Search for “tanker engine” and one of the first results is a photo of a 14-cylinder diesel that weighs over 2,300 tonnes and makes more than 100,000 hp. It’s a magnificent machine. It’s also not a tanker engine. It was designed for large container ships, and the first 14-cylinder unit went into a container ship in 2006 (Wärtsilä RT-flex96C).

The engine in a real VLCC is smaller, slower and more interesting if you’re the one who has to keep it running. At the same time, it’s being asked to do more: burn less fuel, meet stricter emission rules, and stay within the power limits many tankers now run with.

This guide covers which engines tankers use at each size, why they’re built the way they are, what else runs in a tanker engine room, and which parts wear out. It skips most of the history.

What engine does an oil tanker use?

The main engine on a tanker is a two-stroke crosshead diesel. It’s large, slow and long-stroke, and it’s bolted directly to the propeller shaft. There’s no gearbox and no clutch: when the engine turns at 75 rpm, so does the propeller.

Two design families dominate the market:

• Everllence B&W (formerly MAN B&W): the G, S and ME-C engines, plus dual-fuel versions. Everllence covers tankers from small coastal vessels up to ULCCs (Everllence).
• WinGD: the X engines, the successor to the Wärtsilä and Sulzer two-stroke line.

Most of these engines aren’t built by Everllence or WinGD. They’re designed there and built under licence by engine works in Korea, China and Japan, usually close to the shipyard. That detail matters later, when you order parts.

Why two-stroke and not four-stroke?

Big question, but the short answer is propeller efficiency. A large propeller turning slowly moves a lot of water efficiently. A two-stroke engine can run at the propeller’s own speed, so it can drive it directly.

The numbers make the point. In an Everllence study of a 47,000 dwt MR tanker at 15.1 knots, moving from a 5.9 m propeller at 127 rpm to a 6.7 m propeller at 100 rpm cut the required engine power from 9,960 kW to 9,310 kW (MAN Energy Solutions, 2019). Same ship, same speed, 650 kW less. That’s why modern “ultra-long-stroke” engines exist: a longer stroke lets the engine turn more slowly and swing a bigger propeller.

Four-stroke diesel engines do appear on tankers, but mostly as auxiliary engines for power generation, on small coastal tankers, and in the electric propulsion of some gas carriers.

How to read a tanker engine’s name

A designation like 7G80ME-C9.5 is a bit of a mouthful. It’s also the most useful line on the nameplate.

WinGD uses a similar logic: an X72DF has a 72 cm bore and runs on dual fuel.

Tanker engine size by tanker class

The tanker class sets the engine size. Here are real examples, from product tankers to the largest crude carriers.

Deadweight ranges follow the commonly used AFRA and flexible market scales. Power figures are for the named ships or engines. Your ship’s figure depends on its design, derating and any power limit.

SMCR stands for “specified maximum continuous rating”, which is a fancy way of saying the power the engine was set up to deliver on this particular ship. The same engine model can be rated quite differently on two ships.

So how big is an oil tanker engine?

In horsepower, a VLCC engine of around 22,500 kW is roughly 30,000 hp. The largest tanker engines, like the ULCC example above, pass 50,000 hp. Physically, a two-stroke main engine rises through several decks, and the engine room is designed around it.

The largest ship ever built, the 564,763 dwt Seawise Giant (1979–2009), didn’t have a diesel at all. It used two boilers and a steam turbine rated at 50,000 hp (Wikipedia). Steam lost to diesel on fuel consumption. If your fleet includes older tonnage, though, you’ll still meet the generation in between: Sulzer RTA and MAN B&W MC engines, which are still running and still need parts.

What else runs in a tanker engine room?

The main engine gets the attention, but it’s only one of several engines on board. Here’s the rest of a typical tanker engine room.

Auxiliary engines (gensets). Medium-speed four-stroke engines make the ship’s electricity, and most tankers carry three or more sets. The usual names are Hyundai HiMSEN, Daihatsu, Yanmar and Everllence or Wärtsilä four-strokes. The designation logic is similar: a HiMSEN 6H21/32 has six cylinders, a 21 cm bore and a 32 cm stroke.

Boilers and cargo pumps. This is where tankers differ from bulk carriers.

• Crude carriers usually discharge with large cargo pumps in a pump room, driven by steam turbines. The ship’s boilers supply the steam, and also heat the cargo and fuel.
• Product and chemical tankers usually have a deepwell pump in each cargo tank. These are driven electrically or hydraulically, with no pump room (Marine Insight).

