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© 2019 by UK Marine Electronics Ltd

How to Wire a Boat

OK so the picture on the left is a bit more than basic but we all have to start somewhere!!!

Boat wiring is very different from wiring your car or home.  Basic boat wiring isn't that difficult if you use the right materials & techniques and seek advice from an expert. 

If you are planning a basic 12-volt system, why not have a go yourself? If you need something more complicated, you will probably need help with the design. We offer a full consultation and design service if your project is advanced.

So, let’s get started. First thing is to understand the basic circuits. Unlike houses and cars boats must work in a hostile environment. Let’s face it the minute you leave the dock you are on your own. So, at the very least the on-board electrics need to make sure you can call for help, pumping out water is quite handy, and then the essentials like making sure the fridge works so you don't end up with warm beer.

The basic 12-volt design needs to cater for the following things.

·         A way of making electricity.

·         A way of storing electricity.

·         A way of making sure that electricity is available for the important stuff like calling for help.

·         A way of making sure electricity is available for the pretty important stuff, like your boat not sinking, even when you are away.

·         A way enjoying that cold beer without messing up the two things above.


There are of course lots of other things on boats but then it gets a lot more complicated, we can look at those another day.


Assuming that your boat has an engine, you will need power to start it. For this you will need a battery. There are lots of different types of batteries but for our simple wiring lets choose a Marine Grade lead acid battery.  Don’t go for a car battery it won’t last long on a boat. Its not a good idea to use the engine battery for other stuff on board. Apart from nasty electrical spikes that can damage sensitive electronic the last thing you want is to end up with a flat battery at sea.


The fact that you have an engine means you can make electricity using the alternator. There are lots of other ways of making electricity from solar panels to generators, wind turbines to battery chargers, but we are looking at basics here.


So, the next thing we need to do is store the electricity. This is done in another battery called a service battery. This is a different type of battery, whereas the engine battery can deliver a lot of power in a very short space of time the service battery needs to deliver a lot less power over a much longer period. With the engine battery we are only interested in the amount of power it can deliver in a short period (Cold Cranking Amps or CCA), with the service battery we are interested in how much energy it can hold. Think of it as a bucket of electricity, the more Ampere Hours (AH) the bigger the bucket. Be careful though the AH quoted isn’t the useful amount of power. Roughly speaking a 100AH Lead Acid battery will have about 30 AH of useful power, whereas a Lithium will have 80AH of useful power. That’s another story for another day.


Now we have made and stored the electricity we need to make sure it goes to the right places. The most important electrical thing on the boat is of course the beer fridge. At least I wish it was. The reality is a little less fun.  It is of course the VHF radio. When things start to go seriously wrong the ability to call for help is vital.  So here we need a device that makes sure that power from both the engine and service batteries is available for the VHF. It doesn’t really matter if all the batteries go flat just as long as you can call for help. 



Next is the pretty important stuff. This is usually the bilge pump. This need to work even when the batteries are turned off. So, we have a special circuit called “always on” This works even when the batteries are turned off. It can also be used to power less important stuff like the stereo memory. Of course, it is possible to flatten the battery if the pump keeps turning on, but if the boat sinks you might have to buy a bit more than a new battery.


Now back to the cold beer. You can survive, without the cold beer (just), and cabin lights, so we need a device to switch off the non-essential services when the battery gets low. We have a really clever device for that. It protects your battery, can be used as a battery switch, stops overloads, you can even switch the power on and off from your phone via Bluetooth.


We produce a kit that contains all the components to safely wire a 12-volt system, along with detailed instructions. This is available from UK ENERGYHUB.


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