Horizontal waterwheels were invented at least 2,000 years ago. They allow the force of the water to spin a mill without the use of gears. Horizontal waterwheels ran medieval grist mills in Ireland for at least 500 years.
My model was inspired by the Nendrum Monastery archeological site in northern Ireland.
During the early 7th century (circa AD 619), the monks walled off a small inlet on Strangford Lough, and built a tidal mill. They opened gates as the tide came in, filled the pond and closed the gates. At low tide, they released the water through a penstock that turned the horizontal waterwheel. The waterwheel was attached to a shaft which led up to and turned a millstone to grind their grist (unprocessed grain).
The extant paddles and granite millstones are from the AD 787 refit of the mill.
Most waterwheels are situated in streams, which have a steady flow, rather than the cyclical current from the tides.
I researched tidal mills after taking Master MacThoy's virtual class, "The 12th Century Industrial Revolution".
The Nendrum paddles were carved from local oak. I used basswood to make the carving easier. My lighter wood also reduced the model's weight, allowing it to spin more easily. Working waterwheels needed the strongest available wood since they were turning millstones weighing hundreds of pounds.
For the millstones, I substituted maple. The Nendrum stones were granite. The best stone for mills is limestone or marble since calcium carbonate is better to eat then sand.
The millstone are not proportional. The Nendrum stones are similar in size to the waterwheel. Since mine is a model, I reduced the weight by reducing the stones' diameter.
I carved the paddles by hand using small, modern carving tools. For the maple millstones and hub, I used the scroll saw and drill press.
The most-important, least-period piece turned out to be the Kevlar safety gloves.
Carving has intrigued me for a while. I started carving the first paddle early in quarantine as a way to learn the techniques. It took several months, and several successful paddles, to gain the courage to create the working model. This is my first attempt at hand carving. All the little animals I made for largess were cut on the scroll saw. The last couple paddles are much smoother and more consistent than the first few.
I wouldn't remake this until I had the skill to carve identical paddles. The hub would be much easier to assemble if the tabs were a more consistent size and shape. The original probably had two dozen paddles, and they stacked against each other to provide additional strength.
The most complicated part of this project was attaching the running stone to the shaft. The stone rests on an x-shaped bearing. The bearing must support the full weight of the stone, yet allow for adjustments for different grain sizes, and be removable when the stone needs dressing (carving lines in the grinding surface). The bearing could be attached with shims, wedges, pegs, nails, or even be carved directly into the shaft. I used a strip of linen to achieve the tight fit. I would continue to research bearing attachments, and experiment more, especially if I used an actual (heavy) stone.
The bedstone must stay in place. Woodbutter along the shaft reduced friction enough to keep it stable. For a working mill, the weight of the stone sitting directly on the floor of the mill would provide stability.
MacThoy, Killian Flynn. “12th Century Industrial Revolution by Master Killian Flynn MacThoy”
Gies, Frances and Joseph. Cathedral, Forge, and Waterwheel. Technology and Invention in the Middle Ages. HarperCollins, New York. 1994.
“Harnessing the tides: Excavating the earliest mills in Ireland”
“Nendrum Monastic Site – The Stone Carving Collection and Visitor Centre”
Rynne, Colin. “The Technical Development of the Horizontal Water-Wheel in the First Millennium ad”
“Tide Mill at Nendrum”
“The World’s Earliest Dated Tide Mill” (YouTube video)
Multiple random YouTube videos on carving techniques.
Thank you to Piero Della Casa for building the frame for the model, and for hours of technical discussions.