Generator Installation Article From USCG Saftey Circular 80

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The proceeding article was written by Mr. Ralph Lambrecht and appeared in the U.S. Coast Guard Publication,
Boating Safety Circular 80, January 1999, and is in the public domain.

Don't Install Generator Sets on the Cheap

With the proliferation of accessories requiring 110 volt AC electrical power, most people with boats having sleeping and cooking accommodations would like to have a source of such energy. Given that the boat has AC circuit wiring and a distribution panel board installed, the simplest sources are a shore power connection while at the dock and in inverter while at sea. An inverter converts low voltage DC to high voltage AC with reasonable efficiency. This is limited to battery capacity; or, if the engine is running, to the alternator output. This will handle modest accessory loads for a while, but any heavy AC load will deplete the battery in short order. An extra battery is held in reserve for cranking the engine and a battery disconnect/selector switch is almost a necessity.

For heavier loads such as electric stoves, air conditioning, or water heaters, shore power or a seperate source of AC power on board such as generator set is the only way to go. Some larger boats can be obtained with a generator set already permanently installed, using the main engine fuel source. These are comparatively expensive installations running to several thousand dollars or considerably more, depending on output capacity. Even if not so equiped originally, these larger boats may have a space set aside for their installation, usually in the engine compartment. But not just any generator set should be installed in the boat interior. It must be a "marine" generator set; liquid cooled with provisions for exterior discharge of exhaust gases. If installed in a boat using gasoline as a fuel, it must be "ignition- protected": creating no sparks or other sources of ignition that can set off a gasoline vapor explosion. A gasoline generator set, even if installed in a compartment separate from the main engines or fuel tanks, needs to be an ignition-protected type. The carburetor also needs a backfire flame arrester.

Such generators are inherently expensive. Liquid cooling usually means a heat exchanger to separate the engine cooling water from the sea water. Water jacketed manifolds and high rise elbows with water discharge into the exhaust hose are standard. When looking in the many catalogs, that come through the mail or passing through a large hardware store, boat owners will see generator sets with outputs of 2 to 5 kilowatts for prices from $300 to $600, a far cry from a $3,000 built-in generator set. What a temptation: cheap AC power for the boat! Such generators are not intended for installation in enclosed spaces, on land, or on the water, and come equipped with warnings to that effect. Their specifications are: air-cooled, gasoline fuel in an integral tank on the generator set, direct exhaust discharge, and no ignition-protection or back fire flame arrester.

Does that mean that they should never be installed or used on a boat? Not necessarily. The key word here is "on" not "in." Such generator sets are all right when running in the open air above deck. They may be noisy, but they will do the job. A three sided enclosure with a top will shield some of the noise and still allow for adequate air cooling. These would be basically short usage installations, certainly not to be left running for extended periods. The limited fuel tank size would take care of that. They can be one source for restoring a dead battery to life so the main engine can be started- always a secure feeling when you sit at anchor most of the night using up battery power for anchor and cabin lights, alarms and stereo music.

All generator sets need to be used with caution, whether liquid cooled permanently installed in the engine compartment or sitting out on the open deck. Internal combustion engines, particularly gasoline engines, are a source of carbon monoxide (CO). This can have an insidious way of getting back into the boat, even if discharged to the exterior. Wind direction, being tied up next to a dock or sea wall or next to another boat may let CO into the boat through an open port or cabin ventilator. One of the riskiest but common procedures on boats equiped with a generator set and air conditioning is to close the cabin up on a hot night and go to sleep with the generator set and air conditioning on. If doing that, a working carbon monoxide alarm is essential. Even though the engine compartment is separated from the cabin space by a bulkhead, this may not be absolutely vapor tight. If an exhaust leak is present and the cabin is at a slightly lower pressure than the engine space, it can become a serious situation. It's not a bad idea to keep the engine compartment ventilation blower running whenever the built-in generator set is running. It brings in fresh air and purges any fumes from the space.

Editors Note: Extreme care must be used when any amount of gasoline is present on board a vessel. Gasoline vapors can accumulate in low areas such as cockpits, bilges, and boat interiors, even when stowed on deck. Any accumulation of vapors in spaces containing non ignition-protected equipment can be an especially hazardous situation which can lead to possible fire/explosion. Special ventilation requirements must be meet in addition to the precautions outlined in this article in a permanent gasoline engine installation. Consultation with an Accredited Marine Surveyor with regards to an installation such as that of a generator, is recommended to ensure that the installation complies with all applicable safety standards and regulations.

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