Bergen B33:45 Medium-Speed Four-Stroke Engine

The Bergen B33:45 is the current generation of a Norwegian marine engine line that has run since the 1940s. Rolls-Royce introduced it at the SMM trade fair in Hamburg in 2014 as a diesel engine offering 600 kW per cylinder, about 20 percent more per cylinder than the previous Bergen range, and described it as the most powerful engine in its 330 mm bore class. The engine is built at Hordvikneset on the Hordvik peninsula, north of Bergen. Since 31 December 2021 the Bergen Engines business has belonged to 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. It belongs to the medium-speed four-stroke segment, and the linked overview places it against the wider maker field.

Lineage from Bergen Mekaniske Verksted to the B33:45

The Bergen B-series traces to Bergen Mekaniske Verksted, the Bergen mechanical works founded in 1855 as a shipbuilding business. The works set up a diesel-engine division in 1942 and completed its first engine design in 1946. That division was spun off in 1984 as BMV Maskin, bought by the Ulstein group in 1985 and renamed Bergen Diesel, then passed to Vickers when Vickers absorbed Ulstein, 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 then stroke in centimeters: 33 cm bore (330 mm) and 45 cm stroke (450 mm). The step from the B32:40 raised the bore by 10 mm and the stroke by 50 mm, which lifted the swept volume per cylinder from about 32 liters to 38.5 liters and the per-cylinder rating to 600 kW. The longer stroke is the defining choice. It pushes the stroke-to-bore ratio to 1.36, above the 1.0 to 1.2 range typical of the medium-speed segment, and trades peak rotational speed for torque. The marine engine model decoder sets out the same bore-and-stroke convention across Bergen, Wartsila, MAN, and the other makers.

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 design targets that followed were the highest power per cylinder in the class, low fuel consumption and emissions, 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 builds from one parts pool. The engine draws on Bergen’s 30 years in the 3x cm bore class, the design heritage the company set out in its 2016 CIMAC Congress technical paper.

The Bergen engine family: C25:33, B32:40, and B33:45

The B33:45 is the largest and newest of the current Bergen range, which spans about 1.4 MW to 12 MW. The whole family uses the same bore-then-stroke naming in centimeters, and every platform pairs a liquid-fuel engine with a gas engine that shares its core. The smallest is the C25:33, a 250 mm bore by 330 mm stroke engine rated at 220 to 300 kW per cylinder in 5, 6, 7, 8, and 9-cylinder builds from 1,200 to 2,700 kW, used mainly for generating sets; its gas counterpart is the C26:33. Above it sits the established B32:40 at 320 by 400 mm, with the B35:40 gas engine at 350 mm bore. The B33:45 and its B36:45 gas engine top the range at 330 and 360 mm bore.

The modular B-series replaced the older Bergen K-series, which ran for decades in Norwegian fishing and coastal vessels. The switch traded the K-series design for a build that shares power packs and multifunctional components across inline and vee, diesel and gas, so a fleet running mixed Bergen engines carries a smaller spares pool. For an owner already operating a C-series genset alongside a B33:45 main engine, part of the service and training scope overlaps, which the single-family design is built to reward. The medium-speed four-stroke marine engines overview places this Bergen range next to the Wartsila, MAN, and HiMSEN families in the same bore class.

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 inside 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 maker of rail equipment in Russia. The reported value was about 150 million euros; some outlets put it near 180 million US dollars.

The Norwegian government stopped the deal. On 23 March 2021, Justice Minister Monica Maeland told parliament that the sale would be halted under the National Security Act section 2-5, and the King in Council formalized the block days later. The government cited the risk that the engine technology and the Hordvik facility would strengthen Russian military capacity, a concern sharpened by Bergen’s supply and service of engines on Norwegian naval and coast-guard vessels. 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. Bergen Engines was not even subject to the Security Act’s reporting duties, so the government invoked its broad discretionary power to intervene.

