7.2 Blackout & Blackout Recovery

What “blackout” means on a DP vessel

In DP language, a blackout is total loss of main electrical power to the main switchboard(s) — and therefore to thrusters, large consumers, and most ship systems. Without bus power there is no thruster force. The vessel becomes a drifting object under wind, wave, and current (see drift-off in the next section).

Blackout is not:

• loss of all position references only,
• failure of one gyro or wind sensor,
• navigation-light failure alone,
• a single generator trip while another section still feeds thrusters (that is a partial power loss / section failure, serious but not full blackout).

Exam stems often mix these. If the stem says thrusters have no power and the main board is dead, answer blackout. If thrusters still run on the other ring, do not call it total blackout.

Why blackouts happen (exam-useful causes)

Blackouts arise from generation, distribution, or load problems — often combinations:

• generator overload / underfrequency cascade,
• short circuit with failed discrimination (especially closed common bus),
• simultaneous loss of online sets (fuel, cooling, control air, common auxiliaries),
• human error (wrong breaker, inhibited protection, manual trip),
• PMS / automation failure plus high demand,
• industrial load step without reserve.

Understanding causes helps prevention (spinning reserve, open bus for critical work, healthy PMS). Recovery procedure, however, is largely cause-independent at the first minutes: get power and controlled thrust back.

UPS: what survives the blackout

Uninterruptible Power Supplies (UPS) feed DP process stations, operator stations, selected sensors (gyros, MRUs, some PRS receivers), and network gear for a limited duration. UPS purpose:

1. Keep the control brain alive so modes, alarms, and displays remain usable.
2. Avoid cold reboot of DP computers during a short power dip.
3. Support orderly recovery when main power returns.

UPS does not power full thruster motors for station-keeping. Believing “we still have DP because screens are on” while the main board is black is a fatal misconception. Screens on UPS with dead thrusters = drifting vessel with a working HMI.

Blackout recovery priorities

Vessel-specific blackout recovery procedures (engine room and bridge checklists) rule, but exam and industry logic share a priority order:

1. Recognise and raise the alarm — blackout declared; stop critical external work (diving, heavy lift, close approach) per ASOG/emergency plan.
2. Restore electrical generation — emergency/standby generators start; engineers clear faults; breakers closed to re-energise bus sections per procedure.
3. Restore thruster power carefully — feed thrusters only when voltage/frequency are stable and drives ready; do not slam full thruster demand into a fragile plant.
4. Re-establish controlled thruster use — manual thruster/joystick or controlled DP modes as procedure allows; check enables and power limits.
5. Re-enable PRS carefully — bring references online only when power and control are stable; avoid flooding a recovering controller with wild measurements.
6. Regain position / clear the hazard — move to a safe location if required; then rebuild Auto DP and footprint confidence.
7. Record and debrief — log times, actions, and plant state after the vessel is safe.

[!IMPORTANT] First priority is almost always re-establish electrical power so thrusters can restart. Re-entering a worksite track, finishing the logbook, or recalibrating references is not first while the board is dead.

Prevent thruster surge on recovery

A common secondary incident is thruster surge (or drive-off-like behaviour) when power returns: thrusters spin up hard because setpoints, gains, or residual force demands from before the blackout are still large, or because Auto DP is re-enabled with poor references. Prevention measures the exam expects you to reason about:

• Confirm control mode before thrusters are enabled (often joystick/manual or thrusters zeroed per company SOP).
• Check position/heading setpoints match present reality if entering Auto DP.
• Bring PRS online gradually; verify quality before high weighting.
• Observe PMS load limits and spinning reserve; do not demand full weather capability on one weak genset.
• Coordinate with engineers so frequency and voltage are healthy before large thruster ramps.
• Watch for frozen or stale pre-blackout commands in some system designs — follow manufacturer recovery steps.

Operator procedures: bridge and engine room as one team

Blackout recovery is not a solo DPO software exercise. Typical operator responsibilities:

• Immediately reduce operational risk (stop divers, clear ROV, inform OIM/client per emergency matrix).
• Maintain situational awareness: drift direction, proximity to asset, depth of water, weather.
• Use emergency communications and thruster/joystick control as soon as power allows if needed to clear a structure.
• Follow the vessel blackout recovery checklist rather than inventing steps.
• Do not fight the engineer for breaker control; agree who owns generation restoration.
• After recovery, do not automatically resume critical DP work — reassess plant health, residual capability, and ASOG colour.

Worked recovery scenario

A closed-bus short blacks both sections of a PSV holding 30 m off a platform. Screens remain on UPS; thrusters stop; vessel begins drifting toward the jacket. The DPO sounds blackout, notifies the platform and master, and prepares joystick. Engineers start emergency generation and reclose breakers on one section first. When thrusters regain power, the DPO uses controlled joystick thrust to open distance from the platform before selecting Auto DP. PRS are re-enabled after power is stable; Auto DP is restored only with confirmed references and adequate online generation. The task remains aborted until the electrical fault is understood.

Exam traps for blackout items

Bottom line: blackout kills main power and thrusters; UPS only buys control continuity. Recover generation first, restore thrusters without surge, re-enable PRS carefully, and keep the worksite safe while the plant returns to a known healthy state.