The Falkirk wheel is the centrepiece of the Millennium Link, the largest canal restoration project in Britain, designed and operated by British Waterways.
Many moons ago, two canals, the Union canal and the Forth & Clyde Canal connected Edinburgh and Glasgow. These two canals were joined at the town of Falkirk. Over the years the canals lost out to the railways at first and then to road transport, and gradually fell into disuse.
In 1994 the Millennium Link project was set up to restore the 2 canals. The centrepiece of the project, the Falkirk wheel, was unveiled in December 1999. This unique structure, which can only be described as a rotating boat lift, will connect the two canals instead of the series of 11 locks that were used up until the 1930s. As unique as the concept may seem, the idea of a "boat lift" had occurred to a German engineer as early as the start of the 20th century.
Construction of the £17 million structure began in February 2001 and was completed towards the end of 2001. The wheel was due to be opened at the beginning of May 2002, but senseless acts of vandalism delayed this. If all goes well the Falfirk wheel should last around 120 years. Since its opening it has been a popular tourist attraction.
A boat lift !
Here's a crude ascii art representation of the Falkirk wheel seen from the side:
-> to union canal
<- to forth & |===============|
clyde canal | |
and from the front:
| +------------+ |
+ | | +
| +------------+ |
+ | | +
To give you idea of the scale of things, the construction is around 35 m high and 27 m long.
Two large containers, each filled with around 300 cubic metres of water pivot around a central horizontal axis. Boats enter one of the containers from one of the canals, the lift then rotates, so that the two containers swap positions (a system of gears ensures that the containers stay horizontal). The boats can then move onto the other canal. Total journey time: less than 2 minutes (and in case you don't know, that's a damn sight quicker than going through 11 locks).
How it works
At first you might think that lifting several hundred tons of water and boat is going to needs lots of energy, and thus be expensive. Luckily the Falkirk wheel dodges this difficulty: the motors that power it only need around 1.5 kW of electricity, and are almost completely silent. You may be wondering how one can shift all this water around with about the amount of power needed to run 1 or 2 electric kettles. It's really quite easy.
Initially both the 2 containers have around 300 cubic metres of water in them. A boat enters a container. Thanks to our friend Archimedes and his little principle, we know that the boat will displace a volume of water that weighs the same amount as the boat. That water goes back into the canal, which means that the container still weighs exactly the same!
This means that the other container acts as a counterweight: as 300 tons of boats and water are going down on one side, 300 tons of boats and water are going up on the other side. Thus we only need to provide a very small amount of energy, just enough to get the whole structure moving, compensate for friction while it's moving and stop it at the end.
march 2003 issue of Science et Vie Junior