Dropped Power Swivel

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Alert ID: 
Description of Task: 

While lowering the sea bed frame down the drill string to the seabed, the drill crew noticed a problem with the hydraulic winch (KPL 22).  The winch wire started to come off the drum and the Rooster Box and Dando dropped down the derrick to the drill floor with 298m of drill string connected and suspended below the vessel. The total weight of the Rooster Box, Dando and drill string was approx. 20MT (8MT equip + 12MT drill string). A Roughneck was on the drill floor immediately prior to the winch failure running a control cable.

Immediate Actions:

  • Original Work scope was terminated.
  • Efforts to recover drill string failed, 289m of drill string was towed to a safe location for release to the seabed.
  • Original winch was reinstated.

Investigations showed that during earlier maintenance an incorrect oil seal was fitted to the winch gearbox. This lead to a loss of oil from the gear box over time eventually causing a catasrauphic gear failure under load. 

The maintenance of the gear box had not been carried out to manufacturers specifications and there was no proof of adequate, ongoing maintnence checks.  When the contractor was engaged the company failed to implement it's own maintenance management system and no inspection of the vessel was done when accepting the vessel.  If proper systems had been in place for accepting and inspecting a new vessel, the lack of maintenance records or procedures would have been uncovered. Proper assurance and verification would also have identified the oil leak and potentially lead to a more robust inspection of the gear box.

The assumption had been made that because the operation was not a drilling operation, the normal checks undertaken when bring in a drilling contractor did not apply for this type of operation.

Lessons Identified: 

Vessel on hire surveys to consider all aspects of the work and not just Marine.

Vessel contractor to did not conduct formal risk assessments for new contract (and generic assessment did not include safe positions of personnel during tasks).

Contractor’s Management of Change was not applied prior to changing winch (which was not a like-for-like change).

Company Drilling Representatives will be present when performing Soil Boring activities.

Contactor’s Planned Maintenance shall take cognizance of manufacturers recommendations.

Communication failures between multi discipline teams resulted in gaps in contracting, acceptance and start ups for Soil Boring operations.

No worksite acceptance and inspection criteria in contracts. 

No specific International Guidance on Soil Boring of vessels, inspection criteria to be defined  by 3rd party drilling  rig inspection vendors and made specific for soil boring drilling packages.


Offshore soil boring operations are very similar to drilling operations, however this had not been recognized and in house drilling expertise is now utilized in current and future operations both in planning and execution.

A review  has been conducted in-Country to ensure SCM, Contract Users and other specialist departments (Drilling) are present during pre-tender evaluation, kick off meetings and execution.

Language will be inserted into all contracts where company has exposure to include acceptance criteria that requires all agreed critical action items are closed prior to start up as per a drilling contract.

Competent client and contractor representatives must be present for all pre-mobilization risk assessments, including those who will supervise the (Drilling) works including Company Safety Advisors.

Specific Equipment: 

Soil boring vessel hoisting equipment


Incident consequence: 
Seismic/survey operations
Specialist vessel eg diving, construction, survey
Cause of accident or incident: 
Collapse, overturn or failure of lifting equipment