Bergen B33:45 Medium-Speed Four-Stroke Engine

The Bergen B33:45 is the most recent generation of a Norwegian marine engine line that has run continuously since the 1940s. Rolls-Royce introduced it in 2014 as a diesel engine offering 600 kW per cylinder, which it described as the highest per-cylinder output in the 330 mm bore class at the time of launch. The gas version followed in 2018. The engine is built at Hordvikneset on the Hordvik peninsula, and since 31 December 2021 the Bergen Engines business has been owned by the UK private engineering group Langley Holdings, after the Norwegian government blocked an earlier sale to a Russian buyer on national-security grounds. The B33:45 is concentrated in the offshore-supply, fishing, cruise, ferry, and floating-production segments, where its long stroke and high torque per litre of displacement suit direct-drive and geared propulsion at low shaft speed.

Lineage from B32:40 to B33:45

The Bergen B-series traces to Bergens Mekaniske Verksteder, the Bergen mechanical works founded in 1855, which began building marine diesel engines in the first half of the 20th century. The line passed through Bergen Diesel, then Ulstein Bergen after the Ulstein group absorbed it, then Vickers, and into Rolls-Royce Marine when Rolls-Royce acquired Vickers in 1999. The immediate predecessor to the B33:45 is the B32:40, a 320 mm bore by 400 mm stroke medium-speed engine that ran in large numbers across the Norwegian and European fishing and offshore fleets through the 1990s and 2000s.

The B33:45 designation follows the Bergen convention of bore-colon-stroke in centimeters: 33 cm bore (330 mm) and 45 cm stroke (450 mm). The step from the B32:40 to the B33:45 raised the bore by 10 mm and the stroke by 50 mm, which lifted the swept volume per cylinder from roughly 32 liters to 38.5 liters and the per-cylinder rating from the B32:40’s level to 600 kW. The longer stroke is the defining design choice: it pushes the stroke-to-bore ratio to 1.36, well above the 1.0 to 1.2 range typical of the medium-speed segment, and trades peak rotational speed for torque.

Rolls-Royce designed the engine around a single stated priority. The 2014 launch document records that the design “was developed after consultation with a broad range of operators to establish what qualities they prize in an engine,” and that “the clear answer was life-cycle costs.” The five design targets that followed were lowest fuel and emissions, highest power per cylinder in the class, low life-cycle cost, a load-dependent maintenance schedule, and full equipment health monitoring. The result was a modular B-series platform built to share components across inline, vee, diesel, and gas variants from one parts pool.

Bergen Engines ownership: Rolls-Royce, the blocked TMH sale, Langley Holdings

The Bergen brand changed hands three times in two decades, and the most consequential transfer was a sale that did not happen. Rolls-Royce had held Bergen Engines since the 1999 Vickers acquisition and ran it within Rolls-Royce Power Systems. In February 2021, Rolls-Royce announced an agreement to sell Bergen Engines to TMH International, the Swiss-registered arm of Russia’s Transmashholding, the largest manufacturer of rail equipment in Russia. The headline value was around 150 million euros.

The Norwegian government stopped the deal. On 23 March 2021, Justice Minister Monica Maeland announced that the sale was blocked under Norway’s security legislation, on the basis that the engine technology and the Hordvik facility would be of military-strategic value to Russia and would increase Russian military potential. It was the first time Norway had blocked a transaction on national-security grounds, a point the International Bar Association recorded in its analysis of the decision. The block landed weeks before Russia’s full-scale invasion of Ukraine reshaped European views on Russian acquisitions of dual-use industrial assets.

Rolls-Royce then sold to a different buyer. On 3 August 2021 it signed an agreement with Langley Holdings plc, the privately owned UK engineering group, and the deal completed on 31 December 2021. Langley reported the enterprise value at 63 million euros and the final consideration at 91 million euros, well below the blocked TMH figure. Langley operates Bergen Engines alongside its Piller power-protection and Claudius Peters process-equipment businesses, and runs the brand as an independent unit from its Norwegian base. Kongsberg Maritime is the exclusive distributor of Bergen medium-speed engines for commercial marine applications, which places the B33:45 inside the Kongsberg integrated-vessel offering for Norwegian and export newbuilds.

