Question 1

A DP2 platform supply vessel is holding position very close astern of a pipe-lay barge that is also operating on DP. The PSV's DP system is commanding high stern thrust to maintain position against a strong current. The DPO notices the position is becoming increasingly difficult to hold despite high thrust demand.

What phenomenon is the most likely cause?

Accepted Answer

Thruster interaction — the pipelay barge's thrusters are producing a wash that is acting directly on the PSV's thrusters, degrading their effective output Thruster interaction — where one vessel's thruster wash directly impinges on another vessel's thrusters — is a documented cause of DP incidents in close-proximity multi-vessel operations. IMCA has recorded cases where a PSV was forced off station by the thrust wash of a pipelay vessel. The DPO must understand the relative positioning of all nearby DP vessels, their thruster configurations, and the current/wind direction to anticipate interaction effects. The ASOG should address minimum clearance distances.

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.