Hull and machinery incident - Engine breakdown

The following incident occurred on a general cargo vessel.

RPM drop
When the incident occurred, the vessel was fully loaded and under way to a European port. The vessel was at sea, the main engine was running on full speed as normal and everything seemed to be as it should.

The engine crew only discovered that something was wrong when they noted that the main engine RPM had dropped and a bearing high temperature alarm had been activated.

Since the RPM had dropped and the main engine shaft generator was connected,  a blackout also occurred at this time. The auxiliary engines started automatically and electric power was restored. However, the main engine was still running and had to be stopped manually.

Checks
The engine crew did not open the crankcase doors, but only checked the temperature on the doors, which gave no indication of over-heating. The lube oil pressure also appeared normal. After ten minutes the chief engineer decided to start the main engine again and continue the journey.

The RPM was slowly increased to full speed and it was noted that bearing temperatures increased to in excess of the permissible upper limit before decreasing again. At the same time, several lube oil filter alarms sounded. This was found to be caused by sludging.

It was decided to continue at full speed, despite all bearing temperatures being above normal, several lube oil filter alarms having been recorded, and a persisting lube oil sludging problem. The vessel continued at this speed until a crankcase explosion occurred the next morning. An automatic shutdown of the main engine was activated by the oil mist detector which was followed by heavy smoke and the sounding of the fire alarm.

Investigation
Further investigation and subsequent dismantling of the components of the crankcase revealed substantial damage to the main and crank bearing. Several bearing shells were found to have been completely smashed or deformed. Furthermore, several pistons, including liners, were cracked. The engine crew quickly realised that they were unable to repair the engine and the master was informed that towing was necessary.

Upon arrival at the port, service engineers from the manufacturers attended on board and started dismantling the crankcase to facilitate further investigation. It quickly became clear that the crankshaft was bent and beyond repair. Due to the unavailability of spare parts and the consequent delivery time, repair time was estimated to be approximately 10 weeks.The investigation concluded that the most probable cause of the breakdown was the thin-walled white metal lining of one of the main bearings having broken and subsequently fallen into the crankcase. This again was the probable cause of the blocked  oil supply, which led to the damage.

The crankshaft then lost its support in way of the main bearing, and this, in the end, caused the crankshaft explosion. As  the crankshaft also had to be renewed, the repair time was quite extensive.

Lesson learned
In the end we have to ask, could something have been done to prevent or reduce the damage? As can be seen above, there were several indications beforehand that something was wrong. Also, when the first warning alarm sounded, the crankshaft doors were not opened to manually check the temperature.

The lube oil alarms and the persisting sludging problem were also ignored, which again could be an indication that something was wrong.

It also has to be mentioned that the engines were running in this condition for several hours before the explosion.

The end  result was very expensive for all involved, and it is strongly recommended that alarms or any indications that something is wrong are not ignored until you have satisfied yourself that everything is safe.