A blackout is the complete loss of the ship’s main electrical power supply. When this occurs, the main engine usually shuts down immediately because it depends on electrical power for essential control and support systems. A blackout can quickly develop into a serious emergency, particularly if the vessel is navigating through narrow channels, congested waterways, near the coastline, or operating in rough weather conditions where propulsion and steering are essential for safe navigation.

During attempts to restore power, engineers should avoid repeatedly trying to restart the generators without first identifying and correcting the fault. Continuous unsuccessful starting attempts can completely deplete the compressed air stored in the main air bottles. If the air bottles become empty, the ship enters a dead ship condition as defined by SOLAS, where neither the generators nor the main engine can be restarted until compressed air is restored.

Immediately after a blackout, the emergency generator is designed to start automatically and supply power to essential emergency services. This emergency electrical supply supports critical equipment such as emergency lighting, communication systems, navigation equipment, and safety devices. However, the main propulsion machinery cannot be restarted until the ship’s main generators (alternators) have been restored and synchronized with the main electrical system.

The following actions should generally be taken during a blackout, with modifications depending on the type and operational condition of the vessel:

• Sound the general emergency alarm.
• Determine the cause of the electrical power failure.
• Assess the impact of the blackout on the ship’s machinery and essential systems.
• Take appropriate measures to restore electrical power and propulsion.
• Display Not Under Command (NUC) lights or day shapes to warn nearby vessels.
• Prepare to anchor if water depth and location permit.
• Continuously monitor weather conditions and forecasts to anticipate additional hazards.

In addition to these actions, the engineering department should follow a blackout checklist to systematically identify the fault, carry out corrective actions, and safely restore the ship’s electrical and propulsion systems.