Engine architecture

The B33:45 keeps the trunk-piston four-stroke layout that has defined the medium-speed segment since the 1970s, with the mechanical detail that a 600 kW-per-cylinder rating at a 26 bar peak mean effective pressure demands.

Crankcase, block, and crankshaft

The engine block is a one-piece casting carrying underslung main bearings, designed for low structural noise and vibration. Rolls-Royce stated at launch that the block design “ensures very low levels of vibration,” a property that matters for the offshore-supply, seismic-survey, and cruise applications where accommodation noise limits are tight. The crankshaft is forged and runs in main bearings sized for the firing loads at full BMEP. Full power can be taken from either end of the crankshaft up to and including the V12 version, which gives naval-architect freedom in arranging the engine relative to a gearbox or generator without a dedicated power-take-off design for each layout.

Cylinder units and the three-piece connecting rod

The B33:45 is built around complete cylinder units, each comprising the head, liner, piston, and connecting rod as a section that can be drawn and replaced as a unit. A three-piece connecting rod lets a piston be withdrawn without lifting the cylinder head, which shortens the overhaul time for piston-and-liner work. Rolls-Royce specified a piston-withdrawal height of 2,520 mm in the engine-room layout, a figure the installation designer uses to set the clearance under the engine-room crane. The cylinder-section design supports a pool-exchange service model, where overhauled heads and injection components are swapped in from a shared pool rather than reconditioned in place during the port call.

Fuel injection

The diesel B33:45 uses high-pressure injection at 1,800 bar, arranged to limit fuel-oil dilution of the lube oil system. The 1,800 bar injection pressure puts the engine in the modern high-pressure-injection band that supports the fine atomization needed for low particulate and low specific fuel consumption on residual fuel. The engine is designed for heavy fuel oil with a viscosity up to 700 cSt at 50 degrees Celsius, the ISO 8217 RMH 700 grade, and it also runs on marine diesel oil, marine gas oil, and low-sulfur fuels. Bergen rates specific fuel oil consumption against MDO with a net calorific value of 42.7 MJ/kg.

The current data-sheet SFOC runs from 171 g/kWh on the L9 to 174 g/kWh on the L8 at the best point, with the 2014 launch figure of 177 g/kWh at full load and 175 g/kWh at 85 percent MCR. Converting 173 g/kWh on MDO at a 42.7 MJ/kg net calorific value gives a brake thermal efficiency near 48.7 percent, which the SFOC to brake thermal efficiency calculator computes directly. Rolls-Royce stated at launch that the engines run “economical down to very low loads, without visible smoke,” a property that matters for the dynamic-positioning and harbor-maneuvering duty where the engine spends time well below its best-point load.

Turbocharging, charge-air cooling, and variable valve timing

The B33:45 uses two-stage charge-air cooling to manage the intake-air density across the load range, and variable valve timing to shape the effective compression and the air mass trapped in the cylinder at part load. Variable valve timing allows a Miller-type early inlet-valve-closing strategy, which lowers peak combustion temperature and the thermal NOx that forms with it, without giving up the geometric expansion ratio. The combination of high-pressure injection, two-stage charge-air cooling, and variable valve timing is what lets the diesel B33:45 meet IMO Tier II without exhaust after-treatment. For deeper background on the role of the turbocharger in a medium-speed engine, see the marine engine turbocharging reference.

Ratings, configurations, and dimensions

The B33:45 holds a constant 600 kW per cylinder across the marine inline range, which makes the total output a simple multiple of the cylinder count. The data-sheet figures below are from the Bergen B33:45L propulsion and generating-set technical data and the 2014 Rolls-Royce launch document.

The two BMEP values pair with the two rated speeds: 26 bar at 720 rpm for 60 Hz generator drive and 25 bar at 750 rpm for 50 Hz drive and for propulsion. As a propulsion engine running on the propeller law, the B33:45 operates from 450 to 750 rpm, which lets it match a fixed-pitch propeller curve down to part load without leaving the certified envelope. The marine rating is 600 kW per cylinder at both 720 and 750 rpm; the land power-generation rating is lower at 540 kW per cylinder at 750 rpm, reflecting the longer continuous-duty derating that base-load and prime-power stationary plants require.