Rolls-Royce then sold to a different buyer. On 3 August 2021 it agreed terms with Langley Holdings plc, the privately owned UK engineering group, and the deal completed on 31 December 2021 for a consideration of 91 million euros, with a further 16 million euros of cash inside Bergen Engines AS retained by Rolls-Royce. The final figure sat well below the blocked TMH price. Langley reported that Bergen Engines generated revenues near 250 million euros and employed almost 950 people worldwide, more than 600 of them near Bergen. 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. That places the B33:45 outside the Rolls-Royce group, while the MTU high-speed engines covered in marine engine makers stay inside Rolls-Royce Power Systems.

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. The general layout, the firing order, and the running-gear discipline follow the pattern set out in the four-stroke marine diesel engine fundamentals reference.

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, which gives the 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 carrying 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 cuts the overhaul time for piston-and-liner work. The cylinder-section design supports a pool-exchange service model, where overhauled heads and injection components come from a shared pool rather than being reconditioned in place during the port call. The modular parts pool also carries multifunctional components across the inline and vee builds, which holds down the spares inventory an operator has to keep for a mixed fleet.

Fuel injection

The diesel B33:45 uses a pump-line-nozzle fuel system at 1,800 bar injection pressure, arranged to limit the number of connections and to prevent fuel-oil dilution of the lube-oil system. The 1,800 bar pressure puts the engine in the modern high-pressure 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 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, low-sulfur fuels, and biofuels. Bergen rates specific fuel oil consumption against MDO at a 42.7 MJ per kg net calorific value.

The current Bergen marine sheets give specific fuel oil consumption at MCR of 173 g/kWh on the L6, 174 on the L8 and 171 on the L9 without engine-driven pumps, rising to 175, 176 and 173 g/kWh with two engine-driven pumps fitted, all on that MDO reference. The 177 g/kWh at full load and 175 g/kWh at 85 percent MCR that the engine is usually quoted at are the 2014 Rolls-Royce launch figures. Converting 175 g/kWh at 42.7 MJ per kg gives a brake thermal efficiency near 48 percent, high for a naturally-fired medium-speed engine. Rolls-Royce stated at launch that the engines run “economical down to very low loads, without visible smoke,” which matters for the dynamic-positioning and harbor-maneuvering duty where the engine spends time well below its best-point load. The launch document flagged common-rail injection and two-stage turbocharging as later upgrade paths designed into the platform from the start.

Turbocharging, charge-air cooling, and variable valve timing

The B33:45 uses two-stage charge-air cooling to manage 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 mix 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 the role of the turbocharger in a medium-speed engine, see the marine engine turbocharging reference.

Cooling and reference conditions

The engine runs a jacket-cooling circuit to an outlet temperature of 90 degrees Celsius, with the two-stage charge-air cooler taking the compressed intake air down before it enters the cylinder. Ratings are quoted to ISO 3046/1 at a 45 degrees Celsius maximum air-intake temperature and a 32 degrees Celsius maximum seawater temperature, the tropical reference that sets the size of the installed radiators, box coolers, or central-cooling heat exchangers. A ship working colder water carries margin against that reference, so the derating an installation engineer applies depends on the route rather than on the nameplate alone. The 90 degrees Celsius jacket outlet also fixes the grade of waste heat available for a fuel-oil heater or a fresh-water generator, which the auxiliary-system design has to balance against the engine’s own cooling demand.

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 figures below come from the current Bergen marine data sheets (B33:45 in-line propulsion, B33:45 in-line generating set, and B33:45V generating set). The catalogue has moved since launch: the 2014 Rolls-Royce brochure and the B33:45 project guide list an L7 at 4,200 kW, and no current Bergen marine sheet does, so the L7 row below is the Rolls-Royce-era variant rather than a current offering.

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 on the propeller law, the B33:45 operates from 450 to 750 rpm, which lets it follow 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 continuous-duty derating that base-load and prime-power stationary plants require. On the generating-set data sheet the L6, L8, and L9 deliver about 3,160, 4,220, and 4,755 kW of electrical output at alternator efficiencies of 46.2 to 46.8 percent.

The brake mean effective pressure is the figure that ties the per-cylinder power to the displacement and the speed, and it places the B33:45 against its competitors on equal terms. The 26 bar peak at 720 rpm reflects the firing-load capacity 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 needs 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 at 750 rpm. 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 speed down: a shorter-stroke engine reaching the same power would spin faster, raising the mean piston speed past the ring-reliability ceiling near 10 m/s that governs liner and ring wear.

