Oil mist detector malfunction likely caused $3.4m collision

A false alarm from an oil mist detector was a significant factor in a collision in the Sabine Pass, Texas, in August 2022, which involved general cargo ship Damgracht (IMO 9420784) and bulk carrier AP Revelin (IMO 9694696).

The 18,143 dwt Netherlands-flagged Damgracht and the 38,795 dwt Croatian-flagged AP Revelin collided at about 10:45 local time on August 21st 2022, when the Damgracht, operated by Amsterdam-based Spliethoff’s Bevrachtings BV. was inbound in the Sabine Pass Outer Bar Channel en route to Beaumont, Texas. The AP Revelin, which was operated by Dubrovnik-based Atlanska Plovidba, was outbound.

The two vessels collided after the Damgracht lost propulsion. Its main engine shut down due to a high level of oil mist density sensed by its oil mist detector (OMD). The engine shaft-driven electrical power take-off generator, which had been powering the bow thruster, stopped producing power. The thruster then also stopped.

As a result of its sudden loss of propulsion, the Damgracht veered into the path of the AP Revelin. The pilot aboard the Damgracht took steps to notify and avoid the AP Revelin. However, the pilot did not have any way of manoeuvring the vessel, and as a result the Damgracht and the AP Revelin collided. No injuries were reported. However, the AP Revelin suffered some $3.4m-worth of damage.

​The day before the collision the Damgracht’s main engine had alarmed. Shortly after this it shut down due to a high cooling water temperature. That evening the engine crew cooled down the main engine and repaired a failed cylinder head gasket. It was thought that the gasket failure allowed cooling water to leak into the cylinder, thus contaminating the engine’s lube oil system. The work to repair it resulted in the interior sections of the engine being exposed to humid conditions.

That evening the humidity averaged about 90%. It was thought likely that higher levels of water entered the crankcase than could be removed overnight by the lube oil purifier, or could evaporate from the heat of the running engine in the short time that it was tested post-repair.

As a result, while the Damgracht was underway the following morning, the OMD triggered a false alarm after sensing water vapour that had condensed in the sample.

The National Transportation Safety Board (NTSB) determined that the probable cause of the collision between the two ships was the Damgracht’s loss of propulsion caused by an automatic shutdown of the main engine due to a false alarm, likely triggered by water vapor sensed by the oil mist detector shortly after engine maintenance was completed to replace a failed cylinder head gasket during high-humidity conditions.

The NTSB said that, when certain engine components fail, such as cylinder head gaskets, then cooling water could be introduced as a result into engine lube oil systems. High humidity or extreme cold temperatures could increase the water content within engine lube oil sumps. This consequent elevated quantity of water in lube oil systems could trigger false alarms in engine crankcase oil mist detectors – leading to an engine shutdown – due to water droplets passing through the measuring track or the filter glass detecting condensation. These water droplets could be mistaken for oil mist by the sensors.

The NTSB said therefore that, after an engine’s crankcase had been opened and exposed to these conditions during maintenance and repair, it would be good practice for engine crews to inspect and test the lubricating oil system for water intrusion and ensure lube oil purifying equipment was functioning properly, removing any water or other contamination in the lube oil.

NTSB investigators worked closely with its counterparts from Coast Guard Marine Safety Unit Port Arthur throughout this investigation