What Breaks Most on Ships? The Dirty Dozen of Maritime Failures
June 12, 2025
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Across thousands of maintenance reports, surveys, and real-world incidents, a clear pattern emerges: a small group of ship components cause the majority of breakdowns, delays, and costly repairs.
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This list cuts through the noise and gets straight to the parts that most often leave ships dead in the water. From failed turbochargers to cooling pump collapses, these are the 12 components you need to monitor closely if you want to avoid unplanned downtime and six-figure repair bills.
1️⃣ Engine Cooling Pumps (expand)
Engine cooling pumps circulate seawater or freshwater through the engine’s cooling system to prevent overheating. They’re essential for maintaining safe engine temperatures during operation.
⚠️ Why It Fails:
- Impeller wear and seal degradation from constant use.
- Blockages due to debris or scale buildup in piping.
- Overheating or electrical failure of the motor (in electric-driven types).
- Typical replacement cost: $5,000 – $15,000 depending on pump size and system.
- Emergency repairs in port can add delay penalties and dock fees.
- Inspect and lubricate pump bearings every 1,000 hours of operation.
- Flush cooling system periodically to remove scale and sediment.
- Check and replace seals annually to avoid coolant leakage.
- Keep spares on board — especially impellers and seals.
- Use vibration analysis and flow sensors to detect early pump performance decline before full failure occurs.
Bottom line: Cooling pumps are high-usage, high-risk components. Regular checks and onboard spares can be the difference between a smooth crossing and a costly diversion.
2️⃣ Propulsion Shaft Bearings & Shaft-Line (expand)
The propulsion shaft-line transmits torque from the main engine to the propeller. Bearings along the shaft (especially the stern tube bearing) support and align it, ensuring efficient propulsion and minimizing vibration.
⚠️ Why It Fails:
- Wear over time due to misalignment, shaft deflection, or vibration.
- Oil contamination or leakage in the stern tube can cause metal-on-metal contact.
- Overloading the propeller or poor shaft alignment during dry dock work.
- Typical bearing replacement: $15,000 – $50,000.
- Full shaft-line realignment or stern tube work can exceed $100,000.
- Unplanned failures can take a vessel out of service for weeks.
- Conduct regular shaft alignment checks, especially after dry dock periods.
- Monitor stern tube oil quality and pressure — contamination is an early failure sign.
- Use vibration and acoustic monitoring systems to detect bearing wear or shaft imbalance.
- Lubrication system maintenance is critical — inspect and flush during every scheduled overhaul.
- Check for signs of “whirling” or excessive axial movement — this may point to early shaft misalignment or bearing degradation.
Bottom line: The shaft-line is the heart of propulsion. Ignoring minor bearing wear or oil issues can lead to major, expensive failures that put a ship out of commission for weeks.
3️⃣ Busbars / Circuit Breakers (expand)
Busbars and circuit breakers form the backbone of a vessel’s electrical distribution system. They route and control power from generators to vital systems including navigation, propulsion auxiliaries, and safety gear.
⚠️ Why It Fails:
- Overheating from poor ventilation or insulation breakdown.
- Corrosion due to humidity or saltwater ingress in panel rooms.
- Poor maintenance or mechanical wear from repeated cycling.
- Faulty installation or overloaded systems can trigger arcs or trips.
- Individual breaker: $5,000 – $15,000.
- Busbar repair or replacement: $10,000 – $50,000 or more depending on the complexity.
- A full blackout incident may cause port delays, safety risks, or collision liability.
- Perform thermal imaging scans during operation to detect hotspots.
- Inspect insulation resistance regularly, especially in high-humidity environments.
- Keep electrical rooms dry and clean, and replace gaskets or door seals as needed.
- Check tightness of connections and breaker functionality during each dry dock.
- Label and track the cycling history of each breaker. High-cycle breakers are more likely to fail under stress and should be prioritized for replacement or upgrades.
Bottom line: Electrical failures like busbar faults and tripped breakers are quiet threats. They rarely give warnings — but when they hit, the consequences can be sudden, dangerous, and expensive.
4️⃣ Auxiliary Engine Cooling Controllers / Valves (expand)
These valves and control units manage the flow of cooling water through auxiliary engines, ensuring they stay within safe operating temperatures during electrical power generation and standby operation.
