Complex Waterline Recovery Lift at Aberdeen South Harbour
As part of a marine decommissioning campaign at Aberdeen South Harbour, DeepOcean required the controlled recovery of a large subsea structure and its transfer onto the quayside.
The recovery presented a complex lifting challenge, with the load behaviour changing significantly as the structure transitioned from water to full suspension. Managing this safely required careful engineering, assurance and coordination across the marine, crane and quayside operations.
ASCO provided the lifting engineering and independent assurance needed to develop and execute a controlled recovery methodology, enabling the structure to be safely recovered within the available marine window and without disruption to the wider decommissioning programme.
Scope
Lifting Assurance, Training & Technical Support, Decommissioning
Location
Aberdeen South Harbour, Dunnottar Quay, Scotland
Duration
Project-specific operation
At a glance
- A complex subsea recovery at Aberdeen South Harbour required a controlled solution to manage changing load conditions through the waterline.
- ASCO provided independent lifting engineering and assurance to support safe, coordinated execution.
- Coordinated crane, marine, contractor and quayside activities through a single lift plan and defined communication structure.
- The recovery was completed within the available marine window, with no HSSEQ incidents, dropped objects or impact on the wider decommissioning programme.
Approach
ASCO provided independent lifting assurance throughout the planning and execution of the recovery, applying an engineering-led approach to identify and control the critical factors associated with lifting the structure through the waterline.
Pre-lift engineering and validation included:
- Verification and application of load data, centre of gravity, dynamic and weight growth allowances, and crane capacity at the required working radius.
- Assessment of ground bearing pressures, sling angles and load-spreading arrangements, together with development of rigging configuration
- Definition of wind and environmental limits, exclusion zones, and communication arrangements.
- Confirmation that the lifting arrangements met applicable LOLER and BS 7121 requirements.
This engineering process established the operating envelope for the lift and provided clear parameters for controlled execution.
Controlled Execution
Execution followed a defined sequence, beginning with a controlled trial lift and breakout before progressing to full recovery. Load behaviour was monitored through the transition from buoyancy to full suspension, with defined hold points used to confirm conditions before each stage. Slewing, taglines and load control were managed throughout to maintain control and minimise uncontrolled movement.
All contractors worked to a coordinated lift plan with clear roles, responsibilities and communication arrangements, aligning the crane, marine and quayside teams and reducing interface risk during critical recovery stages. A structured debrief and review followed the operation to capture learning and support continual improvement.
Impact
The subsea structure was successfully recovered and transferred to the quayside within the allocated marine window, with no delay to the wider decommissioning programme.
Through identifying and engineering the critical load transition before the lift commenced, ASCO established clear operating parameters for the breakout and waterline transition, reducing uncertainty and the risk of aborted lifts, re-rigging or additional planning.
The recovery was completed with:
- Zero HSSEQ incidents
- No dropped objects
- No environmental or marine safety events
- Full compliance with LOLER and BS 7121
By engineering the critical load transition and controlling the execution, ASCO helped deliver a safe, predictable and successful marine recovery.