Everything else: the inert gas plant, fuel and lube oil purifiers, fresh water generator, compressors and an emergency generator.

What slow steaming and EEXI mean for the engine

Since 2023, existing ships have had to meet IMO’s EEXI efficiency requirement. Many tankers comply with an engine power limitation (EPL) or shaft power limitation (ShaPoLi). EPL limits the maximum amount of fuel injected per stroke, and it has to be documented in an approved onboard manual (DNV, 2025).

Here’s what that means in practice: engines spend more hours at low load. Low-load running tends to foul turbochargers and exhaust gas boilers faster, and it changes how the cylinders wear. The makers publish low-load guidance. Follow it, and watch the parts it names.

Fuel is the other reason speed stays low. Published estimates put a VLCC at roughly 60–100 tonnes of fuel a day, a Suezmax at 45–60 and an MR tanker at 25–40 (Maritime Page, 2026). Let’s be careful with these, though. They depend on speed, weather, hull condition and whether the ship is laden or in ballast. Here’s what they mean in practice: for a VLCC, saving five tonnes a day over 300 days at sea is 1,500 tonnes of fuel a year.

Dual-fuel tanker engines

New fuels are arriving in the tanker fleet too. In 2021, ten 300,000 dwt VLCCs were ordered with 7G80ME-GI engines that burn LNG or fuel oil, for charter to Shell (MarineLink). WinGD’s X-DF engines went into LNG-fuelled Aframaxes from 2018, and methanol-capable engines followed for Suezmaxes and VLCCs.

For purchasing, this matters because a dual-fuel engine adds a whole gas or methanol system, with its own valves, seals and sensors. Those are new part numbers, with shorter supply histories.

What wears out on a tanker main engine?

A two-stroke main engine is built for very long service, but the same parts keep coming back on the repair list. The figures below come from Everllence (then MAN) service experience published in 2008 (Riviera). They show the scale involved. They aren’t your ship’s intervals.

That’s the theory. At sea, fuel quality, cylinder oil feed rate, hours at low load and the last overhaul all change the picture. Your intervals come from the maker’s current instruction manual and service letters, plus the measurements your engineers take at each overhaul.

Imagine the scene. A VLCC is due to load in four days. At the last scavenge port inspection, the second engineer found broken rings on unit 4. The spare ring set is on the inventory list but not on the shelf, and the quote in the inbox says three weeks. So who decides: the chief engineer, the superintendent or the purchaser? In practice, whoever is under the most time pressure. Every option that follows costs more than the ring set would have cost sitting in the store.

Which tanker engine spares to keep, and how to order them

Start with the maker’s recommended spares list and the class requirements. On top of that, well-run tanker engine rooms usually keep:

• A complete exhaust valve, or at least a spindle and seat. Lead times can be long, and a leaking valve affects the whole unit.
• Fuel valve nozzles and overhaul kits. They’re used constantly.
• Piston rings and a full set of gaskets and O-rings for a unit overhaul. A unit opened without them stays open.
• Bearing shells for the most critical positions, where lead times justify it.
• Genset spares: fuel injection pumps and valves, plus cylinder head gaskets for the auxiliary engines.
• Turbocharger spares, as covered in our turbocharger guide.

To get the right part the first time, send:

1. Engine designation and mark (for example 7G80ME-C9.5), plus the engine builder and serial number. A photo of the nameplate is ideal.
2. Part numbers and plate or item numbers from the maker’s spare parts catalogue.
3. Main engine or genset, and for a genset, its own maker, model and serial number.
4. The documentation you need for class, PSC or company records.
5. Port and ETA.

The engine builder matters because the same design is built by different licensees. The mark matters because it can change the part even when the name stays the same. Ordering from a photo of the old part alone is… optimistic. Here’s why the wrong part number can cost you more than the part itself.

The main message

A tanker engine isn’t one engine. It’s a slow two-stroke main engine plus its turbocharger, gensets, boilers and cargo pumps, and each has its own makers, marks and part numbers. Know the designation, keep the slow-to-get parts on board, and order against the serial number, not the photo.

Need spares for Everllence/MAN B&W, WinGD/Wärtsilä or Sulzer tanker engines, or for the gensets beside them? Send the part number and a nameplate photo. We’ll confirm today. Engine spare parts → · Send a request →

Fuel is expensive, schedules are tight, and every engine at sea is being asked to do more with less. The marine turbocharger sits right in the middle of that pressure. When it works, nobody mentions it. When it doesn’t, exhaust temperatures climb and someone in the office starts looking up OEM lead times.

