Question 1

Before departing for a sensitive offshore installation project, the master reviews the vessel's DP capability plot with the lead DPO. The forecast shows wind at 28 knots from the south. The capability plot shows a significant asymmetry — the vessel can hold position in 35 knots from the north but only 22 knots from the south.

What does this asymmetry in the capability plot indicate, and what should the DPO do with this information?

Accepted Answer

The asymmetry indicates the vessel's thruster arrangement provides unequal thrust in different directions — the DPO must factor the forecast 28-knot southerly into the ASOG weather limits and may need to consider vessel heading to optimise capability The DP capability plot shows the maximum environmental force (wind speed, current, wave) the vessel can resist from each direction while maintaining position. Asymmetry reflects the thruster arrangement — a vessel with more azimuth thrusters aft will typically perform better heading into weather. With a forecast of 28 knots from a direction where the vessel's capability limit is 22 knots, the DPO must plan the worksite heading carefully, review the ASOG weather limits for that direction, and consider whether the operation should be deferred or the vessel positioned differently.

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.