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Don't Let Neglected Maintenance Sink Your Boat Generator

Routine maintenance is critical when it comes to reliability and extending the service life of your generator. Here's what you need to know.

White boat generator with varies wires and hoses attached to it sits in a wooden cabinet

Photos: Frank Lanier

The harder it is to conduct maintenance, the greater the chance it will be deferred. To avoid this, generators should be located so that maintenance can be done easily, without the need for major acrobatics or equipment removal. Today's generators are extremely compact and can be installed in limited-access areas. Most have all service points located on one side, which not only makes maintenance easier but saves space by letting you install the generator next to a bulkhead without losing accessibility.

Despite (or perhaps because of) this compactness and the new installation options it provides, some installations push the boundaries of accessibility to the point of absurdity. As a marine surveyor, I see generators tucked in such out-of-the-way places that it's barely possible to check the engine oil, much less conduct maintenance or basic repairs, such as swapping out a raw water pump impeller or changing a broken drive belt.

In extreme cases, routine maintenance can only be conducted by removing the generator for servicing, a worst-case scenario that virtually guarantees maintenance will be deferred or nonexistent — something that must be considered when purchasing a boat or developing a maintenance plan for your current one.

Two Different Systems

Although collectively referred to as a generator, or "genset," a generator can be divided into two separate systems: an engine (which provides the power to run the generator) and the generator itself, which converts the mechanical energy of the engine into electrical power. From a maintenance perspective, care of the generator engine is similar to your vessel's primary engine; generator maintenance requirements align with requirements for electrical equipment (such as an alternator or electrical motor). Much has been written about engine maintenance (gas and diesel), so let's concentrate on the generator itself.

While you'll always want to reference your genset owners manual for specific maintenance requirements and procedures, here are some basic tips that can be applied to most any generator. It is not intended to be all-encompassing, but rather a starting point to aid in developing your own routine maintenance schedule.

Boat generator installed with a white sound shield with gray hose coming out the left side

Generators must be located to facilitate ease of maintenance. This generator location and sound shield will make inspection very difficult and a lot of work.

Removing white sliding panel from in front of boat generator

Periodically remove inspection panels from enclosed generators (or the entire sound shield) to facilitate routine inspections.

Generators are often enclosed in a sound shield. If so, it's critical to periodically remove inspection panels from the shield (or perhaps the entire shield) and thoroughly check out both the engine and generator units, including:

  1. Test and verify operation of all warning alarms, such as oil pressure, temperature, and any safety shutdown alarms — particularly important, as the sound shield may obscure components from easy viewing.
  1. Start the generator and listen to it (while loaded and unloaded) for unusual sounds that may otherwise be obscured by the sound shield.

Start-Battery Inspections

Your generator should have a dedicated start battery, which ensures that it can be started regardless of house or engine battery/bank voltage levels. The battery should receive charging from the generator when it's running, and from your battery charger when it isn't. Battery installation and maintenance is similar to that for your engine starting and house batteries.

Boat generator start battery with white corrosion growing on the battery terminal

The generator start battery requires routine maintenance to avoid this kind of corrosion damage.

Generator Maintenance

The actual generator is an arrangement of wire windings and a magnet, with the engine rotating either the magnet or the coil, depending on the type of generator. Put simply, when the magnet rotates within or around a coil of wire, the magnet pushes electrons through the wires, creating electricity. There are numerous variations of this and numerous other components that make it work.

While much generator maintenance may be beyond the scope of a nonprofessional, some maintenance can be easily performed by any competent DIY-er. Regardless, have a general understanding of what's going on, and learn to make observations to assure that you properly perform the needed maintenance yourself, or have it performed by qualified professionals.

Generator Electrical Inspections

Start by looking for issues such as loose or corroded connections, overheating wires, or problems such as corrosion, charred terminals, broken wires, or exposed conductors. Check generator circuit breakers by flipping each individually with the generator off while checking for play or looseness.

Generator Output Checks

Generator operation should be verified prior to starting a cruise — or at least quarterly. Operational checks should include monitoring output voltages and hertz while unloaded and when placed under a moderate to heavy load once the generator is warmed up. Most pleasurecraft will use a 60 Hz three-phase generator setup to produce 120/208 volts, or a single-phase generator producing 120, 240, or 120/240.

This is the point where the engine comes significantly into play. Rather than just turning the shaft on your generator, it must turn it at specific revolutions per minute (rpm), and this relates to the generator's output. For your propulsion engine, you're accustomed to moving the throttle and having the engine respond to that setting. With a generator, the speed is normally controlled without your intervention. The frequency output of a generator depends on its fixed engine speed. To produce 60 Hz (the U.S. standard), the engine will operate at 1,200, 1,800, or 3,600 rpm depending on the generator. If the frequency output is wrong, you may damage electrical users, especially sensitive electronics. If your system doesn't already include one, you can install a panel-mounted hertz meter or purchase a hand-held unit (many higher end multimeters can also check hertz) and make necessary adjustments in speed or responsiveness according to generator manufacturer instructions.

