Question 1

A DP2 offshore crane vessel has two wind sensors fitted on the mast. During operations, one wind sensor fails and returns zero wind speed and direction. The DPO is aware the remaining sensor is reading 22 knots from the SW.

How does the DP system use wind sensor data, and what is the consequence of accepting a failed zero-reading sensor?

Accepted Answer

The DP system uses wind sensor data as a feedforward input to anticipate and pre-compensate for wind forces before they create a position error — a sensor reporting zero wind will cause the DP system to under-compensate for actual wind load, potentially leading to position excursion before the position error loop corrects DP systems use wind sensor data for feedforward (wind compensation) — the system pre-calculates the expected force from wind and pre-loads the thrusters accordingly, before position error develops. If a faulty sensor inputs zero wind and the DP system accepts or averages it, wind compensation will be underestimated, leading to a windward drift before the position feedback loop catches up. The DPO should disable or exclude the failed sensor from the DP wind input and monitor position more closely. In heavy wind conditions, a failed wind sensor increases position variance significantly.

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.