On Bored/ Board Systems: Electrical Systems

Part I: AC/DC Power


Much of living on a boat (especially living on a boat affordably) consists of maintenance and upkeep – and not the kind of upkeep where you’re happily polishing the brass while whistling a jaunty sailing tune, but the kind of upkeep where you’re servicing engines, monitoring voltage outputs, and repairing faulty electrical wiring.

In sailing couples, the burden of this type of maintenance often falls mostly on one person, while the other crew member just kind of stands there, holding a wrench. While this isn’t always a horrible state of affairs, particularly for the person who has to do nothing, it can be annoying to the more technologically-proficient person to have sole responsibility for every single boring and dirty task essential to marine survival (ask me how I know). More importantly, in the event of an accident, it’s crucial that everyone can operate the boat’s basic systems, or you will be quite literally sunk.

Caution: Benn at Work

So, every once in a while, we will be looking at the basics of maintaining and operating a boat — exciting topics like engine repair, electrical systems, battery maintenance, and so on. Hopefully, we will be able to make them simple and straightforward enough that anyone can understand them in all of their tedious fascinating intricacies.

Which is why some of what we cover will probably seem obvious to a lot people. In fact, Benn told me that most of this post sounds really patronizing; after all, he said, everyone knows the difference between AC and DC power. While that may well be true of many people, even after 2 years of living aboard a narrowboat, I still had no idea what Benn meant when he talked about our AC and DC systems. And, after a very brief poll of non-boaty people, I found that 3 out of 4 people actually do not know the difference between AC and DC power — and the one who does is an oil and gas lawyer who sometimes has to talk to scientists. (Yes, the poll consisted of only 4 people.)


If you are not an oil and gas lawyer, scientist, or mechanic and have always lived on land, diesel generators and battery loads are probably irrelevant to your life. A house won’t be bowled over by an oil tanker if you fail to turn on the lights at night, and if the electricity happens to go out, it’s either because you forgot to pay the bill or the electrical company screwed up. Either way, you’re unlikely to be stranded in a watery wasteland, facing imminent death because of it.

So, here we go. Feel free to add corrections, amendments, or additional insights in the comments.

On Board Systems: Electricity

You use electricity on a boat for many things, such as:
– starting the engine
– operating navigational systems, like your GPS
– autopilot steering
– navigational lights
– desktop computers
– charging mobile phones, laptops, or other small gadgets
– interior lights
– heating and cooling
– appliances, like mixers, washing machines, toasters, icemakers, and hairdryers
– electric winches

Some of these are very important, others not so much. Part of using electricity responsibly on a boat depends on setting priorities and differentiating between what is important and what isn’t. Hint: if you need it to start, navigate, or sail your boat, it’s important. If you need it to make your life easier, more convenient, or more glamorous, it isn’t.

AC and DC systems

The Power Plant, Home of AC Power

The most important thing to understand is that you actually have two different electrical systems on your boat: AC and DC.

As you probably remember from school, electricity is transmitted in the form of a current which flows from a power source (like a power plant or a battery) to a power outlet (like the outlet in your house or the cigarette plug in your car). This current will either be AC (alternating current) or DC (direct current).

A Battery Bank, Home of DC Power

There is no reason to get too technical about the differences between the two. You can read all about it elsewhere. Suffice it to say that AC power is the type of power you get out of the electrical socket in your house or a mainland shore hookup. Unless you are really into eco-living or exist on the cutting edge of technology, AC power is probably what you use in your house to run all of your appliances and other things that make life pleasant and convenient: washing machines, electrical stoves, televisions, air conditioning systems, etc… DC power, on the other hand, is the type of power you mostly get from batteries. For example, your car uses DC power stored in a battery to start the engine, run the interior and dashboard lights, and charge your phone off of the USB outlet. In fact, anything that runs off of a battery, like small appliances or even your computer, uses DC power to operate.

You don’t have to become an expert on electricity to understand how to operate the AC and DC systems on your boat, but a general concept of how they work will help you maintain your systems better and use them more responsibly. You will also be less likely to run out of power or have a massive electrical fire.

Energy Supply and Power Sources:

There are three main sources of electrical power on a boat:

1) Batteries
2) Electrical hookups on shore or at a marina (shorepower)
3) Alternative sources like generators, solar panels, or wind generators

Some of them, like shorepower hookups and AC generators, supply AC power, while others, like the batteries or wind generators, supply DC power.

Since AC and DC currents travel through different cables, each has its own system, with its own demands, advantages, disadvantages, and headaches.


For our purposes, the most significant difference between AC and DC power is their different voltages.

Not so sure we need these anymore.

