Cooling failure on a passenger launch approaching a typhoon shelter
At 21:40 a 22 m local passenger launch, powered by a single 6-cylinder 180 kW diesel engine, is proceeding at 1,200 rpm from Central to Cheung Chau with 48 passengers. The engine operator on watch notices the fresh water outlet temperature has risen from 82°C to 96°C in six minutes, the exhaust gas temperature on cylinder 6 is 510°C against 390°C on the others, and the raw water pressure gauge has dropped from 1.2 bar to 0.4 bar. No sea suction strainer differential pressure alarm is fitted. The bridge has just called for maximum speed to keep clear of a moving dredger. The engine room is hot at 42°C, the sea water pump is belt-driven, and the belt looks slack. The vessel is 0.8 nm from a typhoon shelter entrance.
1. What should the engine operator do in the first five minutes, and what must be reported to the bridge?
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Immediate actions
- Treat this as a sea water cooling failure until proved otherwise. Reduce load to slow speed, not necessarily stop, because the vessel is in a busy harbour and the bridge needs steerage. Inform the bridge at once that maximum speed is not available and why.
- Check the raw water overboard discharge, sea suction valve position, strainer, pump belt tension and pump impeller. A slack belt can slip at higher rpm, so tightening it or reducing rpm may restore flow. Do not open a sea strainer under pressure; close the suction, stop the pump, clean and reassemble.
- Monitor fresh water temperature, all exhaust gas temperatures, lube oil pressure and any abnormal noise. Do not open the hot coolant cap.
Report to bridge State the symptoms, the action taken, the maximum safe rpm and the fact that one cylinder is running hot. The bridge needs this to decide whether to keep clear of the dredger at reduced speed or enter the shelter.
Reasoning The falling raw water pressure with rising fresh water temperature points to the sea water side, not the fresh water side. The high exhaust gas temperature on cylinder 6 may be a separate injector or fuel issue, but cooling must be restored first. Continuing at 1,200 rpm risks piston seizure, exhaust fire and loss of the engine in a fairway.
2. The belt is tightened and raw water pressure returns to 1.0 bar, but the no. 6 exhaust gas temperature remains at 470°C while the others are about 400°C. The vessel is now 0.3 nm from the shelter. Decide whether to enter the shelter and stop, or continue to Cheung Chau, and state the conditions that would change your decision.
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Decision: enter the shelter and stop at a safe berth or anchor clear of the fairway.
The cooling problem is only partly corrected. A single cylinder at 470°C while the others are near 400°C suggests an injector, fuel pump or compression fault. If the injector is over-fuelling, the exhaust valve and piston crown can overheat; if it is under-fuelling, the cylinder may be washing lubrication from the liner. Either way, continuing a passenger trip at speed turns a manageable defect into a possible engine-room fire or a broken engine in open water.
Conditions that would allow a short reduced-load passage to a nearby berth
- Fresh water temperature stable below about 90°C and raw water pressure steady.
- No abnormal knocking, smoke or lube oil pressure drop.
- Exhaust gas temperature not rising further and below the engine maker's limit.
- A safe berth is close, weather is moderate and the bridge accepts reduced speed.
Even then, do not resume the passenger run. Inform the company, arrange a replacement vessel or engineer, and record the temperatures, pressures and actions in the engine room log. The safety of 48 passengers outweighs the commercial pressure to complete the trip.