Question 1

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 2

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.

Question 3

A small offshore support vessel with DP Class 1 notation is asked to assist in a long-term mooring operation near an unmanned platform in moderate weather. The operator argues DP1 is sufficient because "it has a DP system."

What is the key limitation of DP Class 1 that the operator should understand?

Accepted Answer

DP Class 1 provides no redundancy — a single equipment failure may result in loss of position, making it unsuitable for operations where loss of position carries significant risk DP Class 1 has no redundancy requirement. A single failure — one generator, one thruster control card, one gyro — can cause loss of position with no backup available. This makes DP1 unsuitable for operations near structures, with divers in the water, or where sudden loss of position could cause injury, structural damage, or environmental harm. Activity-specific risk assessments (ARA) and ASOG should reflect this limitation explicitly.