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The reach of giant floating shearlegs gives access to difficult sites
Large components can be prefabricated on land rather than assembled in situ over water
Europe's largest shearlegs will be deployed on the Tyne later this year
November's installation of the Gateshead Millennium Bridge promises to be one of the most spectacular events ever seen on the Tyne. At 7am on a day when winds are below Force 5 and the swell on the river is no more than 500mm high, the Asian Hercules II, Europe's biggest floating sheerlegs, will leave her downriver berth and begin to manoeuvre into position alongside Amec's Hadrian offshore yard, near Wallsend.
AHII's massive A-frame, with its 3,200t capacity, should pluck the 1,100t, Gifford-designed, Watson Steel-fabricated 'eyelid' structure off the quayside shortly after midday. Then the 8km voyage to the bridge site will begin.
Negotiating the twists and turns of the Tyne will not be easy.
The AHII is more than 90m long with a beam of nearly 45m, and it will have 125m of bridge structure projecting from its bluff bows. Nevertheless, operator Smit Transport & Heavy Lift is confident the planned two-hour journey will be completed on schedule and that by around 6pm the Millennium Bridge will be in position across the Tyne.
Smit sales manager Remko de Boer says the operation typifies the benefits offered by floating sheerlegs of this type. 'It allows the contractor to do all the critical work onshore under controlled conditions, with no safety worries, no temporary works, none of the problems of working over water.
'And because the vessel is self-propelled and has a shallow draught compared to other types of marine lifting equipment, it can usually pick up the section from the fabrication yard and take it straight to the bridge site.
Double handling is eliminated.'
Smit's Rotterdam-based fleet of five floating sheerlegs has been involved in a number of similar bridge projects in Europe recently, including the installation of the notorious Passerelle Solferino across the Seine in Paris (it was closed after excessive sway on its opening day).
One of Smit's smaller units brought in and installed the steel bowstring structure crossed by all river-borne visitors to the Millennium Dome.
De Boer says a project in the Spanish port of Tarragona is another good example of the way floating sheerlegs can speed construction.
'A new steel bascule bridge was planned, consisting of two 450t approach spans and two bascule spans of around 700t each. We deployed Taklift 7, a sheerleg of 1,200t capacity. It picked up all the spans from the quayside fabrication yard, transported them through the port and installed them. Both approach spans and one bascule span went in on the first day, with the last bascule going in the next morning.'
Awkward asymmetrical loads like bascule spans and eyelid bridges are much easier to handle with sheerlegs, de Boer adds.
Each frame supports several independent lifting blocks, which means no special rigging arrangements are needed to accommodate unusual centre of gravity locations.
Giant floating sheerlegs were originally developed for salvage operations, and the Smit fleet still carries out many such assignments. Later on they found many applications in the offshore oil sector, routinely used to lift modules onto platforms - and to dismantle them.
But a downturn in the North Sea has forced Smit to look for more work in the civils sector. This has coincided with a demand for greater lifting capacity, in landbased cranes as well as floating sheerlegs.
'We were planning to build a new, bigger vessel when we discovered the AHII in the Far East, ' de Boer says. 'Chartering it for three years will enable us to test the market for such a vessel.
'It got off to a good start. On its way here from Singapore to Rotterdam it stopped off in Barcelona to install two bascule bridge spans weighing 1,200t each.'
AHII's main A-frame is 90m high, providing a lifting height of 76m. With a flyjib rigged lifting height goes up to 112m but capacity drops to 1,600t.
Fully loaded, AHII draws more 7m. At the other end of the Smit range, the Amsterdam, with its 300t maximum capacity, draws just 3.5m fully loaded.
And with a beam of under 18m, Amsterdam can get into places denied the much bulkier AHII.
However, the four azimuth thrusters - basically giant outboard motors capable of being rotated through 360degrees - projecting from AHII's flat bottom endow the giant vessel with maximum manoeuvrability. The trip up the Tyne, wind and weather permitting, is scheduled for 6 November. It should be quite an event - and NCE will be there.
Smit Transport & Heavy Lift BV Tel 00 31 10 454 9911 www.asianlift.com.sg