Why PLC Logic, Network Timing, and Sensor Trust Decide Outcomes
Introduction — automation does not replace judgement, it compresses time
Modern ships are controlled by layers of automation: PLCs executing logic, SCADA systems presenting data, and field networks carrying signals from thousands of sensors. When these systems behave, ships feel calm and controlled. When they don’t, crews are confronted with alarm floods, contradictory indications, and disappearing control.
Automation rarely causes accidents directly. It shapes how quickly and clearly humans can respond when something else goes wrong.
What ship automation actually consists of
A typical marine automation stack includes PLCs handling real-time logic, remote I/O collecting signals, fieldbuses (Modbus, CAN, Profibus/Profinet) transporting data, and SCADA or IAS interfaces visualising status and alarms. Control power, network integrity, and sensor accuracy are all equally critical. If any one layer degrades, the entire control picture becomes unreliable.
Unlike mechanical systems, automation fails informationally first. The ship may still be running, but operators no longer know how well or for how long.
Timing, not speed, is the hidden vulnerability
PLCs are deterministic. Networks are not. As systems expand, polling delays, packet loss, and prioritisation errors creep in. A pressure transmitter that updates one second late can cause a control loop to overshoot. A delayed trip signal can allow thermal damage to escalate before protection acts.
These are not software bugs. They are architecture decisions.
🔧 Regulatory anchors (explicit)
IEC 60092-504 / 501 govern control and instrumentation power and segregation.
IACS UR E10 requires environmental and EMC robustness for automation equipment.
SOLAS II-1 Reg. 31 & 45 link reliable control to machinery safety and fire prevention.
Automation that loses integrity under normal ship conditions is a compliance issue, not an IT problem.
🔻 Real-World Case: Alarm Flood and Loss of Situational Awareness — MV Viking Sky (2019)
During the casualty aboard MV Viking Sky, crews reported simultaneous alarms across multiple systems as engines shut down and power collapsed. While automation reported faults accurately, the volume and simultaneity of alarms overwhelmed human processing at the worst possible moment.
The automation worked.
The human-automation interface failed to preserve clarity.
Investigators highlighted alarm management and prioritisation as contributors to delayed diagnosis.
Sensor trust — when “data present” is not “data correct”
Automation depends on sensors operating within calibration and environmental limits. Salt ingress, vibration, thermal cycling, and ageing cause drift long before outright failure. A drifting sensor feeds plausible but wrong data into control logic, leading to confident but incorrect system responses.
Automation is only as good as the most misleading sensor.
Professional ETO mindset
A competent ETO asks:
- Which alarms actually matter in the first 30 seconds?
- What data is assumed trustworthy — and why?
- What happens if the network slows, not fails?
- Can this system degrade gracefully, or does it collapse into noise?
Automation should reduce cognitive load, not increase it.
Knowledge to Carry Forward
Automation failures rarely look like crashes. They look like confusion. When control systems overwhelm crews with information at the wrong moment, the ship loses time — and time is what prevents escalation.
Design and maintain automation for clarity under stress, not completeness in calm.
Tags
ETO, Marine Automation, PLC Ships, SCADA Marine, Alarm Management, IEC 60092, IACS E10, Viking Sky