How To Choose The Correct Marine Generator For Your Boat

Inverters change DC power from your battery bank into AC power to run AC equipment. Inverters work well for vessels that require only small amounts of power (1000-3500 watts) for short periods of time, but boats with larger, consistent power demands and electric motors require a generator or both generator and inverter.

So, we want to power our electrical devices without running the main engines. This will save fuel, save engine time, reduce emissions, create less noise and vibration, and is simply a more efficient way to produce electricity. Modern technology provides us with several alternative means to generate current, but for this article we’ll focus on fuel powered generators since they are by far the most common.

A marine generator has many similarities to other types of generators. It is designed to run on fuel types like gasoline and propane and run a number of applications depending on the wattage rating. The obvious fuel of choice will be either the gasoline or diesel in your main tanks for an installed generator. A marine generator should be sized according to the number of appliances, tools, or other accessories that will be using it in order to be safe.

The main difference between marine generators and other types of generators is the design of both outer and inner components. Other generators are not designed to be used near water and can even become less efficient in moister environments like near the ocean or lake. Marine generators are intended to handle use on water.

They are designed outside to better protect inner components from water. Inner components are designed to handle wetter environments and can include hydraulic pumps (PTO for other applications), class H insulation, highly non-corrosive material, and other features designed for sea water use. These are some of the reasons boats require marine generators for electrical power and other types like portable generators will not functions as well or as long.

That being said, I do see, more and more, especially on small power or older sailboats, portable gas generators temporarily lashed on deck or swim platforms. Years ago, while delivering an older sloop, I put a small, portable Honda gas generator in the inflatable and floated it behind us while at anchor. The minimal exhaust and noise floated away on the breeze, and the unit provided economical power for a few essentials like music, lights, and the blender. Much safer and more convenient though, is an installed unit.

The most important thing to consider is size. Selecting the right size generator is critical. If it is too small, it will wear out quickly, produce excessive exhaust smoke, and potentially damage electrical equipment. If it is too large, it will run under-loaded, leading to carbon buildup on the cylinder head, unburned fuel in the exhaust, and inefficient operation. From the information plates on your devices, use this formula to calculate wattage: amps x volts = watts.

Turning on appliances that utilize electric motors produces a current surge which can cause voltage and frequency dips, lights to dim and potential damage to sensitive electronics. Depending on the quality and size of the motor being started, the amount of power necessary to start the electric appliance can be up to ten times its running wattage. This must be taken into consideration for proper sizing. Also, generators should never run with less than a 25% load; 35% to 70% is optimal.

Although air cooled generator engines exist, they are not well suited for use in a marine environment which may include water makers, air conditioners, or refrigerators. Heat overload in a confined space must be a consideration. Direct seawater systems pump cooling seawater through the engine, and it may be possible to shunt water through a main engine cooling seacock to the generator. Remember, corrosion and system contamination problems make direct cooling systems critical for most marine applications, so make sure the water filters and piping are of adequate size.

Generators with in-line engines are easy to install and service. Most two cylinder and large displacement, four cylinder engines are not well balanced and vibrate, although four-cylinder engines with counter-rotating balancing shafts eliminate vibration and provide excellent comfort on board. Three and six-cylinder engines are naturally balanced and smooth running so they are the quietest and produce the least vibration.

Since four pole generators operate at low rpms, the engine needs to produce its maximum torque near or below the operating speed. Automotive engines produce maximum torque at higher speeds. For example, when they run at 1800 rpm, automotive engines are working at a point below peak torque, which will limit the engine’s ability to pick up extra loads.

Engines that are made for heavy-duty, industrial applications offer you the strongest, most reliable low-end torque and provide the power to pick up supplementary electrical loads even when running at full power. Also, look for a design that allows easy maintenance access on one side of the unit. This allows installation close to the hull or a bulkhead and you’ll still be able to service the unit.

Like all combustion engines, marine generators also require safety measures. Marine generators produce exhaust which includes carbon monoxide. Some marine generators do a great job at minimizing the amount produced, but CO is inevitable. Carbon monoxide can build up when the boat is stationary or with inadequate ventilation. Carbon monoxide is a colorless, odorless gas that can lead to poisoning or death. Even when the boat is moving, carbon monoxide can build up in enclosed areas.

Some generators come with automatic turn-off switches for high CO levels. For those that don’t, installing CO alarms to detect buildup can prevent serious injury. Like other engines, marine generators can overheat or short circuit causing damage to the boat and other electrical systems. I highly recommend a monitoring panel (sometimes optional). These panels usually allow remote starting and stopping of the unit, engine operation gauges, monitoring of the current, and often built-in circuit breakers.

Be knowledgeable, be aware, and be safe. Happy boating!