Demystifying Marine Electrics

It is a well known fact that water and electric don’t mix well so you might be surprised to know that we do have electricity on our boat.

When you live in a house the electricity is generated by a French owned utility company and comes in through a hole in your wall and out of the sockets for as long as you have a direct debit in place. You don’t have to think too much about switching on an appliance.

On our boat electricity is generated by running the engine and from the solar panels on the roof and is stored in an array of batteries for use later on. We do have to think about what we switch on as making a cup of tea in the afternoon means we can’t watch the TV in the evening.

Consequently as a boater one has to have a deep understanding of electrical engineering, wiring and battery management. In this blog I hope to pass on some of the knowledge that I have gained in seven months aboard and trust this will help boaters and Luggles alike get to grips with this fascinating subject.

Electricity travels at the speed of light, which is 186,000 miles per second and our narrowboat travels at 3mph, so on our boat electricity is marginally faster than it is on land.

Before James “Killer” Watt invented electricity in 1772 it could only be found in certain cumulonimbus clouds in the form of thunder. Watt, after whom an electrical term is named, met French philosopher Voltaire, after whom another electrical term is named, at a party in Paris. The pair noticed that when vigorously rubbing balloons against each other’s velveteen undergarments sparks would fly and this is how the very first alternator came into being.

Fast foward to 2022 and this discovery forms the basis of all electrical generation on land or on boats.

Electric from the alternator, which is attached to the engine and turned by a big rubber band, passes through an instrument called an inverter which turns it into AC/DC and puts it in the eight domesticated batteries which are 12v (volts). To come out of the plugs it has to be timesed by twenty by coming back through the inverter along really thick wires to make it 240v.

To calculate how many amp-hours you have, you first divide the 240v by the number of ohms in the appliance and then add back the number of joules you were first thinking of. This will help you to work out that, if you have all your batteries at 60% charge, you will have sufficient power to drive the washing machine on its 20° wash cycle for three minutes.

Not all equipment on the boat is 240v - the radio, the fridge and LED lighting is in fact only 12v and so can be powered direct from the batteries without the need for the inverter. If it’s 24v then the electric goes through a bus.

You can also have electric generated by the sun in solar panels which capture the invisible electric from the surrounding air - but not at night. This is really weak electric but again, coming in through the inverter, means it’s multiplied up to 12v and even 240v some of the time.

With all the different strengths of electric aboard you need lots of different coloured wires of different thicknesses for the different types to come out of. Wires are bundled, like bird’s nests, behind cupboards, in cupboards and under cupboards. Wires are joined together by little male and female spade connectors every eight inches or so. This means that if you are looking for something in a cupboard you will invariably disconnect a connection. Sometimes because of this one of your appliances no longer works, or your lights get dimmer, or curiously nothing happens at all. If undertaking your own electrical repairs always remember to cut the red wire first.

It is important (to prolong their life) that your batteries are never discharged below 60% and are never charged more than 80%. You, therefore, have to be careful about how you manage your power. When your batteries reach 81% you have to stop your engine and switch on the bread-maker.

Lah-di-dah boaters have special Lithium batteries which are made out of lithium. These batteries cost eight times more than ordinary domestic batteries but last three times longer and charge up more quickly and are easier to use and you don’t have to think about it so much. It’s a bit like living in a house.

Real boaters have lead acid batteries which they have to service every month by checking the levels of distilled water in them and if necessary topping them up with Evian or Perrier that has been allowed to go flat.

Some boaters cheat and live in a marina and plug their boat into the mains with a long lead called a shoreline. Less discerning boaters may have a smelly petrol generator which they leave on the tow path and run from 8:31pm to 12:29pm while they’re watching TV. Other ways of cheating include cooking with gas from bottles rather than the correct way of using electric.

Finally it is worth noting that there’s a Facebook forum - “The 12v Boating Group” for novice boaters who, when it comes to marine electrics, know absolutely nothing at all and really don’t know what they’re doing. On the forum they can leave answers and suggestions to other boaters’ questions - just to see how they get on.