Choosing the Right Marine Generator For You

May 10, 2017 - 9:00 AM by Samantha Pudney


Today’s marine vessels brim with power-hungry electrical equipment, from the latest audio systems to air conditioners. Supplying enough current for all of these accessories can pose a challenge at the best of times.

Even on a small boat, you will need a marine generator to run many of your accessories. Marine generators can be a major investment. After your main engine, it is usually the most expensive piece of equipment aboard.

Choosing the right marine generator for you is an important decision. You’ll want a generator that is reliable, offers longevity and delivers a comfortable time on board. Whether you’re adding, upgrading or ordering a new boat, here are a few things to ask yourself:

1. AC or DC?

Since alternating current (AC) is well-suited to power distribution. AC marine generators are the standard today. Generators that produce direct current (DC) are almost non-existent in the current marine industry. As a sparse alternative, DC can be difficult to find and expensive.

2. Inverter or Generator?

Inverters change DC power from your battery bank into AC power to run your AC equipment. Inverters work well for boats that only require small amounts of power over a short period of time. If you have a large boat, the consistent power demands and electric motors may require a marine generator and an inverter.

3. Engine, Hydraulic Drive or Both?

Hydraulic drive marine generators are best suited to boats with small, intermittent power requirements. As a general rule, it is best practice to rely on a hydraulic generator only when small amounts of power are necessary. This is because operating the main engine just for electricity is inefficient.

4. Operating Speed

Electronic equipment is designed to use power with a fixed frequency, measured in hertz (Hz). Europe, Australia and much of Asia use 50 Hz. Choose the frequency used in the region where you will get the most use out of your boat.

The frequency output of a generator depends on its fixed engine speed. To produce 60 Hz of electricity, the engine operates at 1200, 1800, or 3600 revolutions per minute (rpm). 50 Hz machines run at 1000, 1500 or 3000 rpm, which has its advantages and drawbacks.

Four pole generators, running at 1800 rpm for US power standards or 1500 rpm for European standards are most common. They offer great benefits being fuel efficient, quiet, inexpensive and reliable for a long haul trip.

5. Petrol or Diesel?

When you need to decide between a marine diesel generator or a petrol generator, check to see which your main engine uses and match it. Keep in mind that the explosive nature of petrol requires a spark-free generator.


6. Cooling Systems: Heat Exchanger, Keel Cooled or Seawater Cooled?

Liquid cooled generator engine are engineered to be used in a marine environment. They are available in three configurations: heat exchanger, keel cooled or direct seawater. Your marine generator should have the same type of liquid cooling as your main engine.

Keel cooled generators require their own keel cooler so they are not tied to the main engine’s grid. Direct seawater cooling systems pump seawater through the engine, and generators that are heat exchanger cooled feature two cooling water circuits. These move the coolant through a cooling grid on the bottom of the boat.

7. Temperature Rise

When carrying a full load, a generator’s copper windings heat up. The difference between the temperature of the ambient air and the windings is called ‘temperature rise.’ It indicates the quality and quantity of copper in the marine generator.

The lower the temperature rise, the higher the copper content and the better the quality. Marine generators should have a temperature rise of 95 to 105ºC. This is particularly important if the generator will be operating in hot engine rooms.

8. The Right Size Generator

Selecting the right kilowatt size marine generator for your boat is an important decision. If you choose a generator that is too small, it will wear out faster, produce excessive exhaust smoke and can potentially damage other electrical equipment.

On the other hand, if it is too large then it will run under-loaded. This can lead to carbon buildup on the cylinder head, leave unburned fuel in the exhaust and contribute to inefficient operation. It is best practice to never allow a generator to run with less than a 25% load.

9. Estimating Your Load

It is best to have your authorised generator dealer perform a load analysis of your boat to determine the right size generator required. They will start by asking for your estimated wattage load. Depending on the size and quality of the motor being started, the amount of power necessary to start the electrical appliance can be up to ten times its running wattage.

This is why it is crucial to supply your dealer with both the starting and running wattages of each motor. They can then calculate the electrical load of all the equipment you will run at any one time.