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Reversal of fortune

HERITAGE ENGINEERING: Anderton Boat Lift - After decades decaying in a field, one of Britain's most important working Victorian monuments is about to groan back to life. David Hayward reports from the River Weaver.

Engineers restoring the country's oldest boatlift at Anderton, Cheshire could be forgiven for not rushing to answer incoming phone calls. The delay could well help attract the few pounds still needed to fund this ancient monument's complex repair programme.

'Thank you for holding - and if you feel you could contribute to our restoration fund ask to be transferred to the Trust appeal office, ' says the recorded message as callers wait to be connected to a British Waterways site engineer.

But, the few thousand pound shortfall apart, a 20 year financial and technical battle to restore a waterway monument of world importance will finally be won this Easter. Next month the 127 year old structure will creak back into action; its two water filled caissons raising and lowering boats full of pioneering bank holiday tourists the 15m between the Trent & Mersey Canal and the River Weaver.

'Restoration of one of our most complicated working monuments has been a compromise between retaining the maximum original fabric and giving it a life for the new century.' says English Heritage regional inspector of ancient monuments Andrew Davison. 'It has proved an excellent example of British Waterways and English Heritage engineers working well together towards a common aim.'

His comments are more than bland praise. For two decades, ever since the Anderton Boatlift was all but abandoned after ignominiously grinding to a rustladen halt in 1982, its saga has been peppered with apathy, a stop-go funding crisis, total rethink on the restoration process and an increasing realisation that the structure was in a far worse condition than anyone imagined.

This chequered phase mirrored the boatlift's troubled working life. The now restored machinery, currently undergoing recommissioning trials, failed twice during operation and is consequently not one but two essentially separate structures.

Designed by eminent canal engineer Edward Leader Williams, the boatlift began work in 1875 as a slender wrought and cast iron frame enclosing two 23m long caissons each able to transport two narrow canal barges between the upper Trent & Mersey Canal and the 15m lower River Weaver.

Main cargoes were salt and china clay seeking a direct route along the canal from their Cheshire source and, via the lower river, to Liverpool and eventually markets in Ireland.

Each loaded 252t caisson was supported and raised by a single central hydraulically powered cast iron ram rising from an underground shaft. The shafts were linked allowing the two caissons to operate as a balanced pair, one lifting as the other lowered.

This system worked well for 30 years until hydraulic seals failed and a new electric lift mechanism was needed (see box). The rams were removed and caissons hung from ropes powered by overhead electric winches, counterweighted with cast iron ingots slung from the boatlift roof.

The change demanded a completely new structure to support an overhead working platform of cogs and pulleys. This 1908 steel frame surrounded and enclosed the original lift.

Electricity kept the caissons working until a routine inspection in 1982 revealed serious corrosion in the newer steel columns, then carrying all 1,000t live loading. Closure was inevitable and immediate.

The follow-on stagnation years began with owner BW taking the position that it was not in the business of restoring nonessential waterway machinery and could only contribute funds needed for routine maintenance.

They have ended with the £7M repair bill all but raised - most of it painfully through enthusiastic volunteer groups - and a client still able to contribute only the £1.9M equivalent maintenance costs. But BW now offers an equally enthusiastic team of site engineers acting, unusually for BW, as its own in-house main contractor.

'It was impossible to identify the work needed until we could dismantle the boatlift and structurally analyse all 100 main elements separately, ' says BW project manager Martin Clarke.

'Letting it out as a series of contracts would have doubled the time and cost, but this way allows more direct negotiations with EH.'

Equally unusual is the two year repair itself. Plans to restore the newer 1908 electrically powered version - the more normal EH principle with a listed structure - were scrapped when the true extent of frame replacement and alteration was appreciated.

Serious rusting of the 700mm diameter steel columns, revealed after blast cleaning, meant that around 60% of this outer frame would have had to be replaced. And modern electric lifting machinery would demand the addition of very visible backup safety brakes.

'Retention of the structure's historic fabric is more important than insisting on a particular mode of operation, ' explains Davison. 'So we allowed the 1875 hydraulically powered version to be reinstated and have kept the 1908 frame as a nonworking static monument.'

This meant providing new 38t steel rams centrally beneath each caisson, but otherwise renewing less than 3% of the surrounding structure. The weaker steel frame has its 72 overhead cogs back in place, but only for show. And removing the 1,000t live load of operating the caissons allows significantly less repair to corroded columns.

This flexible EH stance extended to the repairs themselves. The agency's firm stance on historical accuracy still held true and EH had to approve all 1,000 repair operations.

Bolts mimicking original riveted joints are round headed, even in the most invisible places.

And several small new window panes in a rebuilt timber control cabin must now be blocked up after a late look at early photographs revealed the original building not to be as symmetrical as thought.

But rationalising the approach aqueduct's poorly detailed drain tubes received a sensible nod of approval, as did not reinstating timber walling which had protected the structure from leaking caissons.

The boatlift's new role - one intended to make it self financing - will be primarily to entertain a planned 55,000 annual visitors each paying to enjoy 'with original creaks and groans' the canal network's only white knuckle ride.

Iron constitution

Anderton boatlift's two separate structures - an 1875 wrought and cast iron frame housing hydraulically powered caissons overlain by 1908 steel A- section columns supporting overhead electric pulleys - offers engineers a classic lesson in metallurgy. The 127 year old ironwork remains sound, while the younger rusted and pitted steel columns had lost up to 90% of their section.

But the steel frame escapes major repair as its role of caisson lifting is removed, along with over 60% of live loading.

Leakage from the 1875 leather seals in the ram shafts, which caused the original lift mechanism to be abandoned, was triggered when the cast iron rams became scored by grit. Resulting grooves were infilled with copper and tin which then, using the hydraulic fluid - acid rich river water - as an electrolyte, chemically attacked the iron ram itself, further increasing damage.

EH comments: EH has been closely involved throughout the project, from initial discussions over the principles of restoration, to monitoring the project on behalf of the Department for Culture, Media and Sport to ensure compliance with scheduled monument consent. EH also monitors expenditure for the Heritage Lottery Fund, which has provided the largest slice of funding, and has itself given a grant of £500,000.

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