⚠️ Why It Fails:
- Valve scaling or blockage from sediment and mineral buildup.
- Sensor failure or wiring faults in automatic control units.
- Improper calibration or mechanical wear causing poor flow regulation.
- Unnoticed cooling issues may lead to complete generator shutdown.
- Valve or controller replacement: $5,000 – $20,000.
- Damage to auxiliary engine from overheating can exceed $50,000 in major cases.
- Unexpected generator failure increases fuel consumption and redundancy risk.
- Flush cooling lines regularly to prevent scaling or algae buildup.
- Test control units monthly using manual override to ensure proper actuation.
- Verify sensor inputs through diagnostic tools — especially in humid or hot environments.
- Clean or replace valve seats and actuators during each scheduled maintenance interval.
- Keep a pre-calibrated spare controller and key valve kit onboard. Swapping units in minutes during failure can prevent hours of lost power generation capacity.
Bottom line: Auxiliary engine cooling issues often start small — a sticky valve, a slow sensor. But left unchecked, they can cascade into full auxiliary system failure with steep costs and critical power loss risks.
5️⃣ Pump Mechanical Seals & Bearings (expand)
Found in systems ranging from bilge and ballast to cooling and firefighting, pumps rely on mechanical seals to prevent leakage and bearings to support the rotating shaft. These are among the most frequently replaced components aboard.
⚠️ Why It Fails:
- Wear from constant shaft rotation and vibration.
- Seal degradation due to temperature fluctuations and chemical exposure.
- Improper alignment or over-tightening during installation.
- Lack of lubrication or contaminated lubricants in bearing housings.
- Typical seal kit or bearing change: $2,000 – $8,000 per pump.
- Total pump rebuild: $10,000 – $25,000 depending on size and type.
- Failure during operations can lead to system downtime or safety violations.
- Inspect seals for signs of wear or leaks during routine checks.
- Use OEM-approved lubricants and change them at recommended intervals.
- Ensure pump alignment and coupling balance during reinstallation.
- Monitor vibration and temperature trends to detect early bearing failure.
- Don’t just replace a leaking seal — inspect the shaft surface for scoring. Minor imperfections can tear new seals and cause repeat failures.
Bottom line: Pump seals and bearings are wear-and-tear items that often fail quietly until there's a leak or noise. A small investment in monitoring and replacement planning can prevent major disruptions across multiple ship systems.
6️⃣ Turbocharger Bearings (expand)
Turbocharger bearings support the high-speed rotation of the turbine shaft, allowing the turbocharger to compress air into the engine and boost power output. These bearings operate under extreme temperatures and speeds, often exceeding 100,000 RPM.
⚠️ Why It Fails:
- Oil contamination or degradation causing loss of lubrication film.
- Thermal fatigue due to rapid load changes or shutdowns.
- Rotor imbalance or excessive shaft vibration leading to bearing wear.
- Poor maintenance or failure to observe proper cool-down procedures.
- Turbocharger bearing overhaul: $40,000 – $120,000.
- Full turbocharger replacement (if damaged): $150,000 – $300,000+
- Failure mid-voyage may result in reduced engine power or complete diversion.
- Monitor oil pressure and temperature at turbocharger inlet and outlet points.
- Use oil filtration systems and change filters frequently to avoid contamination.
- Follow manufacturer-specified cool-down procedures before shutdowns.
- Inspect rotor balance and bearing clearance during routine overhauls.
- Install a bypass oil filter system specifically for the turbocharger loop. This dramatically improves oil cleanliness and extends bearing life, especially in high-hour engines.
Bottom line: Turbocharger bearings may be small, but when they fail, they take power and profit with them. Precise oil management and operational discipline are the keys to keeping these high-speed components alive.
7️⃣ Fuel Injector System (expand)
Fuel injectors spray pressurized fuel into the engine’s combustion chamber with high precision, controlling the air-fuel mixture and combustion timing. Efficient injector function is critical for power output, fuel economy, and emissions control.
⚠️ Why It Fails:
- Contaminated or low-quality fuel causing internal clogging or scoring.
- Wear and tear on nozzles and seals from high-pressure cycling.
- Incorrect injection timing due to faulty actuators or control modules.