The brake mean effective pressure is the figure that ties the per-cylinder power to the displacement and the speed, and it is the number that places the B33:45 against its competitors on equal terms. The 26 bar peak at 720 rpm reflects the firing-load capacity that Bergen designed into the running gear, the bearings, and the one-piece block. A 38.5 liter cylinder turning at 720 rpm and developing 600 kW puts the engine near the top of the naturally-fired medium-speed band, where pushing higher demands either a higher peak cylinder pressure or a richer charge, both of which cost engine life or emissions margin.

The mean piston speed is the single number that most directly characterizes a reciprocating engine’s mechanical duty, and the B33:45 data sheet reports it as 11.25 m/s. It sets the inertia loads on the running gear, the rubbing speed at the piston rings and the liner, and the practical ceiling on rotational speed for a given stroke. The 11.25 m/s figure follows directly from the 450 mm stroke at 750 rpm, and it sits near the top of the 9-to-12 m/s band that defines the medium-speed segment. The long stroke is what holds the rated rotational speed down: a shorter-stroke engine reaching the same power would have to spin faster, raising the mean piston speed past the ring-reliability ceiling near 10 m/s that governs liner and ring wear.

Pushing the rated speed higher to lift power would raise the mean piston speed past the practical wear ceiling, which is why Bergen holds the rating at 600 kW per cylinder rather than spinning the engine faster. The figure is a screening number rather than a design limit on its own; the peak piston speed, which occurs near mid-stroke, is roughly 1.6 times the mean and governs the inertia-load and lubrication analysis that sizes the running gear.

The inline engines were the first into production, with the V12 following as the launch document promised, and the vee range extending to V16 and V20 for the land power-generation market. Bergen has noted potential V10 and V14 variants. Specific lubricating oil consumption is 0.5 g/kWh across the range, and the engine-outlet cooling-water temperature is 90 degrees Celsius. Engine ratings follow ISO 3046/1 at a 45 degrees Celsius maximum ambient air temperature and a 32 degrees Celsius maximum seawater temperature, the tropical reference condition that governs the installed cooling-system design.

A 9-cylinder inline B33:45 at 5,400 kW weighs 56,400 kg dry, which works out to roughly 10.4 kg per kilowatt of rated power. That power density sits the engine in the normal medium-speed band, heavier per kilowatt than a high-speed engine such as the MTU Series 4000 or Caterpillar 3500 but far lighter than a slow-speed two-stroke of the same output. The companion medium-speed auxiliary engine genset calculator sizes a B33:45 genset’s electrical output from the mechanical rating, the alternator efficiency, and the power factor.

Fuel flexibility and the B33:45LG gas and dual-fuel variants

The B33:45 ships in two combustion families that share the block, the running gear, and most of the parts pool: the diesel engine and the gas engine. Rolls-Royce launched the diesel in 2014 and added the gas version in 2018, and the modular design lets an operator convert from diesel to gas and back through Bergen’s B3X engine platform. That convertibility is a commercial argument for owners with installed-base modernization programs: the engine that runs on marine diesel today can move to gas without a full replacement when the bunker economics or the regulatory exposure shift.

The gas engine, designated in the B33:45LG and vee-gas variants, runs in the lean-burn Otto cycle. It admits natural gas at low pressure to the inlet manifold during the intake stroke and ignites the lean gas-air mixture with a small diesel pilot injection at top dead center. The lean-burn Otto cycle keeps combustion temperature and the thermal NOx that forms with it low enough to meet IMO Tier III without after-treatment, which is the principal emissions advantage of a gas engine over a diesel that needs selective catalytic reduction to reach the same limit inside an emission control area.

The lean-burn Otto cycle carries a known trade-off: methane slip. Some unburned natural gas passes through the engine and exits in the exhaust, and methane is a far stronger greenhouse gas than carbon dioxide over the relevant accounting horizon. The slip erodes part of the greenhouse-gas benefit of switching from heavy fuel oil to natural gas, and the engineering response is in the gas-admission timing, the combustion-chamber geometry, and the piston-ring pack rather than in any single fix. This trade-off is general to the low-pressure dual-fuel medium-speed segment and is shared by the Wartsila 50DF and the equivalent MAN gas engines.

