Question 1

Before commencing a sensitive DP operation on a DP2 vessel, the senior DPO is conducting a consequence analysis test. A junior DPO asks what the "Worst Case Failure" (WCF) means in practice.

Which statement best describes the WCF concept for a DP2 vessel?

Accepted Answer

WCF is the single active component or system failure that would result in the greatest loss of DP capability — the DP system must be able to maintain position after this failure occurs The WCF (sometimes called Worst Case Failure Design Intent — WCFDI) is the single failure that removes the most thrust or capability from the DP system. For a DP2 vessel, the system must demonstrate — through consequence analysis — that it can still maintain position after the WCF occurs. The consequence analysis test simulates this failure at the worksite to confirm the remaining thrusters and power have adequate margin. If the test fails, the ASOG should dictate that operations cannot proceed.

Question 2

A DP Class 2 vessel is operating on a subsea construction project. The chief engineer asks whether the vessel can continue operating in the event of a single active component failure.

What does DP Class 2 guarantee in this situation?

Accepted Answer

The vessel can maintain position after a single failure of any active component or system, provided redundant systems are in place and operational IMO MSC/Circ.645 and IMCA M103 define DP Class 2 as: no loss of position following any single failure of an active component or system. Redundancy in active components is required — thrusters, generators, UPS, switchboards. Fire/flood protection requires DP Class 3. Static components (cables, pipes) are not covered by the single failure criterion.

Question 3

A semi-submersible drilling rig is classed DP Class 3 and operates in deep water on a well with well control implications. A trainee DPO asks what the key distinction is between DP2 and DP3.

Which statement correctly describes the DP Class 3 requirement?

Accepted Answer

DP3 requires redundant systems to be located in separate watertight compartments with physical separation, such that a single fire or flood cannot affect both systems simultaneously DP Class 3 extends the single failure criterion to include fire and flooding in any one compartment. This demands physical separation — redundant power systems, DP control systems, and thrusters must be arranged in separate fire and watertight subdivisions. A cable fire that destroys one entire DP system must leave the other fully capable of maintaining position. This is the "worst credible failure" standard.