The vessel in question has 4 eight cylinder medium speed engines of 200mm bore as its generating plant. Each generator has its own engine driven cooling water pump and the four systems use a common expansion tank.
The vessel blacked out after number 3 generator tripped on a low lub oil pressure alarm. The generator would not restart. Investigation found the sump full of water and the expansion tank empty. The tests on the other engines found that the sump oil had negligible water content. On filling the expansion tank and opening up the cooling to No 3 generator, water was found leaking badly from one of the units into the crankcase.
On removing the cylinder head, the full extent of the damage was revealed. The valves had broken off/melted leaving all the stems in place. Part of the head had melted/burnt through. The piston crown had melted, cracked and had a hole burnt through it.
Further investigation found damage to crankshaft journals and bearings due to the water in the lubricating oil. The turbocharger nozzles and rotor suffered extensive damage due to pieces of valve passing through them. Due to overheating/ water in lubricating oil, all unit liners were suffering from microsiezure and scoring of varying severity.
The Expansion tank low level alarm was found to be OOO, as was the cooling water outlet high temperature alarm on the engine in question. The engines were not fitted with a cooling water low pressure alarm. Although the Main engine was subject to LO testing for water, the generators were not.
It is amazing that the engine kept running for so long, and that the watchkeeper didn't notice anything amiss (the engine room was manned) such as noise, vibration etc.