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Rosyth Dockyard

1903 Rosyth selected as new deep water naval base

1909 Construction starts

1912 Work accelerated in response to German threat

1916 Construction completed and first vessel, HMS Zealandia, built

1917 Grand Fleet moved down from Scappa Flow

First World War Number 2 Dock notched to take HMS Hood's bow

1963 First nuclear submarine, HMS Dreadnought

1971 First Polaris submarine

April 1987 Babcock Rosyth Defence takes over

2002 Last nuclear refit programmed

SLAB SLIDE: Constructing the concrete modules for the new submarine cradle had to be carried out in parallel with the dockyard's ongoing submarine refit programme. Main contractor Nuttall decided to precast the slabs then move them into position.

'Originally the cradle was to be made of concrete baskets that could be floated in,' explains Nuttall area manager James Scobie. 'The problem was that the concrete sides and spine would make it difficult for people to work under the vessel.'

This led to the choice of a flat slab design without side walls. Initially the plan was to attach steel walls to the four sides of the slab. These would have given it enough buoyancy for it to be floated from the casting yard to the dock.

However, the contractor was unhappy with this idea: 'We had concerns about control of the floating process,' says Scobie, 'so we devised the dry slide alternative.'

This involved casting the four 29m long, 9m wide and 500mm deep, 350t flat slabs on raised beds beside their final location. Specialist subcontractor Heavylifts then dragged the slabs across to their final position using hydraulic jacks fixed to the dock walls.

Six steel sleds carried each module on three runways made from steel plates cast into temporary low walls running between the casting beds and the cradle's final location. It took a full day to slide each of the modules on to the concrete plinths.

Tolerances on the final cradle were about 1mm, less than the construction tolerances for each module.

'We used compressible pads under the isolation bearings with 11mm compression to take out the variations in the module surface,' explains Scobie. 'That ensured contact between the modules and all the isolators so that there is a solid load path to the boat.'

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