Gedrin

Join Date: Jul 2007
Re: Steam Bomb

Quote:
 No, you don't want to go to the trouble of inventing a "Fast Heat" spell. It would have to cost an enormous amount of energy to be balanced.
After a bit of looking, that's what I figured. Given a proper shape, the integrity of the vessel would be sufficient for launch, but fail on impact. Boil Water has additional prereqs, but is the better choice. I'm not sure it's worth doubling the training program's time. Also, not sure you could boil it inside a sealed container.

However, if I know the failure thresholds, a "Test Integrity" spell might be even better. Spell functions similarly to Test Load, but gauges the amount of additional stress before failure. The bombs are heated to the point they can be launched, but will fail on impact. The training program would be quicker, with just Measurement as the prereq. As a bonus, the artillery crew has someone with Measurement.

You'd need some means of monitoring temperature to get in the ballpark or there would be too many accidents. Even if that was expensive, in mundane terms, it would be worth it to cut the required training time down and get Measurement distributed into an artillery corps. Heck, if the specs are tight enough, and they could be with magical manufacture, you might be able to simply use Measurement if you know the proper temperature window.

It might be that the Measurement method would be a "second generation" of the weapons, after those tolerances, shapes and hazards are better understood. Then again, they might invent BP by that point and training to Fireproof would become the need.

Last edited by Gedrin; 02-06-2014 at 11:40 PM.

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