Rising coolant temperature on a harbour crossing
At 10:15 the coolant temperature alarm on the single 220 kW diesel engine of an 18 m passenger launch sounds at 98°C and the gauge is still rising. The launch is mid-crossing in Victoria Harbour with 60 passengers, calm water and heavy cross-traffic. The sea-water outlet is discharging weakly, the exhaust is slightly dark, and there is no unusual mechanical noise. The master calls the engine room asking whether to continue to the next pier, about six minutes away, or stop. The next scheduled trip is in 20 minutes and the company expects the timetable to be kept. The operator is alone, with a basic tool kit, an infrared thermometer and one spare raw-water pump impeller. No mechanic is available for at least an hour. The engine is the only prime mover and there is no auxiliary generator running.
1. State the immediate actions you would take in the first five minutes and explain your order of priority.
Read the worked answer
Priority order: people and vessel control first, machinery second. Inform the bridge immediately so the master can slow down, warn traffic and prepare passengers; do not create a blackout in a crowded harbour by stopping instantly unless there is smoke or a mechanical scream. Reduce load to idle or neutral to cut heat input while keeping steering and electrical supply, then investigate. Check the raw-water strainer and sea suction, pump belt and impeller, outlet flow, and coolant level (never open a hot cap). Use the infrared thermometer on the manifold and elbows. If outlet flow is weak and the strainer is choked, isolate it, clean it and restart the sea-water pump. Record times and temperatures throughout.
2. The temperature falls after you clear a plastic bag from the sea-water strainer. Decide whether to continue the trip and state the conditions you would impose.
Read the worked answer
Clearing the strainer proves the likely cause but not that the engine is fit to complete the timetable. Reload in small steps and watch the temperature for several minutes at manoeuvring load; confirm strong outlet flow and normal exhaust colour. If the temperature stabilises below the alarm and there is no steam or leak, proceed to the nearest pier at reduced speed, inform the master, and keep the engineer on watch with the alarm tested. If it climbs again, or outlet flow remains poor, stop in a safe position and arrange assistance. The decision is based on the trend under load, not one good reading. Passenger safety and traffic density outweigh the next scheduled trip.
3. What would you record and report, and why does it matter for the vessel's next watch?
Read the worked answer
Record the alarm time, temperature at alarm and during recovery, load changes, strainer debris, impeller condition, coolant topped up, and any temporary limits. Enter the defect in the engine log and brief the relief operator: the sea-water system has just choked, so the strainer must be checked frequently until the cause is removed. Report to the owner or company as a machinery defect and, if the vessel was delayed or endangered, follow the local reporting procedure. These records support maintenance planning and show that the watchkeeper monitored the defect rather than simply resetting an alarm.