Question 1

A DP3 drilling vessel is on station in 1,800m water with a riser connected. Without warning, Gyro 1 shows a sudden 15° change in heading while the vessel's actual heading, confirmed by all other instruments, has not changed.

What is the immediate risk to the vessel if this gyro jump is accepted by the DP system?

Accepted Answer

The DP system, believing the vessel has yawed 15°, will command thrusters to correct the perceived heading error — this can result in a sudden, large unintended movement in the direction opposite to the perceived yaw, which may stress the riser and cause a position excursion The DP control system uses heading from the gyrocompass to resolve forces into correct thruster commands. A sudden 15° heading "jump" on an accepted gyro is interpreted as a real yaw — the DP system responds by commanding thrusters to correct it, introducing a large transverse force on the vessel. This can result in a sudden, unintended position excursion — potentially putting riser stress beyond limits, endangering divers, or driving the vessel toward a structure. IMCA incident data records multiple events where gyro jumps caused drive-offs. DPOs must know how to rapidly reject a faulty gyro input.

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.