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Could a steam powered cannon be a practical weapon? And if so how good a weapon might it be?

As a measure of how good a steam cannon might be, comsider how might it compare to existing weaponry in terms of range and weight of projectile. For example hand guns, machine guns, small calibre howitzers, 6 inch navel guns and 12 inch naval guns.

I would be interested to know what aspects would limit the abilities of the steam cannon and what might be done to increase its effectiveness.

Consider the technology of 1918 as a base case, but more recent technical innovations might also be of interest if they make a big difference.

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  • $\begingroup$ en.wikipedia.org/wiki/Holman_Projector, en.wikipedia.org/wiki/Steam_cannon, also Mythbusters Episode 55. $\endgroup$ – Eike Pierstorff Oct 22 '17 at 21:34
  • $\begingroup$ In summery: Steam cannons were used and were moderaitely effective but not as effective as an Oerlikon 20 mm cannon. Archimedes would have been unable to build a powerful steam cannon. But what else might be possible? $\endgroup$ – Slarty Oct 22 '17 at 23:18
  • $\begingroup$ Mythbusters did an episode on this. They also looked at a steam driven Gatling gun.It was based on prototypes from the American Civil War. Neither was quite effective. The problem was keeping the steam up under continuous fire, if I remember. Winans steam gun $\endgroup$ – Justin Thyme Oct 23 '17 at 1:22
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    $\begingroup$ Instead of cannons you might want to investigate steam powered catapults. If they can launch fighter aircraft there is at least a chance that they will also launch a viable projectile. $\endgroup$ – Eike Pierstorff Oct 23 '17 at 7:17
  • $\begingroup$ Yes very good idea although I suspect that a steam catapult is just a specialised type of steam cannon. The advantage being the acceleration can be applied much more uniformly over the entire length of the “barrel” whereas a traditional explosive change would be a massive thrust initially that rapidly tailed off. $\endgroup$ – Slarty Oct 23 '17 at 11:56
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For the sake of simplicity, I'm going to compare a regular cannon, to a steam cannon.

A regular cannon uses explosion from gunpowder to push a cannon ball out from the barrel, and a steam cannon uses pressurized steam to push a cannon ball.

one of the main problems is that you will need to use pressurized steam, so you will need to have a tank to store the steam (that also serves as the heater), and a valve to control the flow of it to the barrel of the cannon. Using a regular cannon you just put the gunpowder at the back of the barrel, and that's that; no need for a tank to store steam, and a valve to control it.

another problem is that you will need way more steam than gunpowder (volume wise) to push a cannonball of the same size.

For use in the battlefield, a steam cannon will be very unwieldy; and dangerous to use.

Edit : Looking at the comments, I'm going to add a few more things.

A conventional cannon, has a fuse (optional); the propellant (gunpowder) a barrel, and the projectile (cannon ball). even with only 3 to 4 components; alot could go wrong. Imagine a steam cannon; there's the boiler (which by itself also has a few components of it's own), charcoal/coal to burn, the barrel, a valve to control when to release the steam, and finally the projectile.

When designing a weapon (or anything actually) it is best to keep it as simple as possible; to prevent anything from going wrong (anything that could go wrong WILL go wrong).

in the comments :

One advantage a steam cannon would have would be the size of the gas reservoir could mean that the pressure fall could be much lower as the projectile moved up the barrel

Well, it IS technically correct; but you have to keep in mind the amount of heat, and water you would need for it to work. It would be far more effective to just use gunpowder.

Regarding the power of Steam : Link

Converting BTUs into Joules : Link

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  • $\begingroup$ +1 for ‘dangerous to use’. Pressurised steam will literally strip flesh from bone in an instant. If the cannon misfired your entire gunnery crew could get their skins melted off. $\endgroup$ – Joe Bloggs Oct 23 '17 at 6:27
  • $\begingroup$ @Joe but if cannon explode, crew is usually dead, too. Problem is with the chance of explosion. $\endgroup$ – Mołot Oct 23 '17 at 7:15
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    $\begingroup$ @Molot: even if a valve pops or there’s a bullet hole put in the pressure tank you’ll immediately fill the area with a deadly cloud of water vapour. It’s not just during firing, it’s at every point up to, during and after firing, including the possibility of a cannon turning into an area denial weapon because it’s boiler is still on and it’s spraying scalding hot water everywhere. Steam is not a pleasant thing. $\endgroup$ – Joe Bloggs Oct 23 '17 at 7:23
  • $\begingroup$ The gases generated by an exploding gun cartridge also contain a lot of steam and would be even more deadly than the high pressure steam we are talking about. The advantage with the traditional gun is the high pressure is well contained and exists for a short period, but in a steam cannon the pressure is maintained continuously and externally. One advantage a steam cannon would have would be the size of the gas reservoir could mean that the pressure fall could be much lower as the projectile moved up the barrel, although the initial pressure would be less. $\endgroup$ – Slarty Oct 23 '17 at 9:31
  • $\begingroup$ Safety is a negligible criteria in this. If you spent the same amount of engineering on a steam cannon as you did modern cannons it could be just as safe as a modern cannon. Both systems are machines controlling lethal amounts of kinetic and thermal energy. $\endgroup$ – anon Oct 23 '17 at 15:09
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Compared to modern and emerging weapon tech this is useless.

Building steam requires significant time and energy and extra faculties. Igniting explosive compounds as a propellant takes no time at all.

As for what they can deliver, its virtually the same because both methods are hot gas that is pushing a projectile.

Now compare that to emerging electromagnetic weapons like the railgun. No more costly chemicals or projectiles and far superior speeds. Just a lump of metal flying at insane speeds causing tons of damage.

Note:

The iron triangle in weapons is range, precision, and rate of fire (there is also the destructiveness of its projectile however that is subject to its operational need). Because this significantly hinders RoF it fails as an alternative.

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  • $\begingroup$ A railgun requires a power plant or a very large battery. Explosives are rather more compact. $\endgroup$ – Eike Pierstorff Oct 23 '17 at 15:06
  • $\begingroup$ I want to remove explosives entirely, see my other question worldbuilding.stackexchange.com/questions/95561/… if possible and replace them with something cumbersome that can’t easily be adapted to hand weapons. So you are correct and this is an advantage for my story. $\endgroup$ – Slarty Oct 23 '17 at 15:15
  • $\begingroup$ @Slarty then you don't really need this question, just steam punk it. The steam engine was almost discovered by the ancient Greeks (Herodotus) however gunpowder was barely used in weaponry till the Europeans got a hold of it after the Asians had it for almost 1000 years. Perfectly reasonable to substitute steam for gunpowder in a steam punk world. $\endgroup$ – anon Oct 23 '17 at 15:25
  • $\begingroup$ @anon I may well do that, although I do like to make things as realistic as possible because there's bound to be a need for something odd to be required and I would rather not strain the reader’s credulity any further than was absolutely necessary. $\endgroup$ – Slarty Oct 23 '17 at 15:41
  • $\begingroup$ Well its a strain if you are trying to argue an alternative tech that we intentionally moth balled is some how more effective than a tech we chose. However, history is littered with examples of technologies not realized when they could be and lost. Though, by not discovering gunpowder I feel as though chemistry would ultimately be undiscovered which is great for you because that is how we ultimately make a lot more explosives. $\endgroup$ – anon Oct 23 '17 at 16:05

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