A general cargo vessel departed port after loading cargo where the crew was religiously carrying out the vessel departure routines. The main engine was tried out both in ahead and astern directions, all air bottles pumped up, and generators were kept standby. The vessel left the berth with the assistance of a single tug. The vessel was in complete command of the Captain and the crew, thereby the vessel was turned and all set to sail out within ten minutes. The tug line was released and within next ten minutes, there was a sudden blackout. The main propulsion engine came to a halt, thereby the Master ordered to drop both the anchors, nevertheless, the vessel came into contact with the harbor breakwater.
The company did investigate the reason for the sudden propulsion failure. It was found that the main engine shutdown was activated due to the alarm triggered by the crankcase oil mist detector.
You should be wondering – Why the crankcase oil mist alarm instead of slowing down the engine directly stopped it ? But, in this case, the particular model of the oil mist detector had only one mode – ie., when the alarm activates, it leads to direct stoppage of the main engine.
Please note:
Most designs of oil mist detector have two modes.
- Sea mode – where the oil mist detector alarm would directly shut down the main engine, as in this case, and
- Harbour mode – where the oil mist detector alarm would slow down the engine and thus the RPM is reduced, whereby the propulsion is still maintained to reach safety.
It is still worthy to understand why in the first place did the oil mist alarm activate?
The investigation found that in this case the OMD experienced a false alarm. While loading in port, the main engine stand-by heating had been switched off to allow maintenance, allowing a higher than normal humidity within the engine. The OMD detection was apparently triggered by the resulting water condensation.
Lessons learned
1. Although it is tempting to free harbour tugs as quickly as possible, in the restricted waters of a small port their assistance can be invaluable should something go wrong.
2. A well-designed safety device such as an OMD should have at least two operating modes to better mitigate risks.
3. When conditions are changed from normal operational values, such as in this case by shutting off the main engine stand-by heating, expect the unexpected. Take the time to think through whether any unwanted consequences may result.
Source: Nautical Institute – MARS report.
