If someone in the 14-15th century world had the knowledge required to build an engine for use in locomotives and ships, what kind of engine could be made using technology that already existed back then?

  • $\begingroup$ I edited your question to make it more direct and added some tags. I will say that, while adding an engine to a ship could be a great invention in the right circumstances, building a locomotive makes no sense in a world without train tracks. Maybe you meant something more general instead of "a powered rail vehicle used for pulling trains"? A land vehicle? An electric carriage? $\endgroup$ – Cyn Feb 2 at 20:50

Steam engines

Edward Somerset had a patent for one in the 1600's and Thomas Savery (1650–1715) was the inventor of the first commercially used one, which is only 100–200 years past your time frame.

But the first recorded steam engine was as early as the 1st century Egypt so the principles were known 1500–1600 years before your time-frame which means it's far from a great stretch for you to say development of steam engines that entered common usage was a little earlier in your world.

The propeller didn't come along for a while longer than that of course but paddle steamers are simply a reverse water wheel (which the Romans had) and Archimedes' screw also existed then, so that gives you two potential methods of transferring power from the engine to propel your ships.

Paddle steamers are your most likely ships, especially as the Romans already had ox powered paddle boats (there's a reference to them in the link).

A simple vertical single cylinder engine used to drive a wheel or paddle is probably most likely.

Though this horizontal design is a touch more elegant to my eye.

inserted elegant design!

They'd probably be wood burning rather than coal.

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    $\begingroup$ Referencing the aelopile is misleading. Until you can develop much better materials, it's a dead end. And the working principles used are not easily applied to other approaches. $\endgroup$ – WhatRoughBeast Feb 2 at 19:42
  • $\begingroup$ +1, but note that "the 14-15th century world" means the period from 1301 to 1500 (and presumably closer to the center of that range than the edges). So some of your figures (describing 1698 as "only 100–200 years past your time frame" and the first century CE as "1500–1600 years before your time-frame") seem a bit off. $\endgroup$ – ruakh Feb 2 at 21:11
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    $\begingroup$ Note that Somerset's/Savery's engine isn't a steam engine as we think of it. It's a steam pump, using steam acting directly on water to move the water. If you replace the water with a piston, you now need much higher manufacturing tolerances to keep the steam from blowing past the piston. Further, early 1700s' metallurgy was just barely capable of making parts that wouldn't blow up under pressure; I doubt that 1400s metallurgy could do the job. $\endgroup$ – Mark Feb 2 at 21:24
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    $\begingroup$ @Mark a pump capable of moving water is enough for ships. In fact I am actively annoyed about how alternate history fiction insists on building complex steam engines and paddle wheels or propellers when the first step for a ship probably should be a pump working directly on the water. Historically this did not happen because our steam ships are just ships with steam engines developed for another purpose but if you write a story about using "future technology" to build superior warships in a few years... And yet everybody does what our history did but faster. $\endgroup$ – Ville Niemi Feb 3 at 0:10
  • $\begingroup$ @Mark And no, this does not really have anything to do with you or the topic. It just happens to be a pet peeve of mine so I could not resist the temptation. Sorry. $\endgroup$ – Ville Niemi Feb 3 at 0:11

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