Bearing temperature measurements are a critical part of machinery condition monitoring. However, experience shows that they should always be considered alongside other monitoring systems and inspection findings, as a recent case demonstrates.

Crew burn injuries and vessel damage

Last year, a bearing failure on a container vessel caused rapid heat generation, oil mist formation, crankcase overpressure and machinery damage. A crew member suffered serious burn injuries in the incident, and the vessel had to be towed from the North Atlantic to Freeport, Bahamas, for repairs.

The immediate cause was identified as the failure of the aft bearing on the upper intermediate gear. The bearing shell failure led to metal-on-metal contact and rotation of the bearing shell within the gear bearing housing. As the shell rotated, it closed the oil inlet bore, cutting off lubrication to the bearing. With no oil supply, the excessive friction generated heat, creating a hotspot and ultimately catastrophic bearing damage.

The heat development created a flammable oil mist in the upper crankcase, an area not protected by oil mist detectors. When the mist ignited, the resulting crankcase overpressure activated the crankcase relief valves. Eighteen engine-room doors buckled and were displaced from their hinges.

Normal readings right before

The incident developed extremely quickly. Alarms for an abnormal oil mist detector reading, main-engine slowdown, engine-room fire and activation of the local firefighting system were all recorded within just four seconds. Before this, the engine's standard pressure and temperature readings had remained normal.

This detail is significant because it shows that a localised bearing failure can escalate into a major incident before conventional monitoring systems provide any clear warning. Standard engine monitoring typically tracks system-wide parameters, such as lubricating-oil pressure and temperature at a limited number of measurement points. Because these are bulk readings, a localised hotspot in a single bearing can remain invisible until the damage is already severe, which is a recognised limitation of conventional parameter monitoring on large two-stroke and gear-driven machinery.

The subsequent investigation found no evidence of poor maintenance, oil contamination or restricted oil supply. The oil bores and piping were clear, and oil samples were within acceptable limits. Misalignment was also ruled out, and wear on the gear teeth was normal. Damage was limited to the aft gear bearing, while the other bearings served by the same lubrication system were unaffected. The absence of any identifiable root cause beyond the bearing shell failure itself underlines that even well-maintained machinery with acceptable oil condition can suffer this type of failure.

Recommendations

The case highlights the limits of conventional engine parameter monitoring. Effective condition monitoring should combine additional temperature measurement trends with information from oil mist detectors, lubrication systems, vibration monitoring, alignment checks and physical inspections. Bearing condition monitoring based on trends, rather than single absolute alarm limits, is particularly valuable because a slow rise in temperature at one point can be significant even when the reading is still within nominal range.

The maritime industry is increasingly introducing enhanced bearing-monitoring systems. These can measure additional bearing temperatures in real time and trigger alarms, automatic load reduction or engine shutdown when abnormal temperatures or trends are detected. Such systems can help prevent overheating, engine damage and costly downtime. For operators weighing such investments, this case illustrates the potential cost of the alternative: a towing operation across the North Atlantic, extensive machinery damage and serious crew injury resulting from a single bearing failure.

Where monitoring data is available, it should be retained together with timestamps, engine load, rpm, lubricating-oil pressure and temperature, alarm history and other relevant sensor data. This information may prove important both for identifying warning signs and for investigating an incident.

The key lesson is that bearing temperature monitoring is essential but not sufficient on its own. Even normal engine readings do not rule out a localised bearing failure. The most effective approach combines temperature trends with other monitoring data, physical inspections and manufacturer guidance, ensuring that any warning signs are acted upon quickly.

Source: Gard,