HMNB Portsmouth – on site at the historic home of the Royal Navy

 30 November 2020
HMNB Portsmouth – on site at the historic home of the Royal Navy

This summer we undertook one of our more unusual projects in 2020. At first sight, the installation of a 126.5m line of eleven, 3m wide, heavy-duty System 21 pontoons with mesh decking and GRP handrails alongside a quay wall would seem straightforward. The new facility for BAe Systems is for the use of general harbour work boats and replaces one we installed on the same footprint 25 years ago. However, the fact that it took place within the Portsmouth Historic Dockyard made the project a special, and challenging, one.

Firstly, the heritage status of the site demanded special care and part of the remit was that we had to return the harbour wall to its original pristine state. This was done by carefully removing the existing wall mounts and associated fixtures that had held the previous pontoons in place and then repairing the wall to standards set by Portsmouth City Council Heritage. As part of this process, we had to position three instruments along the wall to monitor the vibrations to ensure that no damage was done. This achieved, we then provided a more heritage-friendly solution for holding the new dock in place with the Walcon Wizard piling barge driving piles directly into the basin floor instead.

The second unusual aspect of the project was that, given the dockyard’s history, we had to undertake an unexploded ordinance (UXO) survey of the seabed in the basin. We brought in some expert assistance and deployed the Walcon Wizard once again, this time carrying high-tech 3-D imaging equipment capable of ‘seeing’ five metres into the seabed. With its ample unencumbered deck space and excellent manoeuvrability, it makes an excellent diving platform, and its crane was ideal for lowering the imaging equipment into the water. The process took three days to complete. No bombs were found.

Thereafter the installation of the pontoons was straightforward with completion in late November. The Walcon Warrior and Wolf barges were used to remove the old pontoons and bring in the new by water.

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