Cause & Consequence
- Failure of vessels or pipework
Onshore office, support base, heliport
Incident Info Source
Neil Smith - Maersk
Specific Incident Equipment
The vessel has a Tentech turret just forward of midships equipped with a 10 point
mooring system with 84mm diameter, K4 grade chains with a design Break Load
(BL) of about 730 tonnes. The turret is maintained in a fixed orientation, the vessel
rotates around it.
The incident highlights the need for duty holders to be aware of the potential for
loss of heading & position on vessels fitted with Position Mooring (PM) systems.
1. PM System
The Class driven maintenance and functionality checks for a moored PM vessel are
less stringent and comprehensive than those implemented by full dynamically
positioned vessels such as DSVs. It may be prudent to consider employing a similar
philosophy for moored vessels.
During this incident a number of inputs to the PM model were inaccurate,
contributing to error forces building up within the model and resultant incorrect
forces being applied by the PM system.
Duty holders may wish to review their processes and procedures to ensure that:
the data recording system is sufficient; the model is reset or refreshed at a suitable
frequency; the maintenance and functionality checks are suitable and sufficient;
operators are drilled in the actions necessary in all foreseeable emergency
scenarios; and inputs to the PM system are accurate, reliable and have sufficient
2. Mooring System.
The basis of design of a PM vessel mooring system assumes that the vessel will not
lose heading control, so will remain within approximately 10 degrees of head into
Analyses of the mooring system showed that the forces placed on the anchor lines
would have approached or exceeded the break load of the chain at angles seen
during the incident.
Duty holders may wish to review their mooring system’s failure mode analysis in
order to ensure that the forces applied to the vessel, at reasonably foreseeable
angles and environmental conditions are understood and appropriate procedures
and processes are in place to manage the risks from loss of heading and those
3. Anchor Chains
During this incident anchor chain number 7 failed at the flash butt weld of one of its
links. This failure mode is unlikely to be picked up by visual inspection.
Duty holders may wish to review their inspection and discard criteria for anchor
chain, to ensure they remain appropriate in the light of this failure type.
4. Power Management
During the incident, the power management set up was not optimal for the
prevailing weather conditions.
Duty holders may wish to review their power management procedure and processes
to ensure that they are appropriate for all reasonably foreseeable operating and