I’ll cover outboard motors further down the page but the de facto powerplant for a modern narrowboat or widebeam is the inboard diesel engine. Known for long reliability and substantial torque at low revs – exactly what you need for a heavy, slow-moving boat – the diesel engine is ubiquitous.
Usually consuming around 1 to 1.5 litres of fuel per hour, it’s relatively parsimonious and the engine usually does triple duty not only propelling the boat but also heating the domestic hot water and recharging the battery system.
Marine diesels are “marinised” versions of land engines; in other words a specialist company takes an off the shelf engine and makes various small tweaks to make it better suited to boat use.
Common brands you will see these days include Beta Marine; Barrus Shire; Vetus; and Canaline. Makes that are found in older craft include Lister-Petter; BMC; Nanni; and Isuzu. Plus you find vintage units from the likes of Gardner, Bolinder and Russell Newbery.
By and large these engines are trouble-free (though compared to the engine in a modern diesel car, they do seem amazingly antiquated) and will only require regular servicing to provide long life.
They’re “inboard” engines, that is, installed inside the hull usually under the rear deckboards; contrast this with the outboard motor you’d often find on a fibreglass cruiser for example, which is clamped to the outside of the hull, pushing from the very back of the boat.
Whilst you can get powerful and large outboard motors, they tend to be more about speed than torque and it’s the latter a narrowboat needs; plus outboards almost universally run on petrol which is not widely available along the canal network and is substantially more dangerous to store than diesel. Escaped petrol fumes are an explosion risk, diesel is relatively harmless stuff.
A few, small, narrowboats (maybe 25 feet or less?) have little petrol outboards but they’re the exception. That said, many fibreglass cruisers do use petrol outboards – it’s more common on the rivers than the canals and that’s what those cruisers are generally intended for.
For many narrowboat owners, a boat just isn’t right unless it has a vintage diesel engine contained within a dedicated engine room. These engines are usually massive with a thumping great flywheel, probably one or two cylinders but of huge capacity.
Manufacturers such as Gardner, Lister, Bolinder, Russell Newbery and some even more exotic ones will be whispered reverently by those in the know, who have owners’ clubs devoted to their favourite brand and will spend happy hours polishing the pipework.
Such engines do have a marvellous charm which is a world away from the admittedly somewhat bland experience of a modern boat. They’ll chug over at very low revs, giving a splendid chug…chug…chug which you can not only hear but feel coming from a mile off.
If you want an authentic canal boat experience then this is what you should be after but be prepared to pay for it both in purchase price and in the love and maintenance required.
Something of a polar opposite from such beasts are the increasingly popular diesel-electric hybrid engines which are starting to make inroads. Just as with cars, the future of boating propulsion is surely electric but with limited sunshine in the UK and no canalside charging network, pure electric without any form of additional generator isn’t yet practical.
Thus the combination of a diesel engine with an electric motor plus substantial battery pack (known as “parallel hybrid” because both the diesel and electric motors are able to drive the propeller) gives the option of electric motoring when the batteries are charged, and the diesel engine when the electricity runs out. That diesel will also turn the electric motor which recharges the batteries as you go along. Thus after a while it can be switched off and the boat returned to silent propulsion again.
An alternative form of hybrid, known as “serial hybrid”, has an electric motor as the sole form of propulsion, powered from a substantial battery bank but with a standalone diesel generator recharging it when the battery level drops below a set percentage. The advantage is that a dedicated generator can generally be more efficient at charging than an alternator stuck on a conventional engine, so you should use less fuel, in theory. The downside is that you no longer have the backup of the diesel engine to drive the propeller.
The inevitable question follows – why not just plaster the roof of the boat in solar panels and ditch the diesel altogether?
It’s a nice idea but largely impractical in the UK except for certain cases. If, for example, you run a day-trip boat which will return to a mooring with a mains charging point every night then absolutely, electric-only will work. In fact in that scenario you probably wouldn’t even need solar on top because the boat will only travel short distances and is then recharged overnight.
If you have a boat that’s used only for weekend trips or similar short breaks whereupon it returns to a charging point at a marina or wharf then pure electric is also feasible if you have a big enough battery pack to cover the distance likely to be travelled. A substantial solar array on the roof would, in summer, help to alleviate any need to charge whilst out cruising.
But what about a liveaboard or holidaymaker on a two week break, trying to power by pure electric?
Let’s do some brief calculations. Say you have a small 10kW electric motor. It’ll probably only use 2kW on a canal once the boat is underway and, of course, a huge advantage of electric power is that you use nothing whatsoever when the boat is stationary such as in a lock.
So in a day of 6 hours cruising, you’ll probably have used 5 hours x 2 kW = 10kWh power (I’ve said 5 rather than 6 to allow for those times when the boat is stationary)
The question for self-sufficiency then is whether you can regenerate that power, in what timescale, and without plugging into a shoreline.
On a 57 foot long boat (which is entirely typical), you might be able to fit 1.5kW of solar panels. Why not more? Bear in mind that the roof also has to store the gangplank and boat pole and for many liveaboards, will also be a general storage space for bags of coal, wood and other miscellany. Plus you inevitably end up walking on the roof when operating the locks.
Thus you simply don’t have as much roof space for solar panels as the boat length would have you imagine. In fact, a 57 foot boat will usually only have 40 feet of roof space because the bow, well deck and rear deck do not have roof area.
With a 390W solar panel being approximately 2m x 1m and therefore lying lengthwise on the roof, you’ll get six such panels if you totally cover the roof. In reality, allowing for a rear hatch and the aforementioned gangplank etc, you’ll probably fit a maximum of four panels which is about 1.5kW of solar generation.
That sounds great in theory; since we need to generate 10kWh for our theoretical daily use, give it about 7 hours of daylight and we’d be recharged. Right? (7 hours x 1.5kW being 10.5kWh)
Wrong. Firstly, charging is not 100% efficient so it will take longer than that. Secondly, (unless you’re using expensive Lithium batteries for your powerpack) batteries take less charge as they get more full, so you need even longer to get them back up to near 100%.
The biggest drawback of all however is the simple fact that the rated 1.5kW of the solar array is based on the panels working at maximum, in direct sunlight, pointed directly at the sun. This is just not going to happen very often.
Not only are a lot of the canals shaded by trees which spoils the morning and evening sunlight but the panels will likely not be pointing optimally through the day unless you rig up some kind of automatic powered turning mechanism. This couldn’t run while you move the boat because any raised panels might get chipped off when you go under a bridge or through a tunnel.
Even more crucially, the UK just doesn’t get that much sun except in peak summertime and even then it’s variable. In winter there’s usually very little due to overcast skies and rain and snow and the rest of our climate. The hours of daylight are much shorter too. In spring and autumn things are a little better but it will be very dependent on there being clear sunny days for several hours.
To summarise: in summer, an off-grid pure electric strategy could work provided you have good sunshine hitting the panels all day and if you rest the boat for a day after each day you move it (or move for fewer hours each day).
In spring and autumn you’re likely to need a generator to complement whatever the solar brings in unless you’re happy to wait for several days to recharge between each move.
In winter, forget moving on solar power alone, it’s just not going to happen.
 Actually, Russell Newbery engines are still produced but they have that vintage ‘look’ and feel.
 Narrowboats are 6’10” wide at the base but come in by at least six inches on either side for the gunwales and then tend to have slightly sloping panels for the cabin sides so the roof width is substantially less than the hull width would suggest.