There are various components (typically called governors) on a generator motor to help control its speed and responsiveness. These components should operate in relation to the generator's output. On some generators, these can be partially adjusted by doing little more than tweaking a throttle spring to the correct tension. Others are far more complex. Improper voltage and hertz readings may be a sign that you have a problem. If there's any question of your ability to do this safely and well, get an ABYC (American Boat and Yacht Counsel)-certified technician.

Main AC electrical panel fro a boat generator

Most generator installations will include an AC volt meter either at the generator, remote control panel, or as part of the main AC electrical panel.

"Voltage regulation" is a term used to describe how accurately the generator controls its output voltage. Externally regulated generators using an automatic voltage regulator (AVR) will produce "cleaner" power in the form of more symmetrical sine waves and closer voltage tolerances. The output voltage of a self-regulated generator (i.e., one without an AVR) will vary to a greater degree. Some voltage regulators can be adjusted or easily replaced (if faulty). This is typically a job for a certified technician. However, knowing the type of regulation you have is helpful.

Knowing the power output of your generator under normal operating conditions (loaded and unloaded) and monitoring it will enable you to more easily spot problems so they can be addressed. Monitor voltage and know what kind of regulation you have.

Follow the specific instructions provided by your generator manufacturer when checking output voltages. Here are the basic steps:

  1. Start the generator.
  1. Check output voltage while the generator is unloaded. To facilitate this, most generator installations will include an AC volt meter either at the generator, remote control panel, or as part of the main AC electrical panel. If not, output voltage can easily be checked with a portable multimeter (see "Checking Generator Voltage Output" below).
  1. The voltage shown should be at or very close to the output being tested.
  1. Place the generator under load by turning on equipment that uses the power output you're testing (such as an air conditioning unit). While the generator rpm might briefly slow down, it should quickly resume speed and maintain the correct voltage and hertz readings.

    Note the voltage with the generator under load and compare with the above no-load reading. The output under load will vary based on the amount of load placed on the generator. But, in general, a 5% or 6% difference in voltages should be considered suspect and investigated.

    A good starting check would be to verify that the engine is operating at the correct rpm. Other possible problems can range from AVR issues (often an AVR is basically a plug-and-play replacement), poor contact between the rotor carbon brush and commutator, or a load that exceeds the generator output.

Checking Generator Voltage Output

You can check your voltage with a portable volt meter or multimeter on a live outlet, but safety first! Start by reading the setup and operating instructions provided by the meter manufacturer and follow all safety recommendations. Modern outlets have three openings: hot, neutral, and ground. The rounded half circle is the ground, the shorter slot is hot, and the longer slot is the neutral.

With the generator running:

  1. Turn on the volt meter and set to the AC voltage, ensuring it's at the proper range being checked (e.g., 120 volts AC).
  1. Insert the red probe in the smaller slot (hot) and the black probe into the larger one (neutral).
  1. Note the voltage.


Determine if your generator has brushes and, if so, check their condition or replace at manufacturer recommended intervals. Brushes conduct the electrical current between the stationary and rotating wires inside your generator motor. They handle a lot of energy and are designed to wear over time. Signs of a worn brush can range from reduced performance and inconsistent power, to sparks or even a burning smell.

The brushes ride against the commutator, which also should be inspected for uneven wear or damage that could occur if the brush is too worn and/or the spring or holder rubs against the commutator. Also, check brush holders and springs (these typically come as a unit). A failed brush or holder can disable your generator and cause problems. Knowing these signs will help you spot problems earlier, allowing you to replace worn brushes and parts before damage occurs. They're relatively inexpensive and often easy to replace. But call a competent, preferably ABYC-certified marine technician if there's any doubt.

Other Checks

A generator produces a lot of heat and, as such, the space it's located in needs plenty of ventilation. When located in an enclosure, it is crucial to ensure ventilation ports, fans, and ventilation ducting (as applicable) remain clean and free from obstructions. Inspect generator wire runs for loose or hanging wires, damaged conductors, and chafe points — particularly where wires pass through soundproof enclosures, bulkheads, or other such partitions. Wiring should be supported at least every 18 inches with nonmetallic supports, except in the engine room where metallic wire supports are required.

Boat generator access below helm

The space a generator is located in should be easily accessible and well-ventilated.

In addition to being a great way to head off potential problems, regular inspections also provide an opportunity to familiarize yourself with your generator installation. Trace out any wiring you're unfamiliar with and take the time to ensure system wiring diagrams are up to date, which will ease troubleshooting and make you more self-sufficient in the event a problem occurs.

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Frank Lanier

Contributing Editor, BoatUS Magazine

Capt. Frank Lanier is a SAMS-accredited marine surveyor with over 40 years of experience in the marine and diving industries. He’s an author, public speaker, and multiple award-winning journalist whose articles on boat maintenance, repair, and seamanship appear regularly in numerous marine publications worldwide. Contact him via his YouTube channel “Everything Boats with Capt. Frank Lanier” or at