The inline engines were the first into production, with the V12 following as the launch document promised. The V16 is a marine engine, not a land-only one: Bergen’s marine generating-set sheet lists the B33:45V16A at 9,600 kW and the marine propulsion page the V16P at the same output, and only the V20, at 10,585 kW electrical, is confined to land power generation. Specific lubricating oil consumption is 0.5 g/kWh across the range.

The dry weight of the 6-cylinder L6, excluding the transport foundation, is 42,400 kg on the current Bergen propulsion data sheet (53,500 kg for the L8, 56,400 kg for the L9), which works out to about 11.8 kg per kilowatt of rated power. The 2014 Rolls-Royce brochure figure of 40,210 kg is the launch-edition weight. 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 the Caterpillar 3500 , but far lighter than a slow-speed two-stroke of the same output. In its genset role the B33:45 feeds a common busbar as one of the marine auxiliary engines and generators that supply a diesel-electric power plant.

The B36:45 gas engine and the B3X convertible platform

Rolls-Royce launched the gas engine, the B36:45, in September 2018. It is a separate engine rather than a variant of the B33:45, though the two share the block, the running gear, and most of the parts pool. The gas version fits different liners, pistons, and heads that open the bore to 360 mm while keeping the 450 mm stroke, and it holds 600 kW per cylinder at 750 rpm, the same output as the diesel. It ships in 6, 8, and 9-cylinder inline builds, and the vee range is now in the marine catalogue too: the B36:45V12P at 7,200 kW and the V16P at 9,600 kW, both at 750 rpm and 21 bar BMEP, with the V20 in the land gas range. This is the successor logic Bergen had already used on the B32:40, whose gas counterpart is the B35:40.

Bergen does not build a dual-fuel engine. It offers fuel flexibility instead, through the B3X platform marketed as B3X:45: an operator can convert an installed B33:45 diesel to the B36:45 gas engine, and back, by changing the fuel-specific parts while keeping the core. 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 when the bunker economics or the regulatory exposure shift, rather than being scrapped for a full replacement.

The B36:45 runs a 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 near top dead center. The lean charge keeps combustion temperature and the thermal NOx that forms with it low enough to meet IMO Tier III and EPA Tier 3 without after-treatment, cutting NOx by more than 90 percent against an equivalent diesel. Because natural gas is close to sulfur-free, sulfur-oxide and particulate emissions are close to eliminated, and Rolls-Royce cited up to 22 percent lower greenhouse-gas output than a diesel of the same power. Running on LNG as marine fuel , the B36:45 is a native Tier III solution rather than an add-on after-treatment fit.

The lean-burn Otto cycle carries one 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 gas, and Bergen states that its LNG-engine experience went into minimizing it through the gas-admission timing, the combustion-chamber geometry, and the piston-ring pack. The trade-off is general to the low-pressure gas medium-speed segment and is shared by the Wartsila 50DF and the equivalent MAN gas engines. The diesel B33:45’s acceptance of biofuels gives the platform a second decarbonization path that needs no gas conversion at all.

The gas engine reaches its largest form on land. The B36:45V generating set produces up to 12 MW of mechanical power at 600 kW per cylinder, against about 5 MW for the inline liquid-fuel B33:45L, which puts the gas vee at the top of the whole Bergen range. Stationary plants run the vee engines as base-load or peaking units, where the lean-burn Tier III combustion avoids the SCR train that a diesel plant of the same output would carry. On the marine side the vee sees less use than the inline engines, because a ferry or an offshore vessel usually needs the 3,600 to 5,400 kW band that the L6 to L9 already covers, and reaches for the V12 only when a single large prime mover suits the layout better than two inline engines.

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 worldwide without after-treatment, and reaches Tier III inside designated emission control areas with selective catalytic reduction fitted. The gas B36:45 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 development, with an SCR system included in 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 in-cylinder NOx formation below the limit. Closing the further gap to Tier III needs either the SCR after-treatment on the diesel or the switch to the lean-burn gas engine.

Selective catalytic reduction injects a 32.5 percent aqueous urea solution into the exhaust upstream of a vanadium-tungsten-titanium catalyst bed, where the urea breaks down to ammonia and the ammonia reacts with the NOx to give nitrogen and water vapor. Urea use 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 pick 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.

