A large percentage of recreational boats over 28 feet (8.53 meters) in length, as well as work craft of all different sizes, carry marine generators to provide electric power to various boat systems and accessories. A marine generator, while not an absolute necessity, is handy to have in circumstances where the main engines are shut down or shore power is unavailable, i.e. anchored at sea. This alternate power source saves battery power and uses considerably less fuel than the main engines.

The typical marine generator, like all mobile generators, burns either diesel fuel or gasoline. A diesel powered boat will, therefore, ordinarily carry a diesel generator, a gasoline powered boat, a gasoline generator. The power generator on a boat will typically be tied into the vessels engine fuel line, thus negating a separate, space-consuming fuel tank.

Marine generators come in all sizes and are usually rated by the amount of kilowatts of electrical current that each produces, a kilowatt being a thousand watts. Smaller recreational boats may require a generator capable of no more than three kw while larger, recreational or working boats, such as luxury yachts, fishing vessels, ferryboats, and harbor tour boats often have generators of 25-plus kw capacity on board. A boat owner considering an electric generator would be well advised to total up the wattage usage for all appliances, instruments, and systems anticipated to be powered by the generator, then consult to ensure the right marine generator is chosen for the particular boat.

A marine generator differs from the ordinary residential or industrial generator in that it is designed and constructed to withstand the moisture and corrosion problems associated with the marine environment. Additionally, the vast majority of marine generators don’t need a self-contained cooling system, being cooled instead by hydraulic pumps constantly circulating seawater through the generator core. Thus, a marine generator will take less space in the usually cramped engine spaces of the typical recreational or work boat.

Beware of confusing an inverter with a marine generator; each is a separate electrical power producer. An inverter will convert a vessels battery power, which is direct-current (DC) into a weak alternating-current (AC) to provide power. A generator, on the other hand provides constant AC electricity independent of the batteries. This can be a serious consideration when attempting to start an inverter-equipped boat with drained batteries.