In 2025, most data sources report that machinery failure was the major cause of all shipping casualties. In 20 years as an engineer surveyor in international marine consultancies, machinery failures have constituted around 60% of my work, with 45-50% involving the heart of most commercial ships, the marine Diesel engine. Without it the ship cannot function, and when it malfunctions, the consequences can be catastrophic.
Types of Diesel engine failures encountered
The Diesel engine has changed significantly from the difficult transition to heavy fuels in the 1970s, to the recent return to lighter fuels, which should in theory be engine friendly. Yet breakdowns continue, most commonly from component failure and fuel quality issues.
The crankshaft failure
The costliest Diesel engine component failure remains the crankshaft which can immediately incapacitate a ship’s propulsion and cause loss of electrical power. The crankshaft, particularly the crankpin and crankpin bearing, is generally the most highly loaded part of Diesel engines, because it is subject to rotating cyclic load that makes efficient lubrication challenging. Any neglect, such as inattention to lubricating oil quality, improper tightening of bolts, fitting of poor-quality parts, or running outside the manufacturer’s recommendations, and the engine will fail, usually very quickly and disastrously in the case of high-speed Diesels.
On large slow-speed two-stroke engines fault detection is easier and a temporary repair is often possible by removing a connecting rod and running the engine with the cylinder unit isolated, but that relies on the skill and motivation of the crew.
Failures due to poor fuel quality
A second, common, costly failure of the Diesel engine stems from poor-quality fuel, either from deleterious contaminants supplied in the bunkers at delivery or inadequate onboard cleaning and conditioning before the fuel reaches the engine.
Poor quality fuel is indiscriminate in its effects and will often incapacitate all Diesels, main engine and generators alike. Fuel pumps, fuel injectors, and cylinder liners can be affected, bringing the ship to a stop. If the problems become severe, the crew becomes overloaded, motivation and ability to repair the damage drops, spare parts run out, and tugs are called.
Typical costs and consequences
Cost
There are many other ways an engine can fail as man’s inhumanity to machines knows no limits and engineering is not an exact science. While engine manufacturers’ R&D has taken the Diesel engine close to the limits of what current technology and materials allow, it leaves few tweaks to improve reliability, these two remain the common and expensive failures.
A large two stroke engine crankshaft failure can cost as low as $200,000 if only minor machining is necessary, or as much as $10-15M if the crankshaft needs replacing. The latter is rare, as these engines are well monitored with protection devices that give warnings before serious damage is done. Ironically, the biggest damage I have seen came when crews ignored those warnings, choosing to diagnose a faulty sensor rather than admit to lubricating oil failure or water contamination.
Medium and high-speed engines are a different story. A failed crankpin bearing on a medium speed engine often means replacing the crankshaft, typically $200,000-$500,000, while complete engine replacement is often more economical than repair for high-speed engines.
Serious fuel contamination causing multiple main and generator engine failures can cost US$500,000 for fuel pump and injector damage and can rise above $1M if cylinder liners and expensive electronic injection components are affected and tugs are called.
Consequences
The biggest consequence is harm to the crew. Having stood next to an engine in the final throes of failure, I recommend the safest place is on the bridge with the navigators well away from ejected hot and heavy fragmented engine parts, hot oil, and a potential flame front.
Secondary consequences may include fire, loss of electrical power, loss of propulsion, collision, grounding, loss of hire, and loss of reputation.
What follows will be long hours of repair work, if it’s possible, with limited assistance and the vessel at the mercy of the sea. Even with the ability and training to perform the work, motivation soon abandons the best of them and the expensive assistance call goes out.
New technology, new problems
The modern Diesel engine has become harder for the seafaring marine engineer to deal with when things go wrong. While the basic technology of Diesel engines’ moving parts remains largely the same, 40 years of demands for fuel efficiency, space efficiency, emissions reduction, and new fuels have produced an engine that is more sensitive to poor maintenance, errors and more demanding to repair.
There is also an ever-increasing reliance on a smaller choice of engine manufacturers for maintenance and repair, and marine engineers are becoming operators rather than all round engine caretakers. This erodes the crew’s ability to get a stricken vessel safely to the next port under its own power.
Waiting time for non-routine damaged parts is also growing. As they are no longer kept on the shelf, owners must factor this into the emergency planning: do we build redundancy, standardise equipment, or keep a spare crankshaft, camshaft, or software, all of which can take up to a year to arrive?
Add highly volatile new fuels which require careful handling during maintenance and repair cycles, and it is hard to conclude that the risk profile of ships is any better now than it ever was.
Loss prevention advice
So, what can be done to lower the risk profile of a modern vessel?
Back to basics on crankshafts
- Follow manufacturers advice: work with them when issues arise, consult when planning fuel changes, review service letters and have them attend for regular health checks.
- Perform regular crankcase inspections, with specific attention to connecting rod bolt tightness.
- Ensure hydraulic jacks and tools are working and properly calibrated.
- Replace bottom-end nuts and studs as manufacturers recommend.
- Monitor crankpin and connecting rod dimensions (ovality).
- Carry out regular testing and trending on:
- Oil analysis
- Cylinder liner oil scrape down
- Walk the engine room to detect unusual noise, vibration, smell, or heat by touch, as the camera in the control room cannot detect these.
Back to basics on fuel
- Check fuel purifier performance regularly.
- Use fuel filters with correct mesh size as recommended by manufacturers.
- Always keep an alternative source of fuel available on board.
- Don’t use a fuel until it has been tested.
Crew competence and motivation
Poor competence and motivation are primary factors in machinery failures. The marine world is largely out of sight and out of mind until a canal is blocked or a bridge is hit — and most of the ships I attend for technical failures are manned by beleaguered crews, low in morale. But there are basics that can be done:
- Apply good due diligence when building a competent team.
- Visit the ships regularly and assess morale.
- Give the crew your time and train them where possible.
- Provide good basic technical reference material on board.
- Equip the crew properly with PPE.
- Bring crew through the manager’s office for regular interviews.
- Deal with small issues and reported defects quickly, before they become bigger.
- Watch for unapproved modifications.
Mr Graeme Temple is the Global Specialty – Managing Director Marine Technical Services, APAC at Sedgwick.