Applications

The B33:45 is concentrated in the vessel types where the Bergen line has been strong for decades, plus 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 one platform covers main propulsion, diesel-electric power, and stationary generation. About 40 units were contracted in the years right after the 2014 launch.

In the offshore-supply sector, the B33:45 powers anchor-handler tug-supply vessels, platform-supply vessels, subsea-construction ships, pipe-layers, 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 Rolls-Royce built into the engine matter for the dynamic-positioning duty, where the gensets have to absorb step changes in thruster demand without tripping.

In the fishing fleet, the B33:45 sits at the upper end of the world’s largest tuna seiners, longliners, and trawlers, a market the Bergen line has long 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.

The diesel-electric arrangement is what ties these offshore and drilling references together. Rather than couple the engine to a shaft, the plant runs several B33:45 gensets onto a common busbar and drives the propulsion thrusters through electric motors, so the engines can be loaded and shed in steps to match a demand that swings with the operation. That layout puts a premium on fast load acceptance and on the ability to run economically at part load, both of which Rolls-Royce built into the engine, and it lets a designer size the plant in whole-engine increments of 3,600 to 5,400 kW. The same generating-set engine then covers the hotel and process load at anchor.

In passenger shipping, the B33:45 drives RoPax and ferry propulsion, often in Norwegian and Mediterranean coastal service, 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 plants, where the V16 and V20 land engines carry the range into the tens of megawatts at the 540 kW-per-cylinder continuous rating. 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 plant loaded and shed to track the drilling 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.” Across a six-engine FPSO plant, the difference between a 600 kW and a 500 kW per-cylinder engine is several cylinders of maintenance scope over the fleet life.

Maintenance and operating characteristics

Bergen designs the B33:45 for up to 25,000 hours between major maintenance when the engine runs inside 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 held inside its design load window reaches the longer interval, while one cycled hard or run at sustained low load reaches a service earlier. Equipment health monitoring feeds the scheduling and can align the overhaul with the vessel’s re-classification survey, which moves the 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 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 stays open. The pool-exchange model, where overhauled heads and injection components come from a shared pool and the removed parts go ashore for reconditioning, keeps port-call downtime short and moves the bench work off the vessel. For an engineering officer, the load-bearing 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 signals the health-monitoring system reads.

Bergen Engines supports the B33:45 through service centers in Norway, the UK, the US, Brazil, and Singapore, with authorized agents in additional ports and 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 base remains a real strength for fleets that work from Northern Europe. Officers joining a B33:45-powered vessel for the first time work to the same medium-speed watchkeeping discipline set out in the marine diesel engine reference.

Comparison with competing medium-speed engines

The B33:45 competes mainly 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 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 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 service network is often the deciding factor. Wartsila claims lifecycle coverage in more than 70 countries, and MAN runs its PrimeServ network on a similar global scale, both larger than Bergen’s footprint of centers in Norway, the UK, the US, Brazil, and Singapore. For a Northern European owner running out of Norwegian and North Sea ports, the Bergen network is close and the response time short; for a global tramping operator, the wider Wartsila or MAN presence can weigh more. The fuel strategy pulls the other way for some owners. The B33:45 and B36:45 pairing lets a fleet start on diesel and convert to gas later through the B3X platform, where the Wartsila 32 reaches the same Tier III gas capability through the separate W32DF dual-fuel engine rather than a like-for-like core swap. HiMSEN’s H35 competes in the same bore class in Asian genset and offshore markets on price and on HD Hyundai’s integration with its own two-stroke main engines.

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. At 720 rpm the same stroke gives 10.8 m/s. 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, so 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 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 sets the project rating subject to the application. The SFOC figures of 177 g/kWh at full load and 175 g/kWh at 85 percent MCR are best-point values on MDO at 42.7 MJ per kg and do not represent the in-service average across a real operating profile. The L6 dry weight of 40,210 kg excludes the flywheel and the transport foundation, so an installed engine weighs more.

The gas-engine 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 B36:45 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 against the live Bergen data sheet, since the company states its data may change with continuous development. The competitor figures in the comparison table are approximate and are meant 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.

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