MAN 48/60: Large-Bore Medium-Speed Marine Engine

The MAN 48/60 is the largest engine in MAN Energy Solutions’ medium-speed four-stroke trunk-piston programme, with a 480 mm bore and 600 mm stroke. It produces 1,200 kW per cylinder at 500 rpm and is offered from L6 through V18, covering an output band of approximately 7,200 kW to 21,600 kW. The engine powers the main propulsion and generation plants of the world’s largest cruise ships, FPSOs, and naval vessels.

The current production version is the 48/60CR, carrying full common-rail fuel injection at up to 1,800 bar. Its predecessor, the 48/60B, used electronically controlled mechanical injection and remains in service on many vessels built before the early 2000s. Both variants share the same bore, stroke, and cylinder geometry; the CR designation signals the injection architecture that separates them.

For quantitative analysis of the 48/60CR’s rated output across cylinder configurations, the MAN ES V48/60B - MCR per Cylinder calculator on this site provides configuration-by-configuration power figures. The companion Engine - Thermal Efficiency calculator can convert published SFOC values to brake thermal efficiency for direct comparison with competing engines in the same bore class.

Engine family context

MAN Energy Solutions’ medium-speed four-stroke programme spans roughly 1 MW to 22 MW per engine. The MAN L21/31 at the lower end and the MAN L32/44CR in the middle address auxiliary genset and modest propulsion markets; the 48/60 sits at the top of the in-line and V-configuration portfolio. The 51/60DF dual-fuel engine shares the same 600 mm stroke and crankshaft spacing and is the gas-capable sibling at 510 mm bore, deployed where IMO Tier III compliance in gas mode replaces the need for SCR on the diesel platform.

Above 22 MW, shipowners switch to slow-speed two-stroke engines or multiple medium-speed units in diesel-electric or mechanical parallel arrangements. The 48/60 in a four-engine or six-engine cluster often reaches 60 MW to 90 MW of installed capacity, which is the typical power plant of a large cruise ship. No four-stroke trunk-piston competitor from Wärtsilä or Bergen reaches the same per-cylinder output at 480 mm bore in current production.

The MAN Energy Solutions corporate history traces the 48/60 lineage to the large-bore engines developed in Augsburg and Frederikshavn from the 1980s onward. The engine is a product of Holeby Diesel and MAN B&W lineage consolidated under the MAN Energy Solutions brand after the acquisition of the Holeby works.

Cylinder geometry and thermodynamic ratings

The 48/60CR’s 480 mm bore and 600 mm stroke give it a swept volume of 108.5 litres per cylinder and a stroke-to-bore ratio of 1.25:1, which places it in the moderate long-stroke class for a medium-speed engine. A stroke-to-bore ratio above 1.0 favours fuel economy over engine compactness: piston mean speed at 500 rpm works out to 10.0 m/s, low enough for long piston-ring and cylinder-liner life while the large bore area provides ample space for the four-valve head and the large-bore injector nozzles of the common-rail system.

The rated brake mean effective pressure (BMEP) in the 48/60CR is approximately 25 bar to 26 bar at ISO conditions, a number that has increased progressively from the 48/60A’s 21 bar in the late 1980s through the 48/60B’s 24 bar in the 1990s. Each step was enabled by improvements in turbocharger pressure ratio (the engine uses high-efficiency single-stage turbochargers supplied by Accelleron, formerly ABB Turbo Systems, and by MAN’s own TCA series), combustion chamber geometry, and valve and piston-crown material specification.

The 1,200 kW per cylinder rating at 500 rpm translates to a specific power of approximately 11.1 kW per litre of displacement per cylinder. This is not exceptional by high-speed diesel standards, but it is high for an engine intended for heavy-fuel-oil service at a bore size where thermal loading and ring-pack durability are the binding constraints, not peak power density.

At 514 rpm (the alternative speed used in some 60 Hz power-generation variants), the output per cylinder rises marginally due to the higher engine speed; total installed capacity in a V18 at 514 rpm reaches approximately 22,000 kW. Most marine propulsion installations use the 500 rpm rating for direct coupling to a controllable-pitch propeller or a gearbox driving a fixed-pitch propeller, while power-generation variants drive 50 Hz or 60 Hz alternators through a gearbox or at direct frequency.

