Devonport Prepared to Receive Astute

(April 23, 2010) -- As Astute, the first of the new generation nuclear powered attack submarines (SSN) for the Royal Navy, undergoes its first set of sea trials, a milestone has been reached in developments by the UK's largest naval support provider, Babcock, in preparation for the through-life support of the new submarine.

Babcock, the company responsible for supporting the Royal Navy's entire submarine flotilla at Clyde and Devonport, has this month (April) completed installation of a new docking cradle, officially opened this week, which will enable the Astute Class Submarines to be received within Babcock's nuclear docking facilities at Devonport Royal Dockyard. The new cradle is required as Astute is considerably larger in mass and geometry (about 15% bigger in length and diameter) than the Swiftsure and Trafalgar class SSNs. This cradle, in 15 Dock, is in addition to the docking capability in the shiplift at Clyde.

This latest milestone at Devonport follows substantial work undertaken under the Astute Readiness Programme by an integrated MoD/Babcock team at Clyde, where the new submarines will be base-ported. Work here has included checking and modifying the infrastructure to support the new submarine class, amending the Site Safety Cases to encompass the new boat, provision and acceptance of support equipment specific to Astute, and training base staff to enable them to support and maintain the new vessel.

At Devonport, the existing cradle - on which the submarine is supported while in dry dock - had to be extended to accept the new larger submarine with a further nine cradle blocks which have been designed, manufactured and installed by Babcock, including four wing cradle blocks at the forward and aft end and an additional keel cradle at the aft end. Each cradle block assembly weighs some 22.5 tonnes. A full set of wooden cappers (which sit on top of the cradle blocks and are hand cut into shape to replicate the profile of the submarine hull) has also been manufactured and fitted.

In addition to the cradles and cappers, base plates have also been designed and manufactured. These are set into the dock floor and secured by anchors - a process that involved hydro-demolition to expose the heavily reinforced dock floor. The cradles are bolted down to the baseplates, and can be removed as required, providing the flexibility to accommodate various classes of submarine.

Each cradle block must be able to resist shear, tension and turning moments, while resisting a defined seismic event. Numerous physical parameters or external forces (of which seismic events are one) can influence the behaviour of the submarine on the cradle, and therefore influence the loads to which the cradle reacts. The cradle design has undergone a rigorous process including Finite Element Analysis modelling and Independent Technical Assessment to confirm that it can resist these factors and will keep the submarine upright in defined conditions.

The new Astute docking cradle is a Category 1 structure (the term used for any structure, system or component which forms a principal means of ensuring nuclear safety), and as such has undergone the highest level of quality control and inspection.

Source : Babcock International