Ship Engine Room and Onboard Power

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Ship Engine Room and Onboard Power

In the engine room, systems for propulsion and power supply work together. The main propulsion system provides the power for movement, while the ship’s electrical network supplies electrical equipment such as pumps, ventilation and control systems. Depending on the ship, electricity is generated by auxiliary engines or partly by the main engine. Propulsion and onboard power are therefore connected, but serve different purposes.

Main propulsion and auxiliary units

In a diesel-mechanical propulsion system, the main engine drives the propeller via a shaft system. Separate auxiliary engines can drive generators and supply electricity to the ship’s electrical network. In an electric pod propulsion system, the motor is housed directly in a pod attached to the propeller.

Where the electrical power comes from

A shaft generator uses the rotation of the main engine to generate electrical power and feed it into the ship’s distribution system. The generator can be connected directly to the main shaft or via a gearbox. In power-take-off (PTO) mode, power is drawn from the main engine and converted for the ship’s electrical network. This can partly or fully replace the use of separate generators if the main engine is operated under a suitable, steady load and supplies the required electrical power. A frequency converter makes it possible to provide a stable electrical frequency even when the shaft speed varies.

The ship’s distribution system delivers electricity to consumers. These include pumps, lighting, ventilation, heating and cooling, as well as control and navigation systems. Demand varies according to operating conditions: while underway, propulsion and onboard consumers operate simultaneously; in port, the power supply may be organized differently.

Electrical consumers and shore power

At berth, shore power can supply the ship with electricity from the local grid. Connected ships can use it to power auxiliary systems such as lighting, air conditioning and refrigeration, and switch off the onboard engines used for those systems. The shore connection and the ship must be equipped for this connection. Shore power supplements the onboard supply during a port stay and should be distinguished from power generation in the engine room.

The Queen Mary 2 offers a concrete example of how advanced propulsion and power systems come together on a large passenger ship.