Cylinder configurations and installed power

The in-line configurations (L6 through L9) are the standard choice for direct mechanical propulsion where engine room length is not a constraint and the parallel crankshaft layout simplifies installation in monohull vessels. The V configurations (V12 through V18) are selected when maximum power is needed from a compact engine room footprint, as in cruise ships where the usable engine room volume is taken by hotel plant and the propulsion machinery competes for space with diesel-electric switchboards, gearboxes, and shaft lines.

A V18 at 21,600 kW is approximately 15 m long, 5.5 m wide, and 6.5 m tall, weighing around 350 tonnes complete. Four of these installed in a large cruise ship provide 86,400 kW of installed generation capacity before any emergency or harbour generators are counted. Most large cruise ships use six to eight medium-speed units in various cylinder counts rather than four V18s, to maintain power availability when any one unit is offline for maintenance.

Common-rail injection: the 48/60CR system

The 48/60CR’s common-rail system decouples injection pressure generation from engine speed. In a mechanically injected engine, the fuel pump delivers pressure proportional to camshaft speed, which means injection pressure at low engine loads is far below the optimal level for good atomisation. Common-rail fixes pressure at a set rail level, typically 1,600 to 1,800 bar across the operating range, regardless of engine load or speed.

On the 48/60CR, a high-pressure fuel pump driven from the engine camshaft charges a common accumulator rail. Electronically controlled injectors at each cylinder draw from this rail. The engine control system sets injection timing, duration, and rail pressure independently for each cylinder. This enables:

• Rate shaping: the injection event can begin with a short pilot quantity before the main charge, reducing the rate of pressure rise in the cylinder and lowering combustion noise. On conventional mechanically injected engines, rate shaping requires complex jerk-pump timing mechanisms.
• Multiple injections per cycle: pilot, main, and post-injection events can be sequenced within a single combustion stroke. Post-injection is used to oxidise soot in the cylinder rather than letting it accumulate on piston crowns and liners.
• Load-independent pressure: at 20% load, where a mechanical pump might deliver 600 to 800 bar, the CR system maintains 1,400 to 1,600 bar. The improvement in spray atomisation at light load is measurable in reduced SFOC and black-smoke reduction.
• Cylinder-by-cylinder balancing: if one cylinder runs slightly hotter or shows higher combustion noise, the control system can trim its injection timing without adjustment of other cylinders, which isn’t possible on cam-timed mechanically injected engines without individual pump shimming.

The 48/60CR predecessor, the 48/60B, used MAN’s own electronically controlled mechanical injection (ECMI) system, which retained the jerk pump but moved injection timing control from a mechanical governor to an electronic actuator on the pump rack. The ECMI system is more reliable in contaminated fuel conditions than full common-rail, because high-pressure accumulator systems are sensitive to water or abrasive contamination in the fuel at 1,800 bar. The trade-off is that ECMI cannot match the CR system’s part-load efficiency or its emissions control capability at IMO Tier II and III NOx targets.

48/60B versus 48/60CR: comparison

Design and engineering detail

Turbocharging

The 48/60CR uses a single-stage high-efficiency turbocharger on each bank (one per bank for V-configurations, one for in-line configurations). Accelleron’s A-series turbochargers and MAN’s own TCA series are the standard fitments, with pressure ratios of approximately 4.5:1 at full load. The high pressure ratio requires charge air cooling to keep the manifold temperature within acceptable limits for cylinder filling and NOx control; a two-stage charge air cooler (high-temperature and low-temperature stages) is standard.

The turbocharger operates at speeds up to 23,000 rpm on a floating bearing. Exhaust gas bypassing through a waste gate is not used on the 48/60 platform; instead, the turbine is sized for a firing load at which the compressor delivers the correct boost throughout the load range. Variable turbine geometry (VTG), which MAN uses on smaller engines such as the L32/44CR, is not fitted to the 48/60CR in current production; the large turbine rotor diameter at this bore size makes VTG mechanically complex.

Combustion chamber

The 48/60CR’s combustion chamber is shaped by a slightly domed piston crown with a shallow toroidal bowl, four valves (two intake, two exhaust), and a centrally mounted common-rail injector. Four valves per cylinder improve breathing at the large bore diameter: with only two valves, the valve curtain area at maximum lift limits volumetric efficiency. Valve seats are Stellite-faced for heavy-fuel-oil resistance to vanadium-sodium hot corrosion, which attacks softer seat materials at the exhaust valve temperature of approximately 500 degrees C.

