Fixed or portable diesel or gas generators are commonly found on medium or larger fishing boats when electricity is in demand. They have low fuel consumption, relatively low noise levels, can be easily repositioned (at least portable versions), for example, on-shore when required, or transported for maintenance etc.
Larger models with remote control and electric starters are preferred for onboard use on larger boats and ships. Output power of fixed and portable generators ranges from 1kW to 10kW, even more. So does their price.
One of the drawbacks of diesel and gas generators is that they don't work when they run out of fuel - which is, of course, logical! :)
It is recommended, if possible, that these generators use the same fuel as the main boat engines - if something go wrong, generator(s) can provide energy for electronics and, perhaps, for electric trolling motor, which if needed, can double as auxiliary engine(s).
Note: if your main boat engine(s) have failed and you can't start them, check the fuel first before using it for powering auxiliary generators. Dirt or water in the fuel can cause internal combustion engines to fail, and the main engines usually have much better fuel filters than engines in power generators. Low quality fuel can be cheap, but it can also cause some real headaches. Stay away from it ...
Power generators can be divided in two groups regarding their main intended use:
- they can be used as 'last ditch' auxiliary units when main battery is empty and solar panels/wind turbines are not available for some reason and main engines are not working, or
- they can be used as onboard power source whenever main engines are not in use and mains power from land is not available. They are used for powering all electrics and electronics onboard the boat/ship.
Things to consider when buying power generator:
- type of fuel - diesel or petrol/gas. If your boat is using diesel fuel, perhaps it is better to buy diesel power generator, thus avoiding various types of fuel onboard your vessel.
- engine type - 2-stroke or 4-stroke engines. 2 stroke gas engines use fuel mix (fuel + oil), they are not as efficient as 4-stroke engines, but are simpler and more robust. Exhaust gases from 4-stroke engines are less 'smelly'.
- noise and vibrations levels - noise is measured in decibels (dB) and it represents noise level some distance from the power generator. 60 dB some 20-25 feet from the generator is acceptable.
- required maintenance - modern portable generators are usually low maintenance units, but they must be serviced periodically in order to be ready to operate when required. If they are used as auxiliary power units, their maintenance intervals depend on their usage, similar to the main engines.
- physical dimensions (width, height, length, weight) dictate if the unit can fit into the planned area. Also, heavier units are harder and more difficult to be moved around, if required.
- maximum power determines maximum starting power which unit can provide to the system for shorter period of time. Maximum running power is the power which unit can provide to the system as long as there is fuel available.
- onboard fuel capacity determines the amount of fuel stored in the generator's tank and is given in gallons/liters/ounces AND the length of operating time under certain load (for example, 8 hours under 25% load) per single full fuel tank.
- price of the unit - larger units with stronger and more efficient engines cost more. Also, the more features unit has, the higher the price. Fortunately, when maintained properly, these units last for a long time.
Of course, there are many other features which determine the right power generator for certain situation: onboard charging controller compatibility with the boat electric system, types of power outputs (12V, 24V, USB charger, 110V AC, 220V AC, single phase, three phases etc.), amount of voltage distortions if AC output is available (3% is good, pure sine is even better), connecting two power generators in parallel option, etc.
Long story short - write down what you want and in the end, require, from your power generator and check which one best fits your needs.