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Ancient steam boats:

Vitruvius managed to tame the power of the aeolipyle by connecting its rotation axis to a clock like mechanism. Soon, larger models were created, reaching 10kW sizes. Those were soon connected to series of pulleys in order to increase torque and connected to rowing mechanisms on ships, allowing ships to dispense with oarsmen.

Eolipila, Steam engine Hero of Alexandria
Aeolipyla doing work

The working principle is incredible simple.

By the late 3rd century AD, all essential elements for constructing a steam engine were known by Roman engineers: steam power (in Hero's aeolipile), the crank and connecting rod mechanism (in the Hierapolis sawmill), the cylinder and piston (in metal force pumps), non-return valves (in water pumps) and gearing (in water mills and clocks) Roman technology

Question:

What would be the consequences, for Rome, of a fleet of steam powered boats, both militarily and economically?

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  • $\begingroup$ I am assuming these are wooden....or are they made out of metal? $\endgroup$ – JDSweetBeat Mar 24 '15 at 15:51
  • $\begingroup$ metal, bronze i suppose, but you can see that they can do work, its not impossibe to make this in Rome. $\endgroup$ – Jorge Aldo Mar 24 '15 at 15:59
  • $\begingroup$ it more matters as to why they did this. I mean, in reality they had the knowledge, but chose not to use it because the systems already in place worked so well. $\endgroup$ – JDSweetBeat Mar 24 '15 at 16:16
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It would be as a gateway, plus perhaps some short range transportation. It could be useful in running messages in battle, or possibly in certain river transportation for the uber-wealthy. Beyond that it has few applicable benefits.

That said, technology usually doesn't stay in one place for too long, and building off of that, it's plausible that one could have a working better steam engine in a century or two, which makes a massive difference on many levels.

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The effect of a steam engine of the type described would be minimal. An aeolipile is a very inefficient reaction engine, relying on the mass of the ejected steam to do work, rather than the change in pressure as in more efficient engines.

Given its inefficiencies, it would be good only for short bursts with a relatively long lead time. Such engines could not power merchant shipping for sufficiently long periods, and while they may be of use in military shipping to provide bursts of speed, their long heat-up time would mean that this would only be of limited utility, and in the mean time, the ship is filled with useless running gear that displaces volume that could be packed with personnel, munitions or cargo.

The aeolipile is really only of use as a proof of concept that may lead to more efficient steam engines.

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  • $\begingroup$ Well, reaction turbines are still used today, and, apart from the fact that they discharge inside a closed cylinder that leads to the condenser (causing a lower than 1 atm pressure at this side) a reaction turbine will still use the mass of steam being delivered at high speed to gain speed. Its a reaction turbine afterall... $\endgroup$ – Jorge Aldo Mar 24 '15 at 0:22
  • $\begingroup$ @JorgeAldo, I agree, however a steam turbine recovers its reaction mass via the condenser you mentioned. An aeolipile vents its reaction mass to the atmosphere, making it very inefficient. $\endgroup$ – Monty Wild Mar 24 '15 at 0:25
  • $\begingroup$ @JorgeAldo, the big advantage a reaction turbine has is the shape of the blades -- something the Romans wouldn't be able to figure out, or manufacture if they could figure it out. Without the correct blade shape, a reaction turbine isn't much better than a simple aeolipyle. $\endgroup$ – Mark Mar 24 '15 at 4:25
  • $\begingroup$ I agree that figuring out the format of the turbines (numbers etc) for a impulse turbine would be way beyond roman technology and knowledge. I myself cannot design one. But, a reaction turbine a la aeolipyle is different. Its possible to design a reaction turbine in the manner of aeolipyle to do usefull work by trial and error. This kind of turbine was used to work with steam. $\endgroup$ – Jorge Aldo Mar 24 '15 at 4:29
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The key factor that allows steam engines to change society isn't engine technology - it's fuel availability.

A steam engine - even an efficient one - is merely a toy unless you have significant quantities of cheap, compact fuel... which means fossil fuels (most likely coal). A steam engine big enough to do anything useful takes a lot of fuel, and wood is relatively bulky compared to its energy output. You'd need very large woodpiles to keep the engines stoked (especially if you're running something as inefficient as an aeolipile). It's debatable whether you could carry enough to run the ship at all, let alone do so while also carrying a significant cargo.

It might entertain the nobility to watch a steam-powered boat buzz around the lake for a while, but when you want to actually do anything practical they'd use sails or muscle-power - because they're cheaper and more efficient than trying to find some way to run a large aeolipile off wood and still have room in the ship to do anything else.

Metallurgy is another choke-point - most modern turbine designs would be impossible to build from bronze. Given sufficient quantities of fuel, they could certainly construct some kind of steam engine, but it would be relatively inefficient.

For commercial purposes, wind is probably better, simply because it's free and doesn't cut into your profit margins. Steam power would allow ships to sail into the wind (almost) as fast as sailing with it, which is a major military advantage, but oars can do the same thing. Unless it's powerful enough to outrun a trireme, it's not going to be a big deal there either.

Give the Romans steel and coal mines, and they'd reproduce the Industrial Revolution. Without those, steam engines aren't going to do much of significance.

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  • $\begingroup$ they had coal but not much use for it : The Romans worked almost all the coalfields of England that outcropped on the surface, by the end of the 2nd century (Smith 1997; 323). But there is no evidence that this exploitation was on any scale. After c. 200 AD the commercial heart of the Empire was in Africa and the East where the climate severely limited timber growth. There was no large coalfield on the edge of the Mediterranean. $\endgroup$ – Jorge Aldo Mar 25 '15 at 14:15
  • $\begingroup$ @JorgeAldo the operative words are significant quantities of cheap fuel. Surface coalmines in Britain wouldn't have met either of those criteria for Rome: they had coal, just not enough of it. $\endgroup$ – Toby Y. Mar 25 '15 at 21:53
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You made this relatively easy to answer as you only had 1 question :)

What would be the consequences, for Rome, of a fleet of steam powered boats, both militarily and economically?

Well, the Roman fleet (and every other naval fleet) was comprised of biremes, triremes, quadriremes, quinqueremes. These ships relied mainly on oars for power. A steam ship can go faster and reach its destination sooner than its oar-driven counterpart. The Roman fleet could intercept pirate ships that use oar-craft days before the pirates thought that they would face Rome.

I can also see this leading to a massive innovation in ship technology such as innovating these ships to use large steam guns that can possibly be turned into a steam cannon. This would give Roman ships an impossible to beat edge in ocean battles as it gives them far superior range.

They might even cross the Atlantic—now wouldn't that make for an interesting story.

The economic advantages would primarily be the control of all major shipping routes, but as you can see in history they managed that without steam ships.

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