The hermetic waterwheel

I have been thinking about a hermetic waterwheel. The reason I have been thinking about this is because the waterwheel is the dominant form of power that is not muscle based in medieval Europe and by the 13th century was becoming widespread.

So I started to think about how to make one for a covenant, and came up with this:

Make a 5m diameter waterwheel, which is large but not unimaginable large in the period. At the top of it, put an approximately 4 meters in a side cube, made of some waterproof material. This is again very large, but not unusual at all. Dig a lake under it.

The enchant an item that produces water using craq guideline of 2, touch range, diameter duration, unlimited uses. Level 14, you could power up by a factor of 10 for only one more level.

The individual for aquam is a body of water of about that volume. If you want to go level 15, you can make it 10 times bigger.

Power works out at about 100kw (roughly 135hp) That is a lot, but again it is an amount that is only double what the forge mills in France and England were using at the time.

This would be incredible for mining on covenant ground as it could haul all the rock and the water would not flood the mine as it disappears.

You could use it for drop forged as the French and English are doing at the time, for massively helping iron production.

1203 has a tool sharpening mill in France, and tanning and fulling mills are fully a hundred years old.

The key thing here is how simple the enchantment is. What other enchantments are also

a) in period (industries were massively improving water power use in 1220)


B) cheap and efficient


Not that manpower is terribly expensive, compared to Vis, but you'd probably want to add an automated trigger (when vessel is empty) to automatically recast the CrAq. Last thing you want is for the wheel to stop at a key moment, because the Homer the button pusher got distracted/fell asleep.


On the other hand, the not-perpetual wheel might be a safety feature, so that if Homer the button pusher hears bones breaking and screaming in the mines, it doesn't just keep going wrong (for too long).


That makes sense for me. Makes a nice easy job for someone injured in the covenant's service to retire to as well.

For 2 more magnitudes and thus the same pawna of Vis you could move target to group and range to voice and then you could make 10 mills work....


Check out "the hermetic generans" in TME p.125: basically, use ReTe to make a (1hp) metal disk spin endlessly.

I'd note that the design in TME is vastly inefficient -- you do not need an enchanted device, nor do you need metal. A (probably non-fatiguing) spontaneous spell should suffice on a (Ring surrounding a) wheel of clay: Base ReTe 2 (as per TME, though I'd argue that keeping a wheel spinning woud probably qualify for ReTe 1), +1 R:Touch, +2 D: Ring. +0 T:Circle is just ReTe 5. Combine multiple ones for higher power...


But part of why I thought of the wheel is you could bury the resorvoirs and run an aquaduct out of any hill a d pretend to have just found a spring you power the town via.

Learned people might call nonsense, but to many a water wheel coming out of a hillside will be much more acceptable than a endlessly turning sorcerous wheel

Al's the clay wheel uses guidelines which the spells use str 5 people as an outline. A waterwheel can make much, much more

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"The Wheel" in HP p.61 is another example of a self powered wheel, using ReHe. They even talk about having a horse there as cover.

Windmills were becoming a popular thing in Europe during the 12th century as well. So one of them would be a viable option if you wanted something not so obvious as an endlessly spinning wheel.

Sure, but note that the sorcerous wheel need not be in plain sight (push come to shove, you can always mask it with a D:Ring illusion).

Indeed, by TME it is roughly 1hp (though each magnitude increases that tenfod). However, you can grow that arbitrarily by having arbitrarily many wheels - and note that it takes just one spell to move them all!

the big question is the efficiency of the water wheel, medieval water wheels were quite inefficient so you might not get as much power out of it as the math suggests.

Undershot waterwheels can only achieve an efficiency of 15 to 30 percent. It was know to the Romans but not used much.

The overshot waterwheel, which is what has been described here, has an efficiency of 50 to 70 percent. It is first seen appearing in the fourth century , but was mostly seen appearing in cities at the time. Its use was widely spread in Europle by the Benedictines and it was in wide use by the 10th century.

Reference: Cathedral, Forge, and Waterwheel (Technology and Invention in the Middle Ages), Frances & Joseph Gies, 1994, published by Harper


I am calculating horsepower at 50% efficiency as the book @Arthur mentioned indicated. I may have enjoyed a book on medieval tech too much

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any technology can have a decreased efficiency down to 0%. If the gears are misaligned or any of a thousand other possible problems come up. Overshot water wheels were calculated to have 6% efficiency in the eighteenth century with calculations being done on the most advanced water wheel designs of the era. A 2 meter wheel was the standard for that calculation and larger wheels likely had losses due to system torques in excess of the calculations as well, plus additional weight producing additional system requirements that would likely reduce efficiency further.
I did find reference to an arab built 20m water wheel (I think this was an undershot wheel, not overshot), but fundamentally I believe for large wheels someone will need some kind of engineering ability to check against (artes liberales?)


The technolology is relatively well-known by the time preiod covered by Ars Magica, so a number of Profession abilities probably understand how to build and maintain such wheels. Profession: Miller would certainly cover maintenance and repair of the waterwheel-driven mill. Someone with Profession: Builder would know how to build one adapted to an appropriate location.

Artes Liberales, I think, covers some theorical aspect (geometry), but not the actual building of a waterwheel. It is a useful supporting ability for a builder or architect, but I wouldn't use it for the actual engineering task. YMMV.

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