What is Worst Case Failure Design Intent?
Worst Case Failure Design Intent, often shortened to WCFDI, describes the most severe single failure that a dynamic positioning vessel is designed to withstand without unacceptable loss of position capability.
For DP2 and DP3 vessels, understanding the WCFDI is essential because it links the vessel's design, FMEA, protection philosophy, power system configuration, thruster capability and operating limits.
Failure Identification
The first step is to identify credible single failures and determine which failure has the greatest consequence for position keeping capability.
Power & Thruster Consequences
The WCF normally affects available power, thrust or control capability. This may involve loss of a switchboard section, generator group, thruster group or control system element.
Open and Closed Bus Operation
The WCFDI may change depending on vessel configuration. Closed bus, open bus and split-bus operation should be assessed against the actual protection and redundancy concept.
Verification by Testing
The WCFDI should be supported by practical testing where safe and appropriate. Testing should confirm that the vessel response matches the FMEA assumptions.
Operational Limits
The WCFDI is closely linked to post-failure capability, environmental limits, activity specific operating guidelines and the vessel's DP operating procedures.
Common WCFDI Issues
- WCF not clearly stated
- Different documents giving different assumptions
- Modifications changing the original redundancy concept
- Testing not aligned with the stated WCFDI
Ricketts Marine Consultancy provides independent support for WCFDI review, DP FMEA review, redundancy analysis and annual DP trials preparation.
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