Answer
A Main Engine (M/E) main bearing high temperature alarm or trip is a critical emergency. Continued operation without taking specific isolation and protection steps will cause white metal wipe, crankpin/journal scoring, and potentially a catastrophic engine room fire or crankcase explosion.
Immediate Safety & Emergency Actions
- Inform Bridge & Reduce Load
- Immediately request the bridge to slow down the engine (Slow Ahead / Dead Slow Ahead). Reduce M/E load significantly to minimize peak combustion pressure (Pmax) and hydrodynamic load on the affected bearing.
- Do NOT Stop Engine Abruptly (If Running Safely at Reduced Speed)
- If the bearing temperature is steadily high but not rapidly skyrocketing past critical trip limits, keeping the engine turning slowly allows continuous oil flow to carry heat away. Stopping abruptly can cause "baking" or welding of white metal to the journal.
- If the temperature trips the engine or passes critical limits (e.g., >85°C–90°C), stop the engine immediately.
- Prevent Crankcase Explosion
- Do NOT open crankcase doors immediately after stopping or slowing down. Wait at least 20–30 minutes for hot spots to cool below the ignition temperature of oil mist.
- Verify Oil Mist Detector (OMD) readings and check bearing temperature sensors/thermocouples.
After stopping and observing crankcase-entry precautions, I will inspect the bearing and journal. I will check for wiped/melted white metal, scoring, bearing clearance, blocked LO drilling, damaged oil pipe, low LO pressure, water/dirt in oil, loose/incorrectly tightened bearing structure and misalignment. The maker also recommends inspecting the bearing shell and journal and, where running marks are abnormal, checking crankshaft deflection.
If there is no severe bearing damage, the temperature becomes stable, and maker/Class/company agree that restricted operation is acceptable, I will proceed to the nearest safe port at minimum safe RPM, avoiding barred/critical speed ranges. The engine room will remain continuously attended and I will closely monitor main-bearing temperature, LO pressure/temperature, oil mist, vibration, filter debris, crankshaft condition and the other main bearings.
if I have a spare main-bearing shell, I will stop and replace the damaged shell after confirming that the journal, saddle and crankshaft alignment are satisfactory and after removing the root cause. I will then pre-lubricate, turn on turning gear, start at minimum RPM and proceed to port under close monitoring. If the journal is damaged or the bearing housing is distorted, I will not simply fit the spare shell and run.
if the main bearing is genuinely damaged and no spare is onboard, I will stop and inspect it. Minor surface damage may only be dressed temporarily if permitted by the maker. If the shell is wiped, cracked or badly damaged, I will not run the engine merely to reach port. I will inform company, Class and maker, arrange the correct spare/technical assistance, and the vessel may require towage. A main bearing cannot be isolated like a cylinder unit.
If necessary, I may cut out the cylinder associated with that crank throw to reduce combustion/dynamic loading, To relieve combustion forces transmitted directly through the connecting rod to the affected main bearing, isolate (cut out) the cylinder unit(s) immediately adjacent to or supported by that bearing:
- Fuel Isolation:
- Conventional engines (MAN B&W MC / Sulzer RTA): Lift and latch the fuel pump roller guide or activate the puncture valve / cut-out lever to block fuel rack movement.
- Electronic engines (MAN ME / WinGD RT-flex): Cut out fuel injection for the target unit directly from the Main Operating Panel (MOP) or Engine Control System interface.
- Exhaust & Scavenge Management: Lock the fuel pump in zero position, shut off the fuel supply valve to the unit, and open the indicator cock to verify zero combustion pressure. Ensure the exhaust valve operates according to engine maker guidelines for isolated-unit operation.
- Cylinder Lubrication: Turn down the cylinder oil lubricator feed rate for the isolated cylinder to the minimum allowable setting (or per maker instructions) to avoid excessive unburned oil accumulation in the scavenge space.
Operating a 2-stroke engine with an isolated cylinder shifts its torsional vibration dynamics. Consult the vessel's Class-approved Torsional Vibration Calculation (TVC) manual for the "1-Unit Cut-Out" condition.
Barring / Restricted Speed: Pass through the altered critical RPM range rapidly. Do not run the engine continuously within this speed range.
Engine Load Limit: Limit maximum engine output to the maker-specified limit for 1-unit cut-out operation (typically 40% to 50% MCR).
Statutory & Classification Notification: Regulatory Compliance.
- Flag State & Class Notification: Operating with a wiped/damaged main bearing or an isolated unit constitutes a defect affecting vessel seaworthiness under MARPOL / SOLAS. Notify the Flag State Administration and Classification Society immediately.
- Single-Voyage Dispensation: Request permission from Class to proceed to the nearest port of repair under restricted engine load and single-unit isolation.
- Official Entries: Document all temperature logs, communications with Chief Engineer and Bridge, notifications sent to the Designated Person Ashore (DPA), and times of unit isolation in the Engine Room Logbook and Official Logbook.