Cylinder liners are centrifugally cast alloy cast iron with a plateau-honed bore surface. Bore polishing from sulphuric acid attack is controlled by alkaline cylinder lubrication, with base-number lubricant matched to fuel sulphur content as required by MARPOL Annex VI Reg. 14 sulphur cap compliance oils and the specific gravity of the fuel.

Crankshaft and main bearings

The crankshaft is forged steel with fillets rolled for fatigue resistance. Main and crankpin bearing journals on the 48/60CR are substantially oversized relative to the bore class (journal diameter approximately 460 mm for main bearings), providing a generous oil-film safety margin at the 1,200 kW per cylinder thermal load. Bearing shell material is lead-bronze or aluminium-tin alloy depending on engine serial number and service history; MAN has progressively moved toward aluminium-tin overlays that do not require lead-based overlays for corrosion resistance.

The marine engine crankshaft and main bearings article on this site covers the inspection and wear assessment methods that apply to the 48/60 family in the context of scheduled overhaul planning.

Valve train and camshaft

The 48/60CR retains a traditional camshaft-driven valve train: a single camshaft per bank, gear-driven from the crankshaft, actuating intake and exhaust valves through pushrods, rocker arms, and hydraulic lash adjusters. Common-rail injection removes fuel pump cams from the camshaft, which historically occupied a large fraction of camshaft length on jerk-pump engines. The freed camshaft real estate allows larger base circles on valve cam lobes, reducing contact stress and extending cam lobe life between overhauls.

Exhaust valves rotate via a Rotocap mechanism on each valve stem. Rotation distributes the vanadium deposit load around the valve face and seat rather than concentrating it at a fixed angular position, extending valve life in heavy fuel oil service by a factor measured in thousands of hours.

Fuel capability

The 48/60CR runs on ISO 8217 heavy fuel oil up to RMG 700 (700 cSt at 50 degrees C) as its design fuel, without derating. This is the standard high-sulphur heavy residual fuel of the bunker market. Heating the fuel to approximately 130 to 145 degrees C before the engine fuel system reduces viscosity to the 15 to 20 cSt injection-ready range.

Low-sulphur heavy fuel oil (LSHFO), marine diesel oil (MDO), marine gas oil (MGO), and VLSFO (0.50% sulphur, in compliance with the MARPOL Annex VI Reg. 14 global cap in force from 1 January 2020) are all compatible without hardware modification. Switching from HFO to distillate fuels requires flushing the fuel system to avoid co-mixing of residual and distillate fuel, which can cause compatibility precipitation in fuel filters and injectors.

The heavy fuel oil article on this site describes the ISO 8217 grade categories, ignition quality measurement (CCAI), and the compatibility testing methods used when changing fuel batches on medium-speed engines including the 48/60.

Biofuels and drop-in alternatives

MAN Energy Solutions has published compatibility guidance for FAME (fatty acid methyl ester) blends up to B30 (30% FAME, 70% fossil fuel) on the 48/60CR, subject to fuel elastomer compatibility review and enhanced water separation. Hydrotreated vegetable oil (HVO) is compatible without blend limits on the 48/60CR’s fuel system, because HVO has paraffinic rather than ester chemistry and causes no elastomer swelling.

Straight methanol or ammonia operation requires hardware that does not exist on the 48/60CR platform as of 2026; this is the application space of the separate 51/60DF (LNG, methanol variants) and the in-development ammonia variants. MAN announced a methanol-ready 48/60 concept in 2024 and an ammonia-ready version in 2025, but these are designated future products rather than production engines.

Emissions: IMO Tier II and Tier III

The 48/60CR meets IMO Tier II NOx limits as built on all current ratings. IMO Tier II imposes a NOx limit of approximately 9.8 g/kWh for engines at 500 rpm under the NOx Technical Code 2008 (NTC 2008) test cycle E3 or E2 for propulsion engines. The 48/60CR achieves Tier II through combustion optimisation: delayed injection timing, optimised charge air temperature, and common-rail rate shaping reduce peak combustion temperature and therefore thermal NOx formation.

IMO Tier III, which tightens the NOx limit to approximately 2.0 g/kWh in NOx Emission Control Areas (ECAs) designated by IMO under MARPOL Annex VI Reg. 13, requires a reduction of approximately 80% from the Tier II level. The 48/60CR does not reach Tier III through engine design alone; it requires a selective catalytic reduction (SCR) system installed downstream of the turbocharger in the exhaust line.

