Wheel meet again

The Falkirk wheel is the fascinating centre-piece of a millennium initiative to reopen much of Scotland’s canal network

While the dust settles inside London’s doomed dome, a project which is the dome’s antithesis is nearing completion.

At a cost of around £17 million (the dome cost £750 Million) and with an expected lifetime of 120 years, the Falkirk wheel is the fascinating centre-piece of a millennium initiative to reopen much of Scotland’s canal network.

The wheel will join the Forth & Clyde and Union canals by scooping boats from one canal, lifting them 115 feet in the air, conveying them along a 100 metre long aqueduct and lowering them into the other.

Believed to be the world’s first rotating boat lift, the wheel’s appearance echoes the shape of a double-headed Celtic axe. Its two axe-shaped arms rotate in a continuous circle, 180° at a time, simultaneously lifting and lowering two 22 metre long caissons (watertight containers). These caissons each hold around 300 tonnes (including water and up to four boats). A series of synchronous gears hold the caissons in a horizontal position.

To support the wheel, bearing specialist SKF developed a solution which uses a pair of four metre diameter, three row, slewing bearings, one positioned at either end of the wheel, with outer rings bolted to the support structure and inner rings bolted to the arms. The inner ring of one of the bearings is equipped with gear teeth to transmit the drive to the wheel.

These bearings were designed to be positioned on a horizontal axis and to cope with the specified combination of radial and axial loads. When the wheel is fully loaded, it weighs 1800 tonnes, which results in a radial load of 9095 K Newtons per bearing. Each slewing bearing has three rows of cylindrical rollers, one for the radial load and two with smaller rollers for the axial loads.

The wheel is rotated by ten hydraulically driven gearboxes, via the geared slewing bearing. It turns at a rate of around 0.125rpm, which sees it lift and lower boats at an average rate of 4 metres per minute.

The wheel’s designers believe that in operation it will be maintained close to perfect balance thanks to a pump system, which will equalise the water levels in the two caissons.

As well as serving a practical purpose by rejoining the canal link between Glasgow and Edinburgh, the wheel is also expected to draw in huge numbers of visitors when it is completed at the end of this year.