This guide covers how a marine turbocharger works, which parts wear out, and which spares to keep on board so that a turbo problem doesn’t become an off-hire problem.

Quick answer: a turbocharger uses the engine’s own exhaust gas to spin a turbine. The turbine drives a compressor on the same shaft, which pushes more air into the cylinders. More air means more complete combustion, so the engine makes more power without getting bigger.

What does a turbocharger do on a ship?

A diesel engine can only burn as much fuel as it has air for. The turbocharger supplies that air, far more than the engine could draw in on its own.

It does this almost for free. The energy comes from exhaust gas that would otherwise go straight up the funnel, so you are recovering heat you have already paid for. You’ll find turbochargers on the main engine and on the auxiliary engines of almost every commercial ship.

How does a marine turbocharger work? Step by step

It’s not rocket science, but it is fast.

1. Exhaust gas drives the turbine

Hot exhaust gas leaves the cylinders and passes through the nozzle ring, a ring of guide vanes that directs the gas onto the turbine blades. The turbine spins at very high speed: tens of thousands of rpm on smaller units.

2. The shaft turns the compressor

The turbine and the compressor wheel sit on one shaft, supported by bearings. Whatever the turbine does, the compressor does too.

3. The compressor pressurises the air

The compressor draws in engine room air through a filter and silencer and compresses it. Compression also heats the air.

4. The charge air cooler cools it down

Hot air is less dense. The charge air cooler, the marine equivalent of an intercooler, cools the air so that more oxygen fits into each cylinder.

5. Dense air enters the cylinders

On a two-stroke engine, the air goes into the scavenge air receiver. On a four-stroke, it goes into the intake manifold. The exhaust from that combustion then drives the turbine again. At low load there isn’t enough exhaust energy, which is why large two-stroke engines have auxiliary blowers that cut in to help.

Axial, radial, and why “matching” matters

Large turbochargers on two-stroke main engines usually have an axial-flow turbine. Smaller units on four-stroke engines and gensets usually have a radial-flow turbine. The principle is the same; the spare parts are not.

Then there’s turbocharger matching, which is a fancy way of saying the turbocharger is set up for one specific engine. Parts like the nozzle ring are selected to suit the engine’s rating, so two turbochargers of the same model can need different nozzle rings. That’s why the serial number matters more than the model name when you order.

What wears out on a marine turbocharger

A turbocharger runs hot, fast and continuously, and the same parts keep ending up on the repair list.

Surging: the sound nobody likes

Surging is when the compressor can’t push air against the pressure downstream and the airflow briefly reverses. You’ll hear it as a bark or a bang. Anyone who has stood in an engine room during surging doesn’t need it described twice.

The usual causes are a fouled nozzle ring or turbine, a dirty air filter, a fouled charge air cooler or sudden load changes. Repeated surging loads the bearings and blades, so treat it as a symptom. Regular washing, as the maker specifies, is the cheapest prevention: fouling left alone becomes imbalance, and imbalance becomes bearing damage.

Which turbocharger spares to keep on board

The honest answer is that it depends on the model, the engine and how far the vessel trades from a reliable supplier. Start with the maker’s recommended on-board spares list. Beyond that, this is what well-run engine rooms tend to carry:

Picture the scene. The vessel sails in 36 hours. The chief engineer reports rising exhaust temperatures and a bearing that doesn’t sound right on run-down. The spare bearing set is on the list but not on the shelf, and the OEM quotes four weeks. So who decides: sail at reduced load, delay, or fly the part in? Whichever option wins costs more than the bearing set would have cost sitting in the store.

OEM or OEM-spec?

For bearings, nozzle rings and rotating parts, stick to genuine or verified OEM-spec parts. They spin at very high speed next to very hot gas, and small tolerance errors don’t stay small. For mats, gaskets and O-rings, a verified quality equivalent is fine. More on this in OEM vs Aftermarket Marine Parts: What’s Actually the Difference?

How to order turbocharger spares without guesswork

Ordering from a photo of the old part alone is… optimistic. Send this instead:

1. Turbocharger maker, model and serial number (a nameplate photo is perfect)
2. Engine maker and model, and whether it’s a main or auxiliary engine
3. Part numbers from the maker’s manual
4. The documentation you need for class or company records
5. Port and ETA

Getting this right matters more than it looks. Here’s why the wrong part number can cost you more than the part itself. For maintenance intervals, follow the maker’s guidance, for example Accelleron or Everllence.