The selective catalytic reduction article explains the SCR operating principles; on the 48/60CR, the exhaust temperature at the SCR inlet is typically 280 to 380 degrees C at normal load, within the optimal window for urea (AdBlue) decomposition and NO-to-N2 conversion over the vanadium-based catalyst. SCR systems on the 48/60 are sized to handle the full exhaust volume of a V18 at maximum load, which is a substantial unit: catalyst volume on a V18 SCR is typically 15 to 25 cubic metres.

MARPOL Annex VI Reg. 13 NOx Tier rules and the engine’s certification under NTC 2008 determine whether SCR is mandatory based on the vessel’s build date, keelaying date, and trading area. Cruise ships keel-laid from 1 January 2016 onward operating in Tier III ECAs require SCR or an equivalent approved technology; most modern cruise ships with the 48/60CR carry SCR systems on each engine.

Selective catalytic reduction on the 48/60 does not affect main engine power output or specific fuel oil consumption. The back-pressure added by the SCR catalyst and exhaust ducting is compensated by turbocharger tuning at the installation design stage.

NOx limits by tier (500 rpm engines)

Note: the exact limit for Tier II at 500 rpm is calculated from the IMO formula n^0.2 * 44 / (n + 1.96) applied at n = 500, giving 9.82 g/kWh. Tier III in ECAs is approximately 80% below Tier II.

Applications: cruise ships

The diesel-electric cruise ship is the 48/60’s dominant application. A large cruise ship (above 100,000 gross tonnes, which covers the majority of ships built since 2000) typically installs four to six medium-speed engines in an integrated electric propulsion plant. The engines drive synchronous generators; the electrical output feeds azimuthing pod propulsors (such as ABB Azipod or Rolls-Royce Mermaid units), bow thrusters, and all hotel loads from a common shipboard electric grid.

In this architecture, the engine room does not contain a traditional main shaft or gearbox connecting the engines to the propellers. The flexibility of electric propulsion allows engines to be started and stopped to match the power demand at any instant, which is particularly valuable for a cruise ship where hotel loads (HVAC, galleys, entertainment systems, elevators) account for 50% to 60% of total power consumption at sea and nearly all of it in port.

Royal Caribbean’s Oasis-class ships (Oasis of the Seas, Allure of the Seas, and subsequent sisters built from 2009 onward), each above 225,000 GT, use three MAN 48/60CR diesel-electric power plants alongside two Bergen-type engines, generating a total installed capacity above 90 MW. MSC Meraviglia (2017, 171,598 GT) and Carnival’s Vista-class vessels similarly use MAN 48/60CR engines as primary generation plant.

The choice of the 48/60 for cruise ships follows from three attributes: the V18 delivers 21,600 kW from a single crankshaft, which is hard to match at this bore class; the common-rail system’s part-load efficiency is valuable because cruise ships frequently operate at reduced generation loads during overnight port calls; and the engine’s long overhaul intervals (up to 24,000 hours between major top-end overhauls on current ratings) suit the operating pattern of cruise vessels that need continuous commercial availability.

Applications: FPSO power generation

Floating production, storage, and offloading vessels (FPSOs) need large, reliable diesel or dual-fuel generating sets to power the topsides processing plant and the vessel’s own systems. The FPSO floating production storage offloading article covers the vessel type in detail; for power generation, the 48/60CR competes with slow-speed two-stroke generators (which are unusual in this application due to their physical height) and gas turbines (which are preferred when associated gas is available and cheap).

FPSO installations on the Brazilian pre-salt fields, West African deepwater, and the Norwegian continental shelf frequently use multiple 48/60 units providing 30 MW to 60 MW of firm generation capacity. The engine’s heavy-fuel-oil tolerance is valuable on FPSOs that burn crude oil-derived fuels or asphaltenic slop fractions that are unacceptable to gas turbines. In-line configurations (L6 through L9) are often preferred on FPSOs because the narrower footprint fits within the modular topsides weight constraints better than V-configuration engines.