- Carbon buildup restricting spray pattern and reducing atomization.
- Single injector replacement: $3,000 – $10,000.
- Full bank of injectors on a large engine: $30,000 – $60,000+.
- Poor injection can cause misfires, excess fuel consumption, or engine overheating.
- Install high-quality fuel filtration systems and replace filters routinely.
- Conduct periodic injector spray pattern tests and nozzle cleaning.
- Use certified marine-grade fuel additives to prevent carbon buildup.
- Ensure proper warm-up and cooldown cycles to avoid thermal shock on injector tips.
- Keep a spare set of pre-tested injectors on board. Swapping during routine downtime prevents being stuck mid-voyage due to clogged nozzles or timing issues.
Bottom line: Fuel injectors operate in a brutal environment — and small problems cause big losses. Keeping fuel clean and monitoring injector wear are critical to performance, economy, and compliance.
8️⃣ Stern Tube (Shaft) Seals (expand)
Stern tube seals surround the propulsion shaft where it exits the hull, preventing seawater from entering the vessel and oil from leaking out. They are a critical part of the shaft-line system and essential to both propulsion and environmental compliance.
⚠️ Why It Fails:
- Seal lip wear from constant shaft rotation and vibration.
- Misalignment of the shaft causing uneven wear or deformation.
- Dry running due to loss of lubrication or cooling water.
- Aging rubber elements or poor material compatibility with lubricants.
- Seal replacement (in dry dock): $15,000 – $50,000 depending on ship size and access.
- Emergency repair at sea can be extremely complex and costly.
- Oil leakage can lead to MARPOL violations, fines, and reputational damage.
- Monitor stern tube oil levels and pressure regularly — sudden drops may indicate a leak.
- Schedule routine shaft alignment checks to minimize uneven wear on seals.
- Replace seals proactively during dry dock rather than waiting for signs of leakage.
- Use environmentally acceptable lubricants (EALs) when required by port regulations.
- Install a leak-detection system with an oil-water interface alarm. This provides early warning before seal damage leads to a larger spill or operational issue.
Bottom line: Stern tube seal failures are silent at first — until they become legal and mechanical emergencies. Preventative alignment, lubricant monitoring, and timely replacement are key to keeping the shaft line tight and compliant.
9️⃣ Bilge Pump Motors (expand)
Bilge pump motors power the system that removes water from the lowest points of the vessel. They are vital to keeping the engine room, shaft tunnels, and other compartments dry, especially during heavy weather or in the event of a leak.
⚠️ Why It Fails:
- Motor burnout from continuous or overloaded operation.
- Electrical faults from water ingress, poor insulation, or corroded terminals.
- Jammed impeller or clogged strainer restricting water flow.
- Float switch failure causing pumps to run dry or not activate at all.
- Standard motor replacement: $3,000 – $10,000 depending on size and type.
- Emergency in-port service and re-priming can add $5,000+ in labor and port fees.
- Failure during bad weather or after flooding can result in critical water accumulation and stability risks.
- Test pump and float switch operation weekly, especially before departure.
- Clean strainers and check for impeller obstructions regularly.
- Ensure proper grounding and inspect motor housing for rust or water exposure.
- Label emergency manual switches and confirm crew knows their location.
- Install a runtime meter on each bilge pump. Unusual increases in pump activity often signal a leak or a developing issue before it becomes critical.
Bottom line: A failed bilge pump motor is a silent threat until you need it most. Staying ahead with frequent testing and clean electrical connections can prevent dangerous flooding and save your ship from a preventable emergency.
🔟 Air Compressor Piston Rings / Air System (expand)
Air compressors provide the starting air required to crank main and auxiliary engines. The piston rings inside the compressor maintain compression and separate oil from air. When these wear out, the entire starting system is at risk.
⚠️ Why It Fails:
- Ring wear from high temperatures and continuous duty cycles.
- Oil carryover contaminating air lines due to ring blow-by.
- Poor-quality lubricants or infrequent oil changes leading to excessive friction.
- Moisture in the system causing rust and pitting on cylinder liners and pistons.
- Piston ring set: $2,000 – $5,000 per compressor.
- Complete compressor overhaul: $10,000 – $25,000.