The diesel B33:45 also runs on biofuels in addition to the residual and distillate fuels noted above, which gives a partial route to lower lifecycle carbon without a gas conversion. The combination of a high-pressure-injection diesel that accepts biofuels and a gas variant that meets Tier III natively gives the platform two distinct decarbonization paths from one engine family.

Emissions compliance: NOx Tier II and Tier III

The B33:45 is certified against MARPOL Annex VI Regulation 13, which caps nitrogen-oxide emissions from marine diesel engines as a function of the engine’s rated speed. The diesel engine meets Tier II globally without after-treatment, and reaches Tier III inside designated emission control areas with selective catalytic reduction fitted. The gas engine meets Tier III natively through its lean-burn combustion. Rolls-Royce validated NOx levels within IMO limits across the 10 to 100 percent load range during the development program, with an SCR system included as part of that program and the SCR control unit integrated into the engine controller.

For the B33:45 at its rated speeds, the Regulation 13 limits fall in the 130-to-1999 rpm band, where the tier limits are speed-dependent rather than flat:

At 750 rpm the Tier II ceiling is 9.60 g/kWh and the Tier III ceiling is 2.39 g/kWh, a reduction of about 75 percent. The diesel B33:45 clears Tier II through combustion control: high-pressure injection, two-stage charge-air cooling, and Miller-type variable valve timing together hold the in-cylinder NOx formation below the limit. Closing the gap from Tier II to Tier III, the further 75 percent reduction, requires either the SCR after-treatment on the diesel or the switch to the lean-burn gas engine.

Selective catalytic reduction works by injecting a 32.5 percent aqueous urea solution into the exhaust upstream of a vanadium-tungsten-titanium catalyst bed, where the urea decomposes to ammonia and the ammonia reacts with the NOx to produce nitrogen and water vapor. Urea consumption on a medium-speed engine runs at a few percent of the fuel mass, and the urea tank, dosing system, and reactor add installed cost and engine-room volume. That overhead is one reason an owner with heavy ECA exposure may choose the gas engine, which meets Tier III without the SCR train. For the wider regulatory frame, see the NOx Tier I, II, and III reference and the marine auxiliary engines and generators overview.

Applications

The B33:45 is concentrated in the vessel types where the Bergen line has been strong for decades, and in selected global cruise and floating-production references. The same engine serves as mechanical-drive propulsion and as a generating-set prime mover, which is why a single platform covers main propulsion, diesel-electric power, and stationary generation.

In the offshore-supply sector, the B33:45 powers anchor-handler tug-supply vessels, platform-supply vessels, subsea-construction vessels, pipe-layers and heavy-lift ships, and seismic-survey vessels. These vessels run diesel-electric power plants where several gensets feed a common busbar that supplies the propulsion thrusters, the dynamic-positioning system, and the deck machinery. The low structural noise and the fast load response that Rolls-Royce designed into the engine matter for the dynamic-positioning duty, where the gensets must absorb step changes in thruster demand without tripping.

In the fishing fleet, the B33:45 is at the upper end of the world’s largest tuna seiners, longliners, and trawlers, a market the Bergen line has historically held in Norway, Spain, and the major distant-water fishing nations. Fishing vessels favor the long-stroke high-torque character because it matches a large slow-turning propeller, and the Norwegian proximity of the Hordvik works and the service network is a practical advantage for a fleet that returns to Northern European ports.

In passenger shipping, the B33:45 powers RoPax and ferry main propulsion, often in the Norwegian and Mediterranean coastal services, and it appears in cruise-vessel integrated power plants where it has displaced earlier Bergen and competitor engines on selected newbuilds. The engine also serves FPSO main power generation in North Sea, Brazilian, and West African operations, and stationary base-load and peaking power plants, where the V16 and V20 land engines extend the range into the tens of megawatts. The auxiliary engine load factor calculator estimates the operating load on a B33:45 genset from the connected demand, and the speed-power cubic fit calculator relates a propulsion B33:45’s power to vessel speed along the propeller law.