A volt (V) is just a measure of the strength of the electrical current. Your DC system usually provides 12V (which is why it’s sometimes called a 12V system), while your AC system provides 120V in the USA or 240V in Europe. AC power is “stronger” (i.e., it has a higher voltage) than DC power, so it can be used to power many things that DC can’t, like the electric chair. (If you want to know more about AC power and the development of the electric chair — and who wouldn’t? —  you can read all about it in our next post, which will contain almost no information that has to do with boats.)

Don’t know what this says, but it’s probably good advice.

Countries supply different voltages of electricity through their AC systems, which is why an electric razor that works in America will be totally fried if you try to plug it in in Europe. It’s best to check out the voltage of the AC power before you hook up your boat to the shorepower when you’re in another country, or you could end up blowing your system and your appliances.

(Interestingly enough, it was thanks to Mr. Thomas Edison and his safety conscious approach to domestic electrical systems that the US has a much lower mains power voltage than other countries. Not to worry, history haters. I’m saving all that talk of Tesla and Edison for the next post.)

Advantages and Disadvantages of AC and DC Power

The differences in the strength of their currents mean that AC power can do some things that DC cannot and vice versa. Each of these systems has its own advantages and disadvantages — and you must keep them in mind if you hope to keep your boat’s electrical system in order.

AC power: Advantages and Disadvantages

AC power can be used to run most of the appliances on your boat that make your life easy and enjoyable, like:

— air conditioning
—desktop computers
— kitchen appliances like mixers, toasters, icemakers
— washing machines
— hairdryers
—power tools
—other things I can’t think of because we aren’t allowed to have them (We use AC appliances very rarely.)

AC power is also used for charging your batteries, which is very important.

Massive Generator

The main advantage of AC power is that its higher voltage means that it can be used to run higher voltage appliances. The main disadvantage of AC power is that it requires a constant supply of fuel to be generated, meaning that you always have to be hooked up to a power source in order to use it. For boats, this power source is usually provided by a shorepower hookup, unless you have an AC generator or an inverter.

Tiny Inverter

While, unlike shorepower, both generators and inverters can be used while you are underway, neither is a perfect source of AC power. AC generators, for one, run on gasoline or diesel, which means that you have to keep a lot of heavy, flammable, smelly, toxic materials aboard your boat just to power your immersion blender. Inverters, on the other hand, actually run off your batteries and are therefore way less annoying. (For those who, like me 2 years ago, don’t know, inverters are magical little machines that take DC power from your batteries and convert it into AC power, allowing you to use small appliances and charge your laptop computer when you aren’t hooked up to the shore.) Before you get too excited, however, it’s important to realize that inverters aren’t really strong enough to power everything, especially big appliances. And, even tiny appliances will place a huge strain on your batteries and decrease their lifespan. If you want to spend a lot of money, you can buy a fancy inverter that transforms the AC power back into DC power to recharge your batteries, thereby reducing the damage they cause to your batteries, but they’re still not as effective a means of preserving battery life as just not using an inverter at all.

The sad truth is that AC power is not all that efficient on a boat — which means that most AC-powered devices, while convenient, are way more hassle than they are worth. We try to have as few of them as possible. This means some tiny sacrifices in comfort, which are nevertheless hugely compensated for by all of the thrill and excitement of living on a boat.

DC Power: Advantages and Disadvantages

DC power is used for most of the essential electrical stuff on your boat, such as:

– starting the engine
– operating navigational systems, like your GPS
– autopilot steering
– navigational lights
– interior lights
– electric winches

It has the advantage of being able to be stored in batteries, which means that you can use it when you’re cruising, and, because the batteries recharge themselves, you can have a constant power supply over a long period of time. DC power is portable and renewable and, unlike your AC system, your DC system is more or less self-sustaining — until your batteries die, but we will talk about that more in a future post on batteries.

There’s another advantage to DC power: it can run off of alternative (re: free) sources of energy, like solar and wind power. That means that in theory you can charge and recharge your batteries off of nothing but the sun and the wind — and avoid paying obnoxious marina fees altogether.

There are also marine versions of lots of appliances, which run off of DC power. However, they are mega expensive to buy and repair and still not all that great for your batteries. It’s probably best to forgo them altogether. I mean, do you really need an icemaker on your boat? Probably not.

The future is now!

Interestingly enough, some people now believe that the future of home power lies in DC power — namely, in large battery storage banks which harness alternative forms of energy and use them to power all home appliances. Tesla in particular is exploring home energy storage, which is sort of funny, as Nikolai Tesla, for whom the company is named, was an early proponent of AC power and instrumental in designing technologies that made AC power safe and practical for home use.

Which, surprise, surprise, you can read all about in our next post, featuring an historical tangent entirely unrelated to boats.

While this post may have been a waste of time for the more mechanically-inclined, I hope that those of you who are as ignorant regarding STEM technologies as I am found it at least a bit useful. There is lots more thrilling stuff to know about your electrical system, and we will continue writing on this topic in equally thrilling posts in the future.


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