boat lift

Anderton Boat Lift

The Anderton Boat Lift near the village of Anderton, Cheshire, in north-west England provides a vertical link between two navigable waterways: the River Weaver and the Trent and Mersey Canal.

Built in 1875, the boat lift was in use for over 100 years until it was closed due to corrosion in 1983. Restoration started in 2001 and the boat lift was re-opened in 2002. The lift and associated visitor centre and exhibition are operated by British Waterways. It is one of only two working boat lifts in the United Kingdom; the other is Falkirk Wheel in Scotland.

Economic background

Salt has been extracted from the rock salt beds underneath the Cheshire Plain since Roman times. By the end of the 17th century a major salt mining industry had developed around the Cheshire "salt towns" of Northwich, Middlewich, Nantwich and Winsford.

The completion of the River Weaver Navigation in 1734 provided a navigable route for transportation of the salt from Winsford, through Northwich, to Frodsham, where the Weaver joins the Mersey. The opening of the Trent and Mersey Canal in 1777 provided a second transport route, which ran close to the Weaver Navigation for part of its length, but extended further south to the coal mining and pottery industries around Stoke-on-Trent .

Rather than competing with one another, the owners of the two waterways decided that it would be more profitable to work together. In 1793 a basin was excavated on the north bank of the Weaver, at Anderton, which took the river to the foot of the escarpment of the canal, above. Facilities were built for the trans-shipment of goods between the two waterways, including two cranes, two salt chutes and an inclined plane, possibly inspired by the much larger Hay Inclined Plane at Coalport. These facilities were extended with a second quay built in 1801 and the construction of a second entrance to the basin in 1831 .

Planning and design

By 1870 the Anderton Basin was a major interchange for the trans-shipment of goods in both directions, with extensive warehousing, three separate double inclined planes and four salt chutes. However, trans-shipment was time-consuming and expensive, and the Trustees of the Weaver Navigation decided that a link between the two waterways was needed to allow boats to pass directly from one to the other. A flight of canal locks was considered but discarded, mainly because of the lack of a suitable site and the loss of water from the canal that would have resulted from operating locks. In 1870 the Trustees formally proposed a boat lift between the waterways. The Anderton Basin was the obvious site for such a boat lift. The Trustees approached the North Staffordshire Railway Company, then owners of the Trent and Mersey canal, to ask if they would contribute towards the cost of the boat lift. However, this approach was unsuccessful, so the Trustees agreed to fund the boat lift themselves .

The Trustees asked their chief Engineer, Edward Leader Williams, to draw up plans for a boat lift. Leader Williams considered various ideas and finally settled on a design involving a pair of water-filled caissons, which would counter-balance one another, and so require relatively little power to lift boats up and down. A similar boat lift on the Grand Western Canal, completed in 1835, used chains to connect the caissons via an overhead balance wheel. However, this design require a very solid masonry superstructure to support the weight of the loaded caissons. Leader Williams realised that if he used water-filled hydraulic rams to support the caissons instead, then the weight of the caissons would be borne by the rams and their cylinders, buried underground, and a much lighter superstructure could be used. He may also have been inspired by inspecting a hydraulic ship lift and graving dock at the Royal Victoria Dock in London, designed by experienced hydraulic engineer Edwin Clark .

Having decided on a hydraulic ram design, Leader Williams appointed Edwin Clark as principal designer. The Anderton Basin, at that time, consisted of a cut on the north bank of the Weaver surrounding a small central island. It was decided to construct the boat lift itself on this island. The two wrought iron caissons were each long by wide by deep, and could each accommodate two narrowboats or a single barge with a beam of up to . Each caisson had a weight of 90 tons when empty and 252 tons when full of water (because of displacement, the weight is the same with or without boats). Each caisson was supported by a single hydraulic ram consisting of a hollow long cast iron vertical piston with a diameter of , travelling within a buried long cast iron vertical cylinder with a diameter of . At river level the caissons sat in a water-filled sandstone lined chamber. The above ground superstructure consisted of seven hollow cast iron columns which provided guide rails for the caissons and supported an upper working platform, walkways and access staircase. At the upper level the boat lift was connected to the Trent and Mersey canal via a long wrought iron aqueduct, with vertical wrought iron gates at either end .

In normal operation the cylinders of the two hydraulic rams were connected by a diameter pipe, which allowed water to pass between them, thus lowering the heavier caisson and raising the lighter one. To make adjustments at the start and end of a lift either cylinder could be operated independently, powered by an accumulator or pressure vessel at the top of the lift structure, which was in turn kept primed by a steam engine. If necessary, the steam engine and accumulator could operate either hydraulic ram on its own, thus raising the caissons independently, although this would take about 30 minutes to raise a caisson from river level to canal level, as opposed to 3 minutes in normal operation .

Construction

In October 1871, the Trustees of the Weaver Navigation held a Special General Meeting, which resolved

to consider the desirability of constructing a lift with basins and all other requisite works for the interchange of traffic between the River Weaver and the North Staffordshire Canal at Anderton and of applying to Parliament for an Act to authorise the construction of such works ....

