Slow steaming is operating the engine well below its maximum continuous rating (MCR), typically at 40 to 60 percent of MCR, to save fuel. Before and during slow steaming:

1. The engine should be operated within the manufacturer's recommended minimum load/speed band for continuous running; de-rating/load-limit the engine appropriately; ensure the turbocharger is kept off surge and the scavenge pressure is adequate.
2. Cylinder lubrication: adopt a low-load feed rate (electronic two-level lubrication) to avoid over-lubrication and deposit build-up; feed rates should be matched to load, not kept at sea-going rates.
3. Keep fuel viscosity/temperature correct: in slow steaming the fuel oil heater and viscosity control must be monitored; maintain fuel temperature to give the correct viscosity at the injector to ensure good atomization.
4. Maintain sufficient charge air pressure and scavenge pressure; monitor turbocharger speed and the air side for fouling (lambda/surge margin); keep the charge air cooler clean and water temperature high enough to give good air density.
5. Monitor exhaust temperatures, particularly the turbocharger inlet and individual cylinder exhaust temperatures, to detect over-loading of the turbocharger or its frequent operation in the low-efficiency range - no abnormal build of carbon.
6. Manage the cooling water temperatures: keep jacket water at specified high temperature to limit corrosion and reduce thermal stress; maintain scavenge air temperature above the dew point of the combustion gases to reduce acid corrosion.
7. Check sealing and lubricating of the cylinder, and keep liner wall temperature high enough (lagging and insulating of the scavenge space) to prevent cold corrosion.
8. Confirm all safety and protection systems are operative, alarms set, and that turning gear/procedures for manoeuvring remain available; ensure air system pressures are adequate.

• Cold corrosion: low liner/gas temperatures allow sulphuric acid to condense on the liner, causing corrosion wear.
• Over-lubrication at constant high feed rate leads to carbon and ash deposits in ring grooves, on the piston crown and in the scavenge space, and can cause stuck rings, liner polishing and scavenge fires.
• Turbocharger matching/tailure: single turbocharger may run in surge or at low efficiency, reducing scavenge pressure and causing poor combustion, soot and higher specific consumption; exhaust gas temperature drops.
• Reduced exhaust gas temperature may cause boiler/economiser efficiency problems and corrosion in the waste heat system.
• Deposits build up in exhaust valves and turbocharger, increasing maintenance intervals; some components (exhaust valves, fuel injection, piston rings) are prone to increased wear or fouling from running at low load for a long time.

Before returning:

• Overhaul/clean as necessary the turbocharger (air side), exhaust valves, scavenge space (if deposits), and check piston rings/crown - bring injectors and components to good condition.
• Re-adjust cylinder lubrication feed rate back to full-load setting; check oil feed and clearances.
• Gradually increase the load (in steps) so that temperatures and thermal stresses build up slowly; ensure exhaust temperatures rise evenly and turbocharger accelerates to normal speed; allow time at intermediate loads so the engine and turbocharger reach equilibrium and to burn off deposits by the higher gas temperatures.

After:

• Confirm all temperatures, pressures, ratios normal and no abnormal noise/vibration; settle the engine at MCR/appropriate service load;
• Rese-turbed procedures; carry out a round of checks (exhaust temperatures, exhaust gas against baseline) and confirm the plant runs efficiently; update logs.