# The tide sets the shift, and the tide keeps moving

> A tide mill can grind while the ebb runs and not otherwise, and because the ebb starts fifty minutes later each day, the miller's hours walk right around the clock.

August 19, 2026 · https://justog.club/stories/tide-mill-working-nights

A tide mill, drawn in section. Behind the wall a pond, then a sluice gate, then an undershot wheel
turning gearing that climbs to the millstones above it. The water's marked at two heights, HIGH and
LOW, right at the pond's edge.

That's not two moments in the same drawing. It's the two states the whole job depends on, six hours
and a bit apart.

## What's actually printed on this shirt?

A working section through a tide mill, and the two water levels the entire operation turns on.

The cutaway runs pond, sluice, wheel, gearing, millstones — the actual path the water and its power
take through the building, drawn as a diagram rather than a picture of the mill from outside. HIGH
and LOW aren't decoration on the pond wall; they're the two conditions a miller has to track, because
the gate does its useful work in the interval between them and nowhere else in the cycle.

## Why can the wheel turn on the ebb and not the flood, and why does that keep moving later?

Because the pond stores water at high tide, and it's the difference in level, not the tide itself,
that drives the wheel — and that difference shifts by fifty minutes every day.

At high water the sluice closes and the pond fills level with the sea. As the tide drops outside,
the pond stays full until the miller opens the gate — the head of water between the full pond and
the falling sea pushes the wheel round, and once the two are level again the head is gone and it
stops, whatever the clock says. The flood tide simply refills the pond. Because the tide follows the
moon, that window starts about fifty minutes later each day, so a mill grinding six till noon today
grinds seven till one tomorrow, and inside two weeks the window has walked all the way round the
clock. A tide miller doesn't pick a pattern the way [a nurse's rota gets
set](/stories/nurse-shift-shirt) — the tide sets it, and nobody's asked.

## What makes a good print of a tide mill, rather than a pretty building exterior?

Showing the mechanism the tide actually drives, not the building it happens to sit inside.

A mill drawn from outside is a picture of a shed by a pond; a mill drawn in section, with the
water's path traced through sluice, wheel and gearing up to the stones, is a picture of how the tide
becomes flour. The two water levels marked HIGH and LOW do more work in this print than any amount
of weatherboarding or a chimney would.

## Can I put a real mill's name or a real millwright's mark on this?

Yes, with the mill's or the maker's permission — the cutaway itself, the pond-sluice-wheel-gearing
layout, belongs to nobody.

A section through a tide mill describes how the type works, the same as any technical drawing of a
widely used structure, and it's free to draw. A specific mill's name over the door, or a specific
millwright's stamp on the stones, identifies a real business or a real historic site, and using
either is a permission worth having if that particular mill is genuinely the point.

## Does the tide-driven cutaway work for a job set by something other than the sea?

Yes — anything whose hours come from a cycle outside anyone's control tells a similar story.

[A farm's working day follows season and weather rather than a rota](/stories/farm-shirt), and
[a weather station logs whatever conditions arrive, on no schedule it gets any say in](/stories/weather-station-observation)
— different mechanisms, the same shape of job: a natural cycle decides the hours, and the worker
fits around it rather than the other way round.

## Isn't a cutaway diagram too technical to actually want on a shirt?

No — the two water levels and the path between them read at a glance, without any engineering
behind them.

The drawing doesn't ask anyone to understand how a mill works before it lands: HIGH sits above LOW
at the same wall, a wheel sits between a gate and a set of stones, and the shape alone tells you
water goes in one end and power comes out the other. Knowing exactly why the ebb does the work and
the flood doesn't is a layer underneath that, not a condition for the print to read.

## Does it print well?

Yes — a single cream ink on slate holds a technical line drawing better than colour would.

Cutaway diagrams live or die on clean, consistent line weight, and one ink keeps every part of the
mechanism — sluice, wheel, gearing, stones — at the same visual weight rather than letting colour
pick a favourite. HIGH and LOW stay plain lettering at the pond wall, not a banner or a badge, which
keeps the whole print reading as a working drawing rather than a poster about one.

## How do I get one made?

Describe your own mill, or the mechanism behind whatever your hours actually run on, at
[JustOG](/) — pond, sluice, gearing, the two levels that matter.
Pick a direction, drag the crop frame, see it composited on the real garment, and it's made to
order and shipped.

Designs other people have published are in the [shop](/shop).

HIGH at the wall, LOW at the wall, and a wheel that turns for the hours between and not otherwise.