- Failure to start main engine due to air issues can result in port delay fines or tug costs.
- Drain moisture from air receivers and lines daily, especially in humid environments.
- Monitor oil consumption and discharge pipe residue — oily exhaust often signals worn rings.
- Change compressor oil as recommended and use only approved grades.
- Inspect air intake filters and check for restricted flow or debris buildup.
- Use a dew point meter to track moisture in the compressed air system. Unexpected spikes often mean ring inefficiency or incomplete compression — and give early warning before failure.
Bottom line: Starting air isn’t optional — and piston rings are the linchpin. Monitoring compressor performance and replacing worn rings before they fail can keep your engines turning when you need them most.
1️⃣1️⃣ Hatch Cover Rubber Seals (expand)
Hatch cover rubber seals form the watertight barrier between the cargo hold and the environment. These flexible gaskets are critical for keeping seawater out and protecting dry cargo, especially on bulk carriers and general cargo ships.
⚠️ Why It Fails:
- Compression set over time from repeated hatch closures.
- Weather exposure causing hardening, cracking, or UV damage.
- Improper cleaning or chemical contamination degrading the rubber compound.
- Misaligned hatches exerting uneven pressure on sealing surfaces.
- Seal kit: $8,000 – $20,000 depending on vessel size and number of hatches.
- Water ingress can destroy cargo and trigger claims totaling hundreds of thousands of dollars.
- Port state control detention is possible if sealing condition fails inspection.
- Conduct regular chalk tests or ultrasonic leak detection to verify watertight integrity.
- Clean seals and contact surfaces routinely to remove grit and debris.
- Apply silicone or compatible rubber conditioner every 3–6 months to maintain flexibility.
- Replace entire lengths of seal rather than patching for long-term performance.
- Carry a portable ultrasonic hatch cover tester onboard. Early detection of compression loss or sealing gaps can prevent major water ingress — and failed PSC inspections.
Bottom line: Hatch cover seals are low-cost parts with high-stakes consequences. Keeping them supple, clean, and well-fitted is essential to protecting cargo and staying compliant on international routes.
1️⃣2️⃣ DP System Valves / Sensors (expand)
Dynamic Positioning (DP) systems use thrusters, sensors, and automated controls to keep a vessel fixed in position without anchoring. This is essential for offshore supply vessels, cable layers, drillships, and other precision-based operations. The valves and sensors within these systems are the most common failure points.
⚠️ Why It Fails:
- Hydraulic valve sticking or leaking due to contaminated fluid or seal wear.
- Sensor drift or failure from heat, moisture, or electrical surges.
- Software-to-hardware mismatch during firmware updates or retrofits.
- Inconsistent calibration or dirty feedback signals from motion/reference sensors.
- Individual sensor or valve: $2,000 – $10,000.
- Full diagnostic and DP system recalibration: $15,000 – $40,000.
- DP failure mid-operation can lead to dropped contracts, high tug assist costs, or offshore hazards.
- Flush and replace hydraulic fluid per OEM schedule to prevent valve fouling.
- Calibrate motion, wind, and GPS sensors quarterly — especially after repairs or grounding.
- Test redundancy logic regularly to ensure seamless switchovers between control systems.
- Keep software and firmware updated but validated for your vessel’s configuration before implementation.
- Always run full DP system diagnostics in port before deployment. Minor sensor faults don’t always trigger alarms but can throw the entire system off during offshore work.
Bottom line: The precision of your DP system is only as good as its sensors and valves. Consistent calibration, fluid cleanliness, and system validation are key to holding position — and your reputation — in tough offshore conditions.
Every ship failure has a story and most begin with a part that was overlooked, worn down, or taken for granted. These 12 components aren’t theoretical vulnerabilities; they’re the real-world culprits behind breakdowns, diversions, and six-figure repair bills across fleets worldwide.
Whether you're managing a single vessel or an entire fleet, staying ahead of these failure points can mean the difference between smooth operations and costly downtime. Preventative maintenance isn’t just a checklist, it’s a strategy.
Start with the dirty dozen. Monitor them. Plan replacements before they fail. And when possible, train your crew to recognize the warning signs early. The more you know about what really breaks at sea, the better prepared you’ll be to keep sailing through whatever comes next.
