'Rotating lock' lifts boats, links waterways

DN Staff

May 20, 2002

3 Min Read
'Rotating lock' lifts boats, links waterways

Site clearance for the Falkirk Wheel began in early 2000, construction started in April that year, and the wheel made its first revolution in December 2001. Testing is underway with a ceremonial opening HM the Queen scheduled for May 2002.

Falkirk, Scotland-Imagine a Ferris wheel with two gondolas. Picture the gondolas as water-filled boxes that move around a central axis like a two-chambered revolver. Together, these two images describe a radical new boat lock called the "Falkirk Wheel."

More than two centuries ago, the east and west of Scotland were linked by the Forth and Clyde Canal. Later, the Union Canal was built to provide a connection to Edinburgh, Scotland's capital. The two canals met near here, but with a 35m difference in water levels, a flight of locks was needed to connect them. The canals fell into disuse a generation ago. Renewed as one of the British government's "Millennium Projects," the link between the canals is now being restored with the Falkirk Wheel replacing the original 11 locks.

Falkirk Wheel bearing/gear arrangement

The result is one of the most innovative engineering projects of the decade. The Falkirk Wheel's two gondolas each measure 22m long, and mount on wheels within steel rings supported by opposing arms 35m long. The arms rotate about a 3.8m diameter axle to carry the gondolas 180 degrees between the higher and lower levels. Each gondola accommodates a 4-boat, 300-ton payload, including the water.

At the lower level, the gondolas are suspended within a concrete caisson. A telescoping frame clamps a watertight seal between caisson and gondola, and the boats sail in or out. "The undersides of the gondolas are always dry," notes Project Manager Paul Hudson of Butterley Engineering, the structural engineering firm responsible for design and construction of the Falkirk Wheel. At the upper level, the gondolas are aligned with the aqueduct into or from which the boats sail.

Hudson adds that the amount of water in each gondola depends on water level in the basin to which it is open, and the number of boats carried makes no difference as the vessels simply displace a volume of water of equal mass. After the doors are closed, he says, a pump system equalizes the water levels between gondolas to balance the weight.

A series of cogs and gears, positioned between the steel rings and the axle, ensure the gondola stays level throughout its traverse. Because the wheel assembly weighs 1,800 tons, a massive slewing bearing supports the axis at each end. Bearings like these are normally used in large dock cranes or excavators where there are extremely heavy axial loads. Each bearing measures 4m across, with outer rings bolted to the support structure and inner rings bolted to the arms.

The driveline to the wheel is taken through one of the inner bearing rings that is fitted with transmission gear teeth. Ten hydraulic gearboxes rotate the wheel at one-eighth revolution/minute. This means ascent or descent can be done in about 7 minutes. With allowance for entering and leaving the gondola, about four loads/hour can be handled in each direction.

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