The main message

A turbocharger rarely fails without warning. Watch the exhaust temperatures, scavenge air pressure and bearings, keep it clean, and keep the slow-to-get parts on board. The cheapest turbo spare is the one already on the shelf.

Need spares for ABB/Accelleron, MAN or MHI turbochargers? Send the part number and a nameplate photo. We’ll confirm today.

Turbocharger spare parts → · Send a request →

FAQ

What does a turbocharger do on a ship’s engine?

It uses exhaust gas energy to drive a compressor that forces more air into the cylinders. That allows more complete combustion, so the engine makes more power and uses fuel more efficiently.

What does “turbocharger” mean?

It combines turbine and supercharger. A supercharger forces extra air into an engine; a turbocharger does the same using a turbine driven by exhaust gas.

What causes turbocharger surging?

A brief reversal of airflow through the compressor, usually caused by a fouled nozzle ring or turbine, a dirty air filter, a fouled charge air cooler or sudden load changes.

Can a ship run if the turbocharger fails?

Often yes, at reduced load. Many engines let you lock or blank off a failed turbocharger. Check the maker’s instructions and make sure the emergency kit is on board.

Which turbocharger spares should always be on board?

A complete bearing set, a gasket and sealing ring set, filter mats, cleaning materials and the emergency locking or blanking kit. Add a nozzle ring if the vessel trades far from reliable supply.

Not all engine failures are surprises. A lot of them are predictable. The same parts, across the same engine types, fail for the same reasons — wear, heat, pressure, and time. If you have been working in engine rooms long enough, you already know which jobs come up again and again. This is a straightforward look at the parts that keep ending up on the repair list, and why.

Fuel injectors and injection nozzles

Injectors take continuous punishment. They operate under high pressure, at high temperature, thousands of times per hour. Over time, nozzles wear, spray patterns change, and combustion becomes uneven. You start seeing higher exhaust temperatures on individual cylinders, black smoke that does not clear, and a gradual drop in performance.

The problem is that degraded injectors do not always fail cleanly. They fade. By the time the symptoms are obvious, there is often secondary wear on the cylinder liner and piston rings from the uneven combustion. Keeping a set of tested spare nozzles onboard means you can swap and test rather than wait for a supply chain to catch up with you.

Piston rings and cylinder liners

These are the parts that take the direct force of combustion. Rings wear against the liner, the liner wears against the rings, and over time the seal between them degrades. You get blow-by, oil consumption increases, and eventually compression drops enough to affect starting and power.

Liner and ring wear is gradual, which makes it easy to underestimate. Running worn rings for too long accelerates liner wear to the point where the liner needs replacement — a significantly bigger job than a ring change. Keeping a spare set of rings for your main engine is one of the most straightforward insurance policies in the engine room.

Water pump impellers

The raw water impeller is one of the most commonly replaced parts on any marine diesel. It is made from rubber, it runs against a metal housing, and it degrades with time — faster if the engine is run dry even briefly, faster again in warm or debris-heavy water.

When an impeller fails, blades break off and travel through the cooling system. They end up in the heat exchanger, in the thermostat housing, blocking flow at exactly the point where you need it most. The impeller itself is cheap. Finding and clearing every broken blade from the cooling circuit is not.

Change impellers on a schedule, not when they fail. And keep at least one spare — preferably two — matched to your engine.

Fuel and oil filters

Filters are the most basic item on this list, and the most often overlooked. Clogged fuel filters starve the injection system. Clogged oil filters can trigger a bypass valve that sends unfiltered oil through the engine. Neither of these is a good situation.

The failure mode here is not the filter itself — it is running filters past their service life because the next supply delivery is three weeks away. Carrying a full set of spares for every service interval means this never becomes a decision you have to make under pressure.

Thermostats

A stuck-open thermostat means the engine never reaches operating temperature. It runs cool, fuel combustion is incomplete, and liner wear accelerates. A stuck-closed thermostat is more immediately dangerous — the engine overheats quickly. Either way, the thermostat is a small part with a significant effect on everything downstream of it.

Thermostats are inexpensive and take up almost no space. There is no good reason not to carry a spare. The number of overheating faults that turn out to be a failed thermostat makes this one of the best-value items you can have on a shelf.

Seals and gaskets

Head gaskets, exhaust manifold gaskets, heat exchanger seals — any of these failing means fluid going where it should not. Water in the oil, exhaust leaking into the engine room, coolant bypassing the cooling circuit. The gasket itself costs almost nothing. The damage that follows a failed gasket does not.