Applications: naval vessels

The 48/60 family has been adopted in several naval programmes, primarily for large platform vessels, replenishment ships, and amphibious assault vessels rather than for high-speed combatants. Naval vessels require high specific power in confined spaces, long endurance, and tolerance of variable operational tempos; the 48/60’s 1,200 kW per cylinder output and the availability of power takeoff flanges for frequency conversion and shaft motor integration make it suitable for CODLAG (Combined Diesel-Electric and Gas) and IEP (Integrated Electric Propulsion) configurations.

The French MISTRAL-class amphibious assault ships (LHD, built at DCNS/Naval Group yards, commissioned 2006 and 2007) use two 48/60CR engines in a diesel-electric plant alongside gas turbine boost units. The Italian Navy’s Cavour aircraft carrier (launched 2004, commissioned 2008) uses a similar integrated electric propulsion arrangement with four-stroke medium-speed engines from the same bore class.

Naval engine variants of the 48/60 are typically specified with enhanced seakeeping provisions: shock-mounted engine foundations, redundant lube-oil cooling circuits, and fuel system modifications to handle fuel contamination during replenishment-at-sea operations. MAN certifies naval 48/60 variants against MIL-STD shock requirements and relevant national naval standards.

Engine variants across the 48/60 generation

48/60A (early production)

The original 48/60A, produced from the late 1980s, used conventional mechanical jerk-pump injection with a pneumatic governor. BMEP was approximately 21 bar. In-line configurations L4 through L9 and V12 were the primary offerings. The engine established the 480 mm bore platform and defined the cylinder spacing and crankshaft geometry that subsequent variants retained.

48/60B

The 48/60B introduced electronic engine management and MAN’s ECMI (electronically controlled mechanical injection) system in the 1990s. BMEP rose to approximately 24 bar. Electronic control allowed more precise injection timing over the load range, improving fuel efficiency and lowering NOx to Tier I levels without derating. The 48/60B remains in service on vessels built from the mid-1990s through the early 2000s; MAN PrimeServ supports the variant with genuine and approved parts from the Augsburg and Frederikshavn stores.

48/60CR (current production)

The 48/60CR replaced the 48/60B in new orders from approximately 2002 onward. Common-rail injection raised BMEP to approximately 25 to 26 bar, improved part-load SFOC by 5 to 8% relative to the 48/60B, and enabled the emission tuning needed for IMO Tier II compliance without derating. The V18 configuration reaching 21,600 kW was introduced on the 48/60CR platform; the 48/60B’s largest V-configuration offered somewhat lower per-cylinder output.

The 48/60CR is the current production standard as of 2026, with the 51/60DF (510 mm bore, 600 mm stroke) as the dual-fuel complement for vessels prioritising LNG operation and Tier III compliance in gas mode without SCR.

Portfolio context: where the 48/60 fits

MAN Energy Solutions’ medium-speed four-stroke programme at 500 to 750 rpm covers the following bore classes in current production:

The gap between the L32/44CR (up to 11 MW) and the 48/60CR (from 7.2 MW) reflects a deliberate market segmentation: the 48/60CR’s 7.2 MW minimum output in L6 configuration already exceeds the L32/44CR’s maximum V20, so there is no bore-class overlap; a shipowner needing 6 MW selects the L32/44CR V12 or V14, while a shipowner needing 8 MW selects the 48/60CR L7.

MAN does not offer a medium-speed four-stroke in the 35 mm to 45 mm bore range at 500 rpm for marine applications in current production (the L35/44DF at 720/750 rpm fills a different speed-specific niche); the 48/60 therefore stands as MAN’s answer to any propulsion requirement between 7.2 MW and 21.6 MW per shaft.

Lifecycle, overhauls, and PrimeServ support

MAN Energy Solutions operates the 48/60 under a structured maintenance programme with defined time-based inspection and overhaul intervals. The following intervals apply to the 48/60CR in standard HFO service; distillate-fuel operation can extend top-end intervals by 10 to 15%.

Typical intervals on the 48/60CR:

• Cylinder head and valve inspection: 8,000 hours
• Full top-end overhaul (pistons, rings, liners): 16,000 to 24,000 hours depending on fuel sulphur and service history
• Crankshaft bearing inspection: 32,000 hours or as indicated by bearing wear debris analysis
• Turbocharger major overhaul (Accelleron A-series or MAN TCA): 25,000 to 30,000 hours
• Major engine overhaul: 60,000 hours or 20 years, whichever is first

The V18 configuration weighs approximately 350 tonnes complete (engine only, excluding gearbox, mounting system, and cooling equipment). Major overhauls require specialist lifting equipment; engine rooms on cruise ships and FPSOs are designed at build with removal routes for cylinder heads and piston assemblies that allow maintenance without drydocking.

