Answer
Immediate action
Inform Master and bridge and request reduction of RPM/load.
Identify the affected unit from symptoms such as:
Jacket cooling-water loss or abnormal expansion-tank level.
High/abnormal cylinder cooling-water outlet temperature.
Water from indicator cock/scavenge drains.
Abnormal exhaust temperature or combustion.
If serious leakage is suspected, stop the engine as soon as navigationally safe.
Do not restart until the possibility of water entering the cylinder has been checked because of hydraulic-lock/water-hammer risk.
Confirm the crack and extent
Open indicator cock and turn engine on turning gear; check for water.
Inspect liner through scavenge ports.
Check piston, rings, liner surface and scavenge space for water/rust marks.
Pressure-test the jacket cooling-water side if required.
Determine whether the crack is:
Internal/combustion-space crack, or
External/jacket-side crack, and whether it is actively leaking.
If spare liner is available
Safest permanent action is to renew the cylinder liner according to maker's procedure.
Inspect associated components—piston/rings, cylinder cover, stuffing box, cooling-water spaces and landing/sealing surfaces.
Renew liner O-rings/seals.
Check liner protrusion and clearances as specified by maker.
Pressure-test the cooling space before closing up.
If liner cannot be renewed immediately
Consult company technical management and engine maker/Class as applicable.
A cracked liner should not simply be welded or patched and returned to normal service unless an approved repair procedure specifically permits it.
If the damage makes the unit unsafe, prepare for unit cut-out/isolation, but only according to the engine maker's instructions.
For a crosshead two-stroke engine, this may involve fuel cut-out and other measures specified by the maker; the exact arrangement depends on whether the piston/connecting components can safely remain in operation.
Operate at restricted RPM/load only within maker-approved limits and monitor the remaining units carefully.
Before restarting
Ensure no water remains above the piston.
Blow through with indicator cocks open.
Check crankcase/scavenge space for water contamination.
Check system cooling-water pressure and level.
Start at minimum RPM and gradually increase load while monitoring: JCW temperature/pressure, exhaust temperature, scavenge temperature, piston cooling, bearing temperatures and leakage.
CE management actions
Notify Master, superintendent/company and Class/Flag where required.
Raise defect report and record relevant parameters/trends.
Investigate root cause: thermal stress, overheating, poor cooling, scale/deposits, corrosion/cavitation, incorrect liner fitting, O-ring/sealing problems, material/fatigue defect, or abnormal combustion.
Record repair, measurements and tests in PMS/engine records and arrange permanent repair at the earliest opportunity.