Electricity on canal boats: the basics

It’s not something you have to think about in a house – other than paying the bill – but on a boat, the electricity supply will be something you really have to get to grips with, and in more technical detail than you might expect.

Firstly, the only way to have constant and effectively unlimited electricity on a boat is to plug into the UK mains supply (aka the National Grid) at somewhere like a marina.

Such a “shoreline” connection is nothing more than a length of thick cable plugged into the boat at one end and a stanchion on the marina pontoon at the other. Usually those stanchions will have a meter just like a domestic one, so the marina can charge you by the month for whatever you’ve used, usually in ‘units’ aka kWh.

You might think that as long as you’re plugged in like this, you won’t have any difficulty using any electrical appliances or indeed using multiple devices at the same time – but this is not necessarily the case.

First of all, a shoreline will generally provide substantially less power than is supplied to a house. It’s usually 16 Amps at mains voltage (230V, 50Hz AC) which equals just 3.6kW. A typical house might be fused at anywhere from 60A – 100A which would be 13.8kW – 23kW!

Matters are made more complicated by the way that this supply is wired into the boat, and this varies depending on however the boat was designed or has been modified since being built.

The mains could be piped directly around the boat to standard domestic 3-pin sockets in which case you can use as much as the shoreline can supply; or it might just be used to charge an onboard battery bank from where it can then be sent around the boat from a device called an ‘inverter’. Or there may be a manual switch to choose between those options. Or the battery set-up may have an automatic switchover.

In all cases there will be a limit on the amount of power you can use at any one time. For example, a microwave oven could draw 1.2kW (this is not the same as its cooking power which might be just 0.9kW, that is 900 Watts); a vacuum cleaner could take 1kW and a washing machine could draw 2kW while it heats the water – so if you ran all of those at the same time it would total 4.2kW.

Even running directly from a shoreline, this would trip the breaker on a typical marina stanchion because this is more than it can safely supply (usually 3.6kW as mentioned above). Until you reduced your power use, the breaker would keep tripping.

In practical terms this isn’t too limiting because the times you’d run so many heavy-drawing appliances at the same time should be rare.

However, if the mains on board comes via the batteries and an inverter, then you’re limited to the amount that they can supply and this will likely be less than the shoreline, in some cases, much less.

For example, on my boat, I had an inverter rated at just 1.3kW. This meant that whilst I could run a microwave oven, I wouldn’t have been able to run a vacuum cleaner or a toaster or the washing machine at the same time. In fact, I couldn’t really use anything much else when the microwave was on because it was so close to the maximum.

Furthermore, traditional battery types (lead acid / AGM) drain faster the more power you try to pull from them so it’s generally a kindness to the batteries not to use power-hungry appliances at all.

To the uninitiated, this can all sound a bit daunting and believe me we haven’t even begun to scratch the surface yet. Unfortunately it is a topic you have to come to grips with if you want to live on a boat.

The key point is just to remember that you can’t use electricity like you could at home, and that the supply on board is limited even when you’re plugged into a shoreline.

It gets even worse though: as soon as you unplug and take the boat out onto the canals, you’re reliant on however much power your battery bank can carry before it runs dry. Boat batteries are just like any other battery in that as soon as you start using them, their power starts to run down.

Like your mobile phone, they will need recharging if you want to keep using them and since the batteries are what keep your lights on and water pumps running and so on, you will need them constantly topped up.

Charging can be accomplished in various ways, such as:-

  • From the mains whilst you’re plugged into a shoreline
  • From the engine as you cruise along the canal
  • From solar panels on the roof
  • From a generator, maybe built into the boat or a portable one kept aboard
  • From a wind turbine

Each of these has their pros and cons, of course.

Mains supply

It’s reliable, easy to use – just plug your boat in to the shoreline. The downside is that you’ll have to pay the marina or whoever owns the mooring for the electricity. You will need to have a mains battery charger wired into your battery bank and it’s very, very advisable to have another device called a galvanic isolator or an isolation transformer wired up correctly too (click here for why)

Engine alternator

This is just the same as the way the alternator in a car recharges the starter battery but on a boat it’s also recharging the ‘leisure’ or ‘house’ batteries as they’re called, which are the ones that power devices within the boat.

The upside of alternator charging is that it happens whenever you go cruising on the boat, regardless of whether you’re moving or in neutral gear – as long as the engine’s running, it’s charging.

The downside is that whilst the engine’s running, it’s using diesel fuel which is costly. The engine running is usually noisy. And you have to run for several hours to put the charge back into the batteries.

People with older boats that don’t have solar can often rely entirely on engine charging. You’ll know this because they have a penchant for mooring next to you and then starting the engine at ten o’clock at night (running your engine or a generator between 8pm and 8am when near other boats is actually prohibited because it’s anti-social. This doesn’t stop some boaters doing it)

Solar panels

Solar tech has come a long way in recent years with greater yields from each panel and a much lower cost. That said, a decent solar setup is still quite a financial investment but it really does pay dividends. In my opinion, it is by far and away the best option for power generation on the canals (for domestic use) but there are some caveats.

Solar is entirely silent, which is appropriate for the tranquil canals. It is generating, albeit slowly, from as soon as there’s a certain amount of daylight, right up until the sun’s almost gone down. Once fitted, there’s generally nothing to do, it just sits there and makes free power.

The downsides are the initial cost, that it takes up space on your roof, can look a bit ugly and should really have the panels tilted towards the sun for maximum output so you can end up constantly fiddling with brackets to try to tilt the panels.

Plus – and this is really the kicker – no matter how big the solar array you put on your roof, it’s going to generate next to nothing at all during winter in the UK. There just isn’t the sunshine nor the hours of daylight to make solar terribly useful from mid-November to the end of February.

OK, sure, there will be occasional glorious days over winter but even then it’ll be for just a few hours on maybe one day every now and then. You will need an alternative source of power over winter, believe me.

For many boaters that’s the engine or a generator, others simply buy a marina mooring over winter and plug into a shoreline simply for the convenience of having all the services they need in the gloomier and colder months.


Portable ‘suitcase’ generators from the likes of Honda are very popular with many boaters. The Honda ones in particular are (relatively) quiet as soon as you get a few feet away from them, can be quite compact and easy to start.

The downside is the initial cost (cheap generators exist but are likely less reliable long term and certainly more noisy which may annoy you and will certainly annoy your neighbours) and the ongoing cost of petrol.

Plus you need to have somewhere safe on board to store the petrol (a vented locker, separate to the gas locker, is ideal) and you’ll need to go ashore and trudge up to a roadside petrol station to top up regularly because petrol is rarely found at canal marinas and wharfs (it’s more readily available at river marinas due to the popularity of cabin cruisers with petrol outboard motors though)

Portable generators are also a magnet for thieves which is why you tend to see them stored on boats with incredibly thick chains as a security measure.

Diesel generators exist too of course and are the best option but they’re absurdly expensive and typically not portable.

Wind turbines

You do see these about but they’re fairly useless on the canals. Put one on a sailing boat on the open ocean and they might work but on a tree-lined canal with barely a breeze, they hardly every fire up.

Even when they do get moving, you need a sustained and high level of wind (30mph plus) to get any useful output from them. At that rate they can be rattly and noisy on your roof.

Plus you’ll have to mount them on a sturdy and tall pole which will need to be taken down whenever you move the boat, else it’ll get ripped off at the first bridge or tunnel you go through. In short, not worth the money or effort.