MAN PrimeServ supports the 48/60 family from dedicated large-engine depots in Augsburg (Germany), Frederikshavn (Denmark), Copenhagen (Denmark), Singapore, Houston (USA), and facilities in Busan, Shanghai, and other major port cities. PrimeServ Assist provides remote condition monitoring via onboard sensors and data transmission, allowing Augsburg engineers to review combustion and vibration signatures between port calls. Genuine MAN parts for the 48/60 are stocked with a quoted delivery lead time of 24 to 48 hours for critical components from the main depots.

The marine engine performance monitoring article describes the combustion analysis and indicator card methods that apply to the 48/60CR in routine service, including the use of electronic cylinder pressure indicators that MAN integrates with PrimeServ Assist’s onboard data acquisition.

Turbocharging and charge air system

The marine engine turbocharging article on this site covers the principles; for the 48/60CR, the turbocharger arrangement is noteworthy in its simplicity relative to the engine’s output level. A single high-flow turbocharger per bank (or a single unit on in-line configurations) handles the full exhaust energy of up to nine cylinders (on an L9) or nine cylinders per bank (V18 uses two units). The pressure ratio of approximately 4.5:1 is achievable with a single-stage design on the 48/60CR because the engine speed is low (500 rpm) and the exhaust pulse energy per cylinder is large, making pulse turbocharging efficient.

Charge air cooling follows a standard two-stage arrangement: high-temperature stage (HT cooler) removes heat using engine jacket water at approximately 85 degrees C; low-temperature stage (LT cooler) uses seawater or central cooling water at approximately 32 to 36 degrees C for the final cooling to target manifold temperatures of 40 to 60 degrees C depending on ambient conditions and NOx tuning requirements. Higher manifold temperature raises combustion temperature and NOx; lower manifold temperature improves charge density and fuel efficiency.

Fuel injection system maintenance

Common-rail injectors on the 48/60CR are precision components manufactured to tolerances of a few micrometres. Fuel cleanliness is more critical than on mechanically injected engines: the standard fuel treatment chain includes centrifugal separators (typically two in parallel at full throughput), fine mesh filters to 10 micrometres, and water-in-fuel monitoring. ISO 8217 fuel grade F-RMG 700 permits significant particulate contamination that, if not removed, attacks injector needle seats and rail valve seating surfaces.

Injectors are exchanged on a pool basis during routine overhauls rather than bench-tested on the vessel. MAN PrimeServ maintains injector test benches at the main depots and can supply exchange injectors on 24-hour delivery to any port served by the main logistics network. The standard injector overhaul interval on the 48/60CR is approximately 8,000 to 12,000 hours, consistent with the cylinder-head inspection interval.

The marine engine fuel injection systems article covers common-rail injector design, the high-pressure pump architecture, and the failure modes that service engineers encounter across medium-speed engines in this bore class.

Engine control system

The 48/60CR uses MAN’s own SaCoS engine control system (Safety and Control System). SaCoS manages:

• Injection timing and duration at each cylinder
• Rail pressure setpoint and high-pressure pump output
• Engine speed governor function (load-sharing when multiple units are paralleled)
• Overspeed, low lube-oil pressure, and high jacket-water temperature shutdowns
• Alarm logging and interface to the vessel’s integrated automation system (IAS)

SaCoS communicates with the IAS via standard fieldbus protocols (CANopen, Modbus, or PROFIBUS depending on installation). Cruise ships and FPSOs with MAN 48/60CR installations typically integrate SaCoS data into a centralised power management system (PMS) that automates engine start/stop sequencing based on load demand and redundancy requirements.

The marine engine room automation and monitoring article describes the IAS integration context and the condition monitoring signals that drive predictive maintenance on large four-stroke installations.

Comparison with competing engines

The MAN 48/60CR does not have a direct contemporary competitor from a single OEM at the same bore-stroke-speed combination. Wärtsilä’s largest medium-speed offering in current production is the Wärtsilä 46F at 460 mm bore, 580 mm stroke, 500 to 514 rpm, producing approximately 1,100 kW per cylinder; the Wärtsilä 46F article on this site covers its design and applications. The 46F’s maximum output in V16 configuration is approximately 17,600 kW, which is below the 48/60CR V18’s 21,600 kW.