Keeping a full gasket set for your main engine is standard practice in well-run engine rooms. If you are sourcing from a supplier who does not ask for your engine serial number before supplying a gasket set, ask the question yourself — the wrong thickness or material specification will cause more problems than the failed gasket did.

Bearings

Main and auxiliary engine bearings wear over time, especially if oil quality or filtration has not been maintained consistently. Bearing wear shows up in oil analysis before it shows up as noise — which is why regular oil sampling matters. When bearings do need replacing, having the correct shells onboard avoids the wait for a critical part to arrive at whatever port you happen to be at.

The point

None of these parts are exotic. They are not expensive relative to what happens when they are not available. The engine room where these items are stocked and rotated on a schedule runs with far less unplanned downtime than the one ordering parts reactively after a failure.

Know your engine. Know its service intervals. Stock accordingly.

Walk into any conversation about marine spare parts and this question comes up quickly. Should you buy OEM — original equipment manufacturer — or is aftermarket good enough? The answer is not as simple as either side of the debate usually makes it sound.

Here is an honest breakdown of what the difference actually is, where it matters, and where it does not.

What OEM actually means

OEM stands for Original Equipment Manufacturer. An OEM part is sourced through the engine manufacturer — it carries their part number, their documentation, and their guarantee that it meets the exact specification the engine was built to.

What most people do not know is that engine manufacturers rarely make all their own parts. A major marine diesel maker might produce its own crankshafts and cylinder heads, but outsource the manufacture of fuel injection components, turbocharger parts, or seals to specialist third-party manufacturers. Those third-party factories produce parts to the engine maker’s specification, package them in OEM boxes, and ship them through the authorized supply chain.

So when you buy an OEM part, you are buying the specification, the traceability, and the warranty — not necessarily a part made in-house by the engine manufacturer.

What aftermarket actually means

Aftermarket parts are made by third-party manufacturers and sold outside the engine maker’s official supply chain. The quality range here is enormous.

At the top end, you have established aftermarket manufacturers who produce parts to the same — or sometimes better — specification as the OEM equivalent. Some of these factories are literally the same factories that supply the engine makers, producing identical parts without the OEM label.

At the bottom end, you have parts with no credible quality control, made from inferior materials, with tolerances that may look correct on the outside but fail under operating conditions. These are the parts that cause problems — not because they are aftermarket, but because they are poor quality.

The word “aftermarket” covers everything from reputable industrial manufacturers to parts with no traceable origin. That is the part of this conversation that often gets missed.

Where OEM matters most

For critical internal components — fuel injection equipment, turbocharger assemblies, cylinder liners, piston rings, and bearings — the case for OEM or high-quality equivalent is strong. These parts operate under extreme conditions, and tolerance deviations that are invisible on a shelf can cause real damage inside a running engine.

OEM parts also come with full documentation. For class surveys and PSC inspections, being able to show that the correct approved parts were installed matters. A part with no traceable documentation is a liability during an inspection, regardless of whether it is performing correctly.

There is also the warranty and insurance dimension. Many engine manufacturer warranties require OEM parts for warranty claims to be valid. Some P&I clubs and hull insurers take an interest in part specification when investigating damage claims. Using non-OEM parts in critical systems without the approval of the engine maker can complicate those conversations.

Where aftermarket holds up

For consumables and high-turnover items — filters, seals, anodes, impellers, gaskets — a quality aftermarket part from a reputable manufacturer is a perfectly sound choice. These parts are simple by design, and the performance gap between a well-made aftermarket item and the OEM equivalent is small to none.

The key word is reputable. Buying filters or impellers from a supplier who cannot tell you who made them or what specification they were built to is a different matter. A failed impeller sends broken blades through your cooling system. A filter that bypasses under pressure does nothing. The cost of the part is small — the cost of what follows is not.

The practical answer

The question should not be OEM or aftermarket as a blanket policy. It should be: what is this part doing, what happens if it fails, and do I have confidence in what I am buying?

For critical engine components under load, use OEM or an aftermarket equivalent from a manufacturer you can verify. For consumables and routine service items, a quality aftermarket option works well — and can make sense from a cost and availability standpoint, especially in ports where OEM supply chains are slow.

What to avoid in every case is buying on price alone, from a supplier who cannot confirm specification, make, or traceability. That is where the real risk sits — not in the OEM versus aftermarket label.

Every engineer has been there. A part arrives, you open the box, and something is slightly off. Maybe the thread pitch is wrong. Maybe it looks identical but sits a millimetre too short. Maybe it fits — but only just. You install it anyway because the vessel is sailing in six hours.