The cargo-ship and drill-ship references in the launch list extend the same diesel-electric pattern. A drill ship carries a large connected electrical load for the drawworks, the mud pumps, and the dynamic-positioning thrusters, and runs a multi-engine power plant where the engines are loaded and shed to track the drilling-operation demand. The 600 kW per-cylinder rating lets a designer hit a target installed power with fewer cylinders than a lower-output competitor, which Rolls-Royce listed as a launch benefit: “fewer cylinders with lower weight and cost.” For a six-engine FPSO plant the difference between a 600 kW and a 500 kW per-cylinder engine is several cylinders of maintenance scope across the fleet life. The land V16 and V20 engines carry the platform into prime-power and continuous-duty generation where the rating drops to 540 kW per cylinder, the continuous derating that base-load duty requires against the marine 600 kW intermittent rating.

Maintenance and operating characteristics

Bergen built the B33:45 around a maintenance model the company calls dynamic service intervals: up to 25,000 hours between main services when the engine operates within a defined load window. That figure is the headline maintenance claim and the basis for the low life-cycle-cost positioning. The interval is load-dependent rather than fixed, so an engine run consistently inside its design load window reaches the longer interval, while one cycled hard or run at sustained low load reaches a service earlier. Full equipment health monitoring feeds the maintenance scheduling, which moves the overhaul decision from a calendar-and-hours rule toward a condition-based one.

The complete-cylinder-unit construction and the three-piece connecting rod shape the on-board maintenance routine. A piston-and-liner job is done by drawing the piston without lifting the head, which cuts the crane operations and the time the cylinder is open. The pool-exchange model, where overhauled heads and injection components come from a shared pool and the removed parts go back for reconditioning ashore, keeps the port-call downtime short and moves the bench work off the vessel. For an engineering officer, the relevant on-board checks are the per-cylinder exhaust temperatures, the firing pressures, the lube-oil condition, and the charge-air and cooling-water temperatures, the same condition signals that feed the health-monitoring system.

Bergen Engines supports the B33:45 through service centers in Norway, the UK, the US, Brazil, and Singapore, with authorized service agents in additional ports and 24/7 support through the global network. The parts and service footprint is smaller than the MAN PrimeServ or the Wartsila Lifecycle networks, but the closeness to the Norwegian fishing and offshore-supply customer base remains a real strength for the fleets that operate from Northern Europe. Engineering officers joining a B33:45-powered vessel for the first time work to the same medium-speed watchkeeping discipline covered in the medium-speed four-stroke marine engines overview and the broader marine diesel engine reference.

Comparison with competing medium-speed engines

The B33:45 competes principally against the Wartsila 32, the Wartsila 31, and the MAN 32/40 in the 300-to-350 mm bore class, with the Korean HiMSEN H35 and the Japanese builders such as Hanshin and Akasaka present in regional markets.

The B33:45’s distinguishing feature is the 1.36 stroke-to-bore ratio, longer than the Wartsila 32 and the MAN 32/40 and close to the Wartsila 31, which yields high torque per unit displacement and supports operation at lower shaft speed in geared and direct-drive installations. The Wartsila 31 holds the Guinness World Record for the most efficient four-stroke diesel and has a thermal-efficiency edge at the design point; the B33:45 answers with high torque density, the 600 kW per-cylinder rating that Rolls-Royce claimed as a class lead at launch, and the convertibility between diesel and gas across one parts pool. Selection between the platforms turns on the vessel type, the service-network fit, and the fuel strategy rather than on a headline efficiency number, where the differences are small. The marine engine model decoder covers the naming conventions for Bergen, Wartsila, MAN, and the other makers in one reference.

Reconciling the published ratings with the engine geometry

The two cards above define the mean piston speed and the brake mean effective pressure in general terms; applied to the B33:45’s published data, both reproduce the data-sheet figures, which is what confirms the numbers are internally consistent rather than rounded.

Mean piston speed is the time-average linear speed of the piston, twice the stroke times the rotational speed. At the 750 rpm rating the 450 mm stroke gives $c_m = 2 \times 0.450 \times 750 / 60 = 11.25$ m/s, exactly the data-sheet value, and the result is independent of connecting-rod length because it averages over the full cycle. The 11.25 m/s sits near the top of the 9 to 12 m/s band that defines the medium-speed segment, a direct consequence of the long stroke: a shorter-stroke engine reaching the same power would spin faster and push the rubbing speed at the rings and liner past the wear ceiling, which is why Bergen holds the rating at 600 kW per cylinder rather than lifting the speed. The peak piston speed near mid-stroke runs about 1.6 times the mean and is the figure that sizes the running gear, so the mean is a screening number, not a design limit on its own.