Bergen Engines (Kongsberg) does not offer a bore equivalent to the 48/60 in current production; the B33:45 series at 330 mm bore addresses a lower power class. Caterpillar’s C280 and the EMD series do not reach the 48/60’s per-cylinder output in medium-speed diesel applications.

This competitive position means the 48/60CR is effectively the default choice for power requirements above 17 MW per unit in medium-speed four-stroke diesel service, unless the application specifies dual-fuel operation, which routes it toward the 51/60DF.

Limitations

The 48/60CR’s large bore and heavy construction impose real constraints that users need to assess before specifying the engine.

Engine weight and handling. A V18 at 350 tonnes is the heaviest medium-speed engine in MAN’s portfolio. Vessels designed to carry four to six of these units require detailed structural analysis of engine room double-bottom foundations. The crane capacity and removal routes for piston assemblies (each piston/rod assembly on a V18 weighs approximately 1.2 tonnes) must be designed into the vessel at the naval architecture stage; retrofitting a V18 into a space designed for smaller units is not commercially feasible.

Minimum load constraints. The 48/60CR’s optimal efficiency band is 75% to 100% of MCR. Below 40% load, thermal efficiency falls off more steeply than on smaller bore engines because the large cylinder volume creates higher heat loss per unit of fuel energy at low firing rates. Cruise ships operating at anchor or in port with low hotel loads often keep only one or two engines running at moderate load rather than running all units at very low load, which requires a load-balancing strategy in the PMS and appropriate switchboard configuration.

Fuel quality sensitivity. Despite tolerance of ISO 8217 heavy grades, the 48/60CR’s common-rail system is more sensitive to fuel water content and micro-contamination than mechanically injected predecessors. Centrifuge efficiency must be maintained to the maker’s specification. VLSFO compatibility requires compatibility testing when switching between batches, because VLSFO blends can form asphaltenic sludge when mixed with other residual fuels.

Spare parts lead time. While MAN PrimeServ holds critical components at multiple depots, major structural items such as crankshafts, cylinder blocks, and camshafts for the V18 are not stock items. A crankshaft replacement on a V18 requires advance manufacturing lead time that can exceed six to nine months for a custom forging. Operators in remote ports must plan major overhauls against depot proximity.

No IMO Tier III compliance without aftertreatment. Unlike dual-fuel engines such as the 51/60DF, which meets Tier III in gas mode without SCR, the 48/60CR cannot achieve Tier III through engine design modifications alone. Vessels committed to trading exclusively in Tier III NOx ECAs must install SCR on every 48/60CR unit, adding capital cost, urea consumption costs, and catalyst replacement intervals.

Technology maturity ceiling. The 48/60 platform has been in production for approximately 35 years. The thermodynamic ceiling on achievable BMEP at this bore class, assuming continued HFO compatibility and the mechanical constraints of trunk-piston construction, is approximately 28 bar. Further output increases are possible but require material upgrades to piston crowns, valve seats, and cylinder liners that may not be economically justified when the existing installed base operates reliably at current ratings.

See also

• MAN L32/44CR: Medium-Speed Four-Stroke Marine Engine
• MAN 32/40: Medium-Speed Four-Stroke Marine Engine
• MAN L21/31: Medium-Speed Four-Stroke Marine Engine
• MAN Energy Solutions: Corporate History
• Medium-Speed Four-Stroke Marine Engines
• Marine Engine Makers
• Wärtsilä 46F: Medium-Speed Four-Stroke Marine Engine
• Trunk Piston Engine Architecture
• Marine Engine Common-Rail Technology
• Selective Catalytic Reduction (SCR)
• Heavy Fuel Oil
• MARPOL Annex VI Reg. 13 NOx Tier Rules
• Marine Engine Turbocharging
• Marine Engine Fuel Injection Systems
• Marine Engine Performance Monitoring
• FPSO: Floating Production, Storage and Offloading

Calculators:

• MAN ES V48/60B - MCR per Cylinder
• MAN ES V51/60DF - MCR per Cylinder
• Engine - Thermal Efficiency
• Engine - Pcomp vs Pmax Ratio
• Mean Piston Speed
• System - Auxiliary Engine: Medium-speed 4-stroke
• Marine Engine Model Decoder