In July 1872, Royal Assent was granted for the Weaver Navigation 1872 Act which authorised the construction of the boat lift. The contract for construction of the lift was awarded to Emmerson Murgatroyd & Co. Ltd. of Stockport and Liverpool. Work started before the end of 1872, and took 30 months. The Anderton Boat Lift was formally opened to traffic on July 26, 1875. The total cost of the work was £48,428 .

Problems of hydraulic operation

For its first five years of its life the boat lift operated successfully, with the longest closures being during spells of cold weather when the canal froze over. However, in 1882 one of the cast iron hydraulic cylinders burst while the caisson that it supported was at canal level with a boat in it. The caisson descended rapidly, but fortunately the water escaping from the burst cylinder slowed the rate of descent, and the water-filled dock at the river level softened the impact. No-one was hurt and the superstructure of the lift was not damaged. During subsequent testing, the second cylinder failed too, and the boat lift was closed for six months while sections of both cylinders were replaced and the connecting pipework, which was thought to have contributed to the cylinders' failure, was redesigned .

Volumes of traffic through the lift grew steadily through the 1880s and 1890s, but the hydraulic cylinders continued to give problems. The gland of one cylinder (where the piston travelled through the cylinder wall) had to be temporarily repaired in 1887 and replaced in 1891, and the gland of the other cylinder was replaced in 1894. However, the main cause for concern was corrosion of the pistons. The use of canal water as a working fluid in the hydraulic system, and the immersion of the pistons in the wet dock at river level led to corrosion and "grooving" of the pistons. Attempts to repair these grooves with copper made matters worse, as this reacted electrolytically with the acidic canal water and hastened the corrosion of the surrounding iron. In 1897 the lift was converted to use distilled water as its working fluid. This slowed down the corrosion, but did not stop it completely. Over the next few years maintenance and repairs took place with increasing frequency, each occasion requiring either the complete closure of the lift for several weeks or a period of reduced and slower operation with a single caisson .

Conversion to electrical operation

By 1904 the Trustees faced the imminent prospect of a having to close the boat lift for a very considerable period in order to replace the hydraulic rams. They asked their chief Engineer at the time, Colonel J.A. Saner, to investigate alternative solutions. Saner proposed an innovative solution in which the hydraulic rams would be replaced by electric motors and a system of counterweights and overhead pulleys, allowing the two caissons to operate independently of each other. Although this system involved many more moving parts than the hydraulic system, these would all be above ground and easily accessible, so it offered easier and cheaper maintenance and a longer working life.

As the entire weight of the caissons and counterweights would now be borne by the superstructure of the lift, this would have to be greatly strengthened, and put on much stronger foundations. However, by building a separate stronger superstructure around the original lift frame, Saner promised to achieve the conversion with only three short periods of closure to traffic.

The new superstructure consisted of ten steel A-frames, five on each side of the lift, which supported a machinery deck 60 ft (18 m) above the river level. The electric motors, drive shafts and cast-iron headgear pulleys were mounted on the machinery deck. Wire ropes attached to each side of each caisson passed over the pulleys to 36 cast iron counterweights, 18 on each side. Each counterweight weighed 14 tons, so that 18 counterweights would exactly balance the 252 ton weight of a loaded caisson. The electric motor was required to overcome friction between the pulleys and their bearings. A motor was installed, but normal operation only required about half of this power.

In addition to new foundations and superstructure, the conversion also involved converting the wet dock at river level into a dry dock and strengthening the aqueduct between the lift and the canal. The original caissons were retained, but modified to take the wire ropes that now supported them on each side.

The conversion work was carried out between 1906 and 1908. As Saner had promised, the lift was only closed for three periods during these two years, for a total of 49 days. The converted lift was formally opened on July 29, 1908 (although one caisson had in fact been carrying traffic on electrical power since May 1908 while the second caisson was being converted) .

Operation after conversion

After conversion to electrical operation the boat lift was successfully operated for 75 years. Regular maintenance was still necessary. In particular, the wire ropes supporting the caissons suffered from fatigue as a result of repeated bending and straightening as they ran over the overhead pulleys, and had to be replaced quite frequently. However, the maintenance was simpler than before because the mechanism of the electrical lift was all above ground. It was also less expensive because the caissons were now designed to be run independently, so most maintenance operations could be carried out while one caisson remained operational, thus avoiding the need to close the lift entirely for any extended period.

Another regular maintenance job was repainting. The new superstructure of the converted lift was found to be susceptible to corrosion. To reduce this corrosion the entire lift was painted with a protective solution of tar and rubber, which had to be renewed every eight years or so.

During 1941 and 1942 the hydraulic rams of the original lift, which had been left in place in their shaft beneath the dry dock constructed during conversion, were finally removed in order to salvage the iron .

During the 1950s and 1960s the commercial traffic on British canals declined. By the 1970s the Anderton Boat Lift traffic was almost entirely recreational, and it was almost unused during winter months .

Closure

During repainting work in 1983 extensive corrosion was found in the lift's superstructure, and it was declared structurally unsound and closed .

Restoration

A modified version of the original hydraulic system was reinstated, however, after restoration work in 2002. The 1906-1908 external frame and pulleys have been retained in a non-operational role.

See also

References

External links

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