Royal Sovereign Lighthouse removal
By Robert Race, Senior Project Engineer
In the early hours of 6 November 2024, the final section of the central pillar of Royal Sovereign Lighthouse was successfully removed.
The final offshore lift had been scheduled to coincide with calm seas. In fact, the seas that night were so calm that a casual observer on the JB119 jack-up barge might have been forgiven for not properly appreciating the host of challenges that the delivery team had faced in the execution of this final phase.
A closer look, however, would begin to reveal the complexity of the operation. The swift currents, highlighted by the speed at which the resting seagulls floated past the jack-up, posed significant challenges for the diving team. Their tasks included core drilling holes for the lifting trunnions on each of the nine cut sections and positioning cutting wires, all within an hour’s workable conditions on either side of slack tide. That is, if the sea-state allowed them to…
As expected, it was the sea state that ultimately dictated the pace of progress. Whether it was diving, cutting, lifting operations or even routine tasks such as team members gaining access to the jack-up – progress was completely at the mercy of the sea-state and wind conditions.
Engineering solutions, like the substantial and bespoke cutting frame that was lifted and fixed around the pillar would help maximise the working windows above water but ultimately there were certain conditions where ‘downing tools’ was the only safe thing to do.
During the offshore elements of Phase 2, JB119 stoically remained at the location through several storms. One storm in particular, the ferocity of the winds and the sea state it generated were much greater than anything that had been forecast. It was fascinating to listen to the bargemaster, the person responsible for the jack-up, talk about the thrill it gave him as the barge was rocked by wave after wave. The faces of his colleagues during his telling of that tale showed they did not share it.
The pillar’s robustness presented a constant challenge to the ‘diamond-encrusted’ wire that was employed to cut through the various sections of pillar. The wire would generally make good progress, despite the very high strength concrete but would often become frustrated when the wire became snagged and occasionally broken by a small number of loose tendons as they rattled around inside their ungrouted sheaths.
As the cutting contractor made their progress down the pillar, each new section cut told a different story. The top cut section bore the scars from separation from the topsides during Phase 1. Sections 2 and 3 contained the access stairs up which a previous generation of lighthouse keepers would ascend and descend during their reliefs from station.
Sections 4, 5 and 6 proved particularly troublesome as these were double-thickness (and therefore double the mass). They contained the lower part of the upper section as well as the upper part of the lower section. The material used to create the collared joint between the two, contained a particularly high flint content. Another headache for Robore, our particularly determined cutting sub-contractor.
Section 7 which contained the recently purged and cleansed fuel tanks, would be the first predominantly submerged section to be cut and lifted. This brought with it a new set of challenges as these activities would become especially reliant on not just calm conditions but sustained calm conditions – a tall ask for October. The contractor’s lifting calculations were carefully scrutinised throughout to ensure the sections being lifted were within the capability of the jackup’s crane.
Sections 8 and 9 were lifted onto the jack-up barge together, allowing their separation to be performed from a protected position on board. It was these sections, along with the bespoke cutting frame that would form the final lifts from JB119 onto the waiting NP626 flat-top barge for transit back to the port of Shoreham.
Once ashore, demolition of the previous sections was already underway and, as of 27 November 2024, the entire demolition of the pillar sections had been completed.
A very high proportion of materials produced during the demolition of both pillar and topsides will be used, with a whole project recycling rate of 99.05% with Phase 2 in particularly recycling 99.96% of its materials.
Editorial note:
Published by kind permission of the author ©
and the Corporation of Trinity House, London ©.
An indication of the enormity of the contractor’s craft Gulliver. Slicing through the pillar with diamond encrusted wire.
Rapporteur: Paul Ridgway.