This is the Falkirk Wheel, and it's one of the greatest bits of modern industrial design
in the world.
On the top of that hill is the Union Canal, and down here is the Forth and Clyde Canal.
And the traditional way to get boats between them was a flight of locks, which'd take about
a day to get through, and besides, they were dismantled here in the 1930s. The solution:
the world's only rotating boat lift.
Now boat lifts aren't a new thing. They've been around for centuries. Most of them, like
this, have two caissons, which is the technical term for the tubs that the boats sit in, although
usually they're next to each other rather than rotating round a central point. And the
reason for two is this: to lift 500 tonnes of water 24 metres up, you need a minimum
of 32 kilowatt-hours of power. That's about what an average British house uses in three
days, or an average American house in one day. And that's before friction, that's just
the potential energy you need to put into the system to raise it up that far. But: if
you're also having the same weight of water descend at the same rate, at the same time,
then you're not adding any potential energy at all. On average, nothing is going up or
down. You're just getting a really heavy thing moving, and then stopping it again. Because
of that, this wheel only needs one and a half kilowatt-hours for one lift: less than a twentieth
of what it'd need otherwise.
There are even some boat lifts in the world powered entirely by gravity, where local conditions
and the architecture permit it: you just fill the top one with a bit more water, let it
go, and then apply the brakes when you need to. Bit tricky with something that's as fancy
as this though. It has to be massively reinforced, there is an incredible amount of momentum
there.
And here's the really clever bit: remember Archimedes' principle, the Greek bloke with
the bathtub. A floating object displaces an amount of water equal to its weight. An object
that sinks, sure, that displaces equal to volume, but a floating object like a boat
displaces water equal to its weight. When they're full of water, those caissons weigh
about 500 tonnes. You add ten tons of floating boat into one of them, then ten tons of water
flows out into the canal.
Which means this is balanced no matter how much is actually floating in it.
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