High Exhaust Temperature and Turbocharger Surge After Aktau Bunkering
Your 8,900 GT product tanker is on passage from Aktau to Baku, 180 nautical miles, with a MAN B&W 6S50MC-C main engine. Six hours after bunkering 380 cSt fuel at Aktau, No. 4 unit exhaust gas temperature rises to 425 °C against 380 °C on the other units, and the turbocharger begins surging at about 70% load. Fuel pump index is higher than normal, scavenge drain has increased, and the fuel valve has not been overhauled for 4,000 hours. The supplier's analysis reports density 991.2 kg/m3 at 15 °C, water 0.65% by volume, viscosity 402 cSt at 50 °C, and Al+Si 42 mg/kg. The settling tank is held at 45 °C because the steam tracing is partly blocked; the purifier is running at maximum throughput. The master is under commercial pressure to maintain full sea speed and asks whether the engine can continue.
1. What is your diagnosis, and what immediate engine-room actions will you take before deciding whether to continue?
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The combination points first to poor fuel treatment and possible unit damage, not simply a faulty thermometer. Density 991.2 kg/m3 and water 0.65% exceed the RMG limits, and 45 °C settling temperature is too low for a 380 cSt fuel that probably has a high pour point. At maximum purifier throughput the separator cannot remove water and cat fines effectively, so the fuel valve and exhaust valve on No. 4 may be fouling or suffering abnormal combustion.
Immediate actions:
- Reduce main engine load to about 60% and stop the turbocharger surge by avoiding the affected load range; do not race the engine.
- Switch to the second fuel tank or distillate if available, and isolate the suspect tank from the service system.
- Raise settling tank temperature gradually to about 55–60 °C, provided the heating system is safe, and reduce purifier throughput to 30–40% of rated capacity. Drain water from settling and service tanks.
- Check the fuel valve, exhaust valve, scavenge spaces, and turbocharger for carbon or damage; compare exhaust temperatures and indicator diagrams across units.
- Increase monitoring of No. 4 exhaust temperature, scavenge drain, and turbocharger speed. If temperature continues to rise or surge persists, stop the engine and investigate before further running.
- Log all actions, retain fuel samples, and inform the master and company.
2. The charterer wants full sea speed to Baku. How do you decide whether to continue, reduce load, or stop, and whom do you notify?
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The decision is a risk assessment, not a commercial vote. Full sea speed is unacceptable while No. 4 is above its normal exhaust temperature and the turbocharger is surging, because a damaged exhaust valve or turbocharger can lead to piston seizure, scavenge fire, or loss of propulsion in confined waters.
A defensible plan is to continue at reduced load only if:
- No. 4 exhaust temperature stabilizes below the manufacturer's alarm limit;
- turbocharger surging stops;
- no abnormal vibration, smoke, or scavenge drain is observed;
- the engine can be controlled from the bridge and local control remains available.
If any of these conditions fails, stop the engine, anchor in a safe location, or drift clear of the traffic lane, and repair or change over the unit.
Notify the master immediately and recommend a reduced-speed passage. Inform the company and charterer through the master. Notify the flag State or class only if the defect affects the ship's seaworthiness or requires survey; in practice, a main engine deficiency that limits propulsion should be reported to the company and considered for class notification. Also inform the port of Baku if arrival is delayed or the ship cannot maintain manoeuvrability. Record the decision and the technical basis in the engine log and a letter of protest to the supplier.
3. What documentation and samples should you secure for the bunker dispute, and how should the fuel be managed on arrival?
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Secure the evidence chain immediately. Retain the supplier's sealed sample and the ship's continuous drip sample from the receiving line, plus samples from each settling tank and the service tank. Label them with date, time, tank, port, and seal numbers, and store them in a secure locker. Keep the bunker delivery note, certificate of quality, port State bunker receipt, and the chief engineer's letter of protest describing the observed density and water content.
Record in the engine log and oil record book, where applicable, the time of switching tanks, purifier settings, temperatures, exhaust temperatures, and any repairs. Take photographs of the sample seals and tank labels. Send a copy of the analysis to the company and charterer, and request a joint analysis by an independent laboratory if the supplier disputes the result.
On arrival, do not commingle the suspect fuel unnecessarily. Keep it segregated, continue to treat it slowly if it can be used safely, or retain it for shore disposal if it is off-specification. Before using it again, verify density, water, and compatibility with the remaining fuel. If the fuel is off-specification, the company should pursue a commercial claim and consider a request for tank cleaning or de-bunkering. Do not allow commercial pressure to override the engine manufacturer's fuel limits.