The big idea: a ship is a power station that must never go dark

It is 14:42 on a feeder container ship. The pilot is on the bridge, the bow thruster is pushing at full power and the ship is 200 m from the berth. Three 900 kW diesel generators share the load in the engine room. Then generator 2 trips.

In the next ten seconds one of two things happens. Either the main switchboard sheds some cargo and hotel load and the ship carries on, or the two remaining generators overload, their breakers open and the ship goes dark beside the quay. The difference is not luck. It is the way the power and automation system was laid out and set up, and that is what this course is about.

One rule: supply must match demand, every second

A ship has no grid to lean on. Every kilowatt the consumers draw must come from generators running at that moment. So the whole system is built around one balance:

Keep a margin, because loads jump when a big motor starts, and because any running generator can trip.

One number

Manoeuvring with the thruster at full, our ship needs 1950 kW. With three 900 kW sets on line that is

Comfortable. Now one set trips. The same 1950 kW lands on two sets:

That is an overload. The preferential trips now switch off non-essential consumers in stages: air conditioning and galley first (110 kW), then the reefer containers (300 kW). The load falls to 1540 kW, or 85.6 % of the two remaining sets. Propulsion, steering and the thruster stay on. That is the job of the electrical design: lose comfort, never lose the ship.

Three layers

Every ship you join, from a bulk carrier to an LNG carrier, has the same three layers:

1. Power: generators, main and emergency switchboards, transformers, shore connection, batteries.
2. Distribution: breakers, feeders and starters that carry power to pumps, fans, thrusters, cranes and lights, sorted into essential and non-essential.
3. Automation: the alarm and monitoring system, the power management system (PMS), engine control, safety systems and fire detection, all joined by field cables and networks.

The loop

The PMS runs a simple loop, many times a second:

1. Measure the kW on each generator.
2. Compare with what is on line and with its thresholds.
3. Decide: start a set, stop a set, block a heavy consumer, or shed load.
4. Act through breakers and start commands, then repeat.

Keep this picture. Lessons 4 and 5 give you the numbers behind each step. The simulation in Lesson 7 runs this loop for a full voyage day, including the trip at 14:42.