Annual yacht generator service checklist: what to inspect

An annual generator service should start with the installed unit's operator manual and hour log, not a generic parts list. The manufacturer may set tasks by operating hours, calendar time, storage history or a combination of these.

This guide explains how to define the work, what the available Cummins Onan guidance covers, and how to verify the generator afterwards. It also separates routine crew checks from work that should go to a trained engineer.

Build the service scope from the manual and hour log

Record the generator model and current hours, then compare the hour log with the model-specific service grid. Cummins says its manuals provide specific directions and intervals in grid form, so the installed generator's documents control the schedule.

Do not assume that every item is replaced annually. In the cited Cummins schedule, the oil and oil-filter task is required at least once a year, with more frequent service in hot weather. Other items may become due at different operating-hour or calendar points for the installed model.

Storage and recommissioning can also change the scope. Cummins' extended-storage guidance covers the seawater side of the heat exchanger and coolant condition, while its recommissioning procedure includes primary and secondary fuel filters, terminals, wire connections and brushes or slip rings where fitted.

Plan this work before the yacht is committed to a trip. Cummins recommends reviewing required filters, zincs and belts at least a week before a trip or guest arrival, leaving time to identify the correct model-specific tasks rather than treating the service as a last-minute oil change.

What the annual checklist should cover

The table provides a planning framework. It does not replace the generator's manual, and a row does not mean that every component requires annual replacement.

Oil and filters need precise identification. Typical Onan maintenance includes oil changes and air or oil-filter changes, but timing remains model-specific. Primary and secondary fuel-filter replacement appears in Cummins' recommissioning guidance, so it should not be presented as a universal annual interval.

The same distinction applies to belts and zincs. Cummins includes them among the services to review before a trip, but the supplied guidance does not establish one replacement interval for every generator. Check the manual and recorded history before ordering parts.

Cooling, impeller and exhaust inspection

Raw-water condition belongs in the annual plan because the strainer directly affects the system. Cummins tells crews to inspect and clear seawater strainers before they clog and links strainer blockage with impeller damage. The manual for the installed model should decide whether impeller work is due, rather than an assumed annual replacement rule.

For an Onan unit going through extended storage, Cummins directs the seawater side of the heat exchanger to be drained and cleaned. Excessive scaling requires professional cleaning. This is storage guidance, not a universal instruction to descale every generator each year.

Coolant treatment also depends on context. Cummins' storage procedure says coolant two years old or older should be drained and replaced with a suitable mixture for the storage temperature. That figure should remain tied to the storage procedure unless the installed model's service grid gives another requirement.

Inspect hose clamps, fittings and exhaust connections during the pre-trip check. The post-service output check should include the full exhaust system while the generator is running. This covers the exhaust elbow as part of the system inspection, but the supplied guidance does not support a blanket annual elbow replacement.

Do not operate the generator with an exhaust leak. Cummins describes exhaust gas as deadly and requires leaks to be repaired before the generator is run again. Soot or another suspected leak indication therefore calls for shutdown and investigation, not another test run.

The general inspection should also record obvious leaks, unsecured items and odd noises in the compartment. For a sound shield, use the installed model's manual to define any specific scheduled work. The available guidance does not establish a universal annual sound-shield replacement task.

Proving the service under load

An unloaded start does not demonstrate that the generator can produce rated output. Cummins' post-service procedure calls for load to be applied progressively until the unit reaches full rated output, with the full exhaust system inspected while it runs.

The functional check should also cover controls. After service or recommissioning, make start and stop attempts from every station and record the results. The prescribed loaded run should then be completed by competent personnel with suitable equipment.

During that run, the service information calls for attention to fluid leaks, odd noises and exhaust integrity. High temperature, a repeated alarm or abnormal noise is a reason to stop diagnosis at crew level and call an engineer. The generator shutdown fault guide gives a separate framework for a unit that will not remain running.

Brushes, slip rings, alternator controls and associated wiring are not general visual checks for untrained crew. Where those tasks are due, arrange appropriate marine electrical and electronics work rather than treating a successful start as proof that the electrical side is complete.

What crew can check safely

Crew can prepare a useful brief without dismantling the generator or carrying out specialist testing:

• Update the records. Enter the current operating hours and compare them with the exact manufacturer service grid. If the model, specification or history is missing, record that gap rather than guessing the scope.
• Inspect before the first daily start. Visually check oil and coolant levels, hoses, fittings, the seawater strainer, obvious leaks and unsecured items in the compartment.
• Repeat the general inspection as specified. The cited Cummins schedule requires inspection before the first daily start and after every eight hours of operation.
• Check the controls after service. Make start and stop attempts from every station and log each result.
• Complete the prescribed loaded run. This follows service or recommissioning, but full-load testing should go to trained personnel where crew lack the required competence or equipment.

Do not continue running to investigate a known exhaust leak. The leak must be repaired before further operation.

When to call an engineer

Arrange engineering support when the task exceeds visual inspection, record keeping or the crew's training:

• Exhaust or fluid leakage. Stop for an exhaust leak, or for a fluid leak that crew cannot positively identify and correct safely.
• Abnormal operation. Escalate abnormal noise, high temperature or a repeated alarm rather than continuing the loaded run.
• Specialist scheduled work. Call when valve lash, injection work, brushes or slip rings, alternator or control work, heat-exchanger descaling or full-load testing is due and crew are not trained for it.
• Missing service information. An engineer should identify the correct scope when the generator model, specification or maintenance history is unavailable.
• Unclear replacement decisions. Do not turn a generic annual checklist into fixed replacement intervals for impellers, belts, zincs, coolant or filters. Use the installed generator's manual and operating record.

Blueward Marine provides marine generator service in Mallorca. Submit the model, hours, fault description and photographs through the online service booking form, or call the 24/7 emergency line on +34 971 251 374.