Brake mean effective pressure normalizes power against displacement and speed so engines of different size compare on equal terms. The swept volume of one cylinder is $V_s = \frac{\pi}{4} D^2 L = \frac{\pi}{4}(0.330)^2(0.450) = 0.0385\ \text{m}^3$. For the 9-cylinder engine at 5,400 kW and 750 rpm, a four-stroke firing once every two revolutions gives $p_{me} = \frac{P \times 60 \times 2}{V_s\,z\,n} = \frac{5{,}400{,}000 \times 120}{0.0385 \times 9 \times 750} = 2.50 \times 10^6$ Pa, or 25.0 bar, matching the data sheet. The 6-cylinder engine at 3,600 kW and 720 rpm returns 26.0 bar, the figure paired with the 60 Hz generator rating. The factor of two is specific to the four-stroke cycle; carrying it onto a two-stroke engine doubles the apparent BMEP, and any cross-maker BMEP comparison first has to confirm each engine is quoted on the same rating basis, here ISO 3046/1 at the 45 and 32 degrees Celsius tropical reference.

The same speed-dependent arithmetic fixes the NOx ceilings. MARPOL Annex VI Regulation 13 sets the Tier II limit in the 130-to-1999 rpm band as $44 \times n^{-0.23}$ and the Tier III limit as $9 \times n^{-0.20}$; at 750 rpm these give 9.60 and 2.39 g/kWh, the values in the emissions table above, and the 75 percent step between them is the gap that the SCR train on the diesel or the lean-burn gas engine has to close.

Limitations

This article describes the B33:45 from the published Bergen Engines and Rolls-Royce technical data and the public record of the ownership changes. Several caveats apply for anyone using it for a procurement or installation decision.

The data-sheet figures are nominal ratings under the ISO 3046/1 tropical reference condition. The achievable continuous rating for a specific vessel depends on the actual ambient and seawater temperatures, the back-pressure of the exhaust and after-treatment system, the fuel grade, and the duty cycle, and Bergen specifies the project rating subject to the application. The SFOC figures (from 171 to 174 g/kWh on MDO at 42.7 MJ/kg, depending on configuration and load) are best-point values and do not represent the in-service average across a real operating profile.

The gas-engine and dual-fuel detail here is at the platform level. The exact per-cylinder gas-mode rating, the methane-slip figure, and the fuel-mode-switching procedure for a specific B33:45LG installation come from the project guide for that engine and the EIAPP certificate, not from a general reference. The V14, V16, and V20 ratings are noted from the launch document and the land-engine range; confirm the current per-cylinder figures for those configurations against the live Bergen data sheet, since the company states that data may change with continuous development. The competitor figures in the comparison table are approximate and are intended to place the B33:45 in its class, not to settle a head-to-head specification contest, which depends on the exact variant and rating of each engine.

See also

• Wartsila 32: medium-speed four-stroke marine engine: the nearest-bore Wartsila competitor
• Wartsila 31: medium-speed four-stroke marine engine: the efficiency-record holder in the class
• MAN 32/40: medium-speed four-stroke marine engine: the principal MAN competitor in the bore class
• Wartsila 50DF: dual-fuel medium-speed marine engine: a larger low-pressure dual-fuel reference
• Medium-speed four-stroke marine engines: overview: segment-level context across makers
• Marine auxiliary engines and generators: the genset role the B33:45 fills
• NOx Tier I, II, and III: the MARPOL Annex VI Regulation 13 framework
• Selective catalytic reduction: the Tier III after-treatment path for the diesel engine
• Marine engine model decoder: naming-convention reference across makers

Related calculators

• Marine Engine Model Decoder: parse a B33:45 designation
• Mean Piston Speed: reproduce the 11.25 m/s figure
• System - Auxiliary Engine: Medium-speed 4-stroke: size a B33:45 genset
• Engine - Thermal Efficiency from SFOC: convert SFOC to brake thermal efficiency
• Auxiliary Engine Load Factor: estimate genset operating load
• Speed-Power Cubic Fit: relate propulsion power to vessel speed
• MARPOL Annex VI: CII rating by year: operational carbon-intensity grade