Blackout During Maneuvering in a Narrow Channel
A twin-screw coastal vessel is transiting a narrow channel at night at half ahead when the main switchboard trips. Both generators stop, the steering gear loses power, and emergency lighting comes on. The engineer on watch reports that the No. 1 generator had been carrying about 85 percent load and the No. 2 generator was on standby, not paralleled. The blackout occurred shortly after the bow thruster was started. The vessel still has headway and is drifting toward the channel edge. The master is on the bridge.
1. Give the immediate priority actions and explain the likely cause of the trip.
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Immediate priorities are to restore control of the vessel and then power.
- Bridge and engine room communicate by whatever means remain (sound-powered telephone, VHF on a working set, or runners).
- The master should use remaining rudder authority and engine orders; the engineer should attempt to restart the emergency generator if it has not started automatically, and confirm emergency lighting and steering gear emergency supply are functioning.
- Restore main power by starting a generator from dead ship, taking care to reset tripped breakers and confirm the switchboard is clear of faults before closing.
Likely cause: starting the bow thruster imposed a large step load on No. 1 generator, which was already at 85 percent. The resulting overload or frequency/voltage dip probably tripped the generator breaker, and the loss of load may have shut down the prime mover. No. 2 was not paralleled, so there was no reserve to absorb the step.
The lesson is that heavy consumers should not be started without adequate spinning reserve and, where fitted, load-shedding or thruster interlocks should be verified.
2. Explain how you would re-establish power safely and what checks you would make before answering bridge telegraphs.
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Re-establish power in a controlled sequence:
- Confirm the cause of the trip and reset protective devices only after the fault is understood.
- Start a generator locally, bring it to rated voltage and frequency, and close to the main switchboard.
- Start a second generator and parallel it so there is reserve before restoring large loads.
- Restore essential services first: steering gear, navigation lights, alarms, and engine controls. Bring in large loads such as thrusters and pumps progressively.
Checks before answering telegraphs:
- Steering gear is powered and tested through its full range with the bridge.
- Main engine control and safety systems are live and no shutdown has latched.
- Auxiliary systems needed for propulsion (cooling, lube oil, fuel) are running.
- Communication with the bridge is confirmed.
Only then should the engineer acknowledge engine orders. The master should be told the vessel's propulsion and steering status in plain terms.
3. Recommend how the watchkeeping and generator management should change for the rest of the transit.
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For the remainder of the transit:
- Run both generators in parallel through the narrow channel so that thrusters and steering gear have spinning reserve.
- Set up load-dependent start or load shedding if available, and confirm the thruster interlock prevents starting when reserve is insufficient.
- Post a second engineer in the engine room during maneuvering, with a clear understanding of who is in charge of the switchboard.
- Agree a bridge-engine room communication protocol and a contingency plan for a second blackout, including anchor readiness.
- Record the event, the cause, and the corrective actions in the log, and raise a defect or near-miss report for the company.
After the transit, the incident should be reviewed on board so the sequence is understood and the generator management practice is corrected.