Question 1

A semi-submersible crane vessel is using taut wire as a primary position reference system in 280m water depth. Operations have been running for 12 hours. The weather has picked up and the vessel has been making significant excursions, with the taut wire weight sometimes coming close to the seabed angle limit.

What is the critical limitation of taut wire that the DPO must manage in this scenario?

Accepted Answer

Taut wire is limited by the maximum angle the wire can deflect from vertical before the clump weight lifts off the seabed or the wire reaches its measurement limit — beyond this, the reference becomes inaccurate or fails entirely, and in deep water the wire catenary also introduces measurement error Taut wire relies on measuring the angle and length of wire from a deck-mounted gimballed sensor to a clump weight resting on the seabed. If the vessel excursion is large enough, the wire angle exceeds the sensor's measurement range, or the clump weight lifts off the seabed — at which point the reference fails. In deep water, the wire catenary (natural sag under its own weight) also introduces geometric error. The DPO must monitor excursion limits relative to taut wire capability and know the system's rated maximum angle and depth.

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.