Emily Hartley
Speed Is the Biggest Lever You Have
Almost every narrowboat engine is happiest running just above tickover, and the fuel figures prove it. A well-loaded 45–55ft boat with a modern diesel will typically burn somewhere between 1 and 1.8 litres an hour at canal cruising speed — roughly 2.5 to 3mph. Push towards 4mph and that figure can double, because drag rises steeply with speed and a displacement hull keeps digging a bigger hole in the water the harder you ask it to go.
The practical rule is this: if you are making a breaking wash, with white water curling off the bow and slapping the bank, you are burning money and chewing up the towpath edge. Find the setting where the boat is moving steadily, the stern wave runs flat behind you and the wash is no more than a gentle ripple. On many engines that sits around 1,000 to 1,400rpm, though it varies with depth. Shallow stretches demand more power for the same speed, so ease off where the pound is thin and make your time up where the channel is deep.
Lock work rewards patience as well. Approach slowly enough to glide in, using the throttle only to correct your line. Use the boat's momentum rather than revving to close the last few feet, and once you are safely tied alongside a lock landing, there is no harm in stopping the engine while you wait.
Servicing and the Propeller: Small Neglect, Big Bills
An engine that is running poorly will drink fuel to compensate. The good news is that most of the fixes are cheap and can be done by a careful owner with basic tools.
- Change the oil and filters at the intervals in your manual — typically every 100 to 250 engine hours — and keep the air filter clean. A choked filter richens the mixture and wastes diesel.
- Have injectors checked if the exhaust is smoky or the engine hunts at idle. Poor spray patterns waste fuel and can wash bores over time.
- Keep the cooling system healthy. A worn raw-water impeller or a clogged weed filter makes the engine run cool and inefficient, and a failed thermostat wastes fuel on every trip.
- Check the propeller regularly. A prop fouled with weed, fishing line or a plastic bag can add ten per cent or more to your fuel consumption without you noticing much except a slightly sluggish feel.
Propeller choice matters too. A prop that is too coarse for the engine forces it to labour, while one that is too fine makes you rev harder for the same speed. If you have never had yours matched to the boat, it is money well spent.
Trim, Weight and a Clean Hull
A boat that sits bow-down or lists to one side drags more water. Move heavy items — toolboxes, spare batteries, water containers — towards the middle and low down, and think about where your fresh water tank sits. Filling at the last water point before a long run rather than carrying a full tank everywhere can save a surprising amount over a season.
Hull condition is the other quiet thief. A layer of slime, weed and freshwater growth adds friction across the entire underwater area. Regular blacking and, where appropriate, an anti-fouling coating will pay for itself in fuel and in the general health of the steel. It also makes the boat nicer to steer.
Plan the Route and Share the Locks
Route planning is free fuel. A little thought before you cast off can cut hours of unnecessary engine running.
- Work with the waterway's rhythm: tackle lock flights in the morning when volunteers and other boaters are about, and avoid arriving at a staircase just as a hire fleet turns up.
- Share locks and flights wherever you can. Two boats moving through a flight together take barely longer than one, and each engine works less hard for the same distance covered.
- On river sections, travel with the current rather than against it. Planning a passage around the tide can halve the fuel needed for a long stretch.
- Avoid dead runs. If you need shops, water or a pump-out, plan to stop there on the way rather than making a special trip.
Heating, Charging and Idle Hours
Long idling is the enemy of both your fuel tank and your engine. Extended running at tickover to charge batteries glazes bores, dilutes the oil and returns very little charge. Better to run the engine under load for one solid hour than to idle it for three short bursts.
For warmth on a long winter journey, a solid fuel stove is far cheaper per hour than a diesel heater drawing from the main tank. If you do rely on a diesel heater, use it to take the chill off rather than running it all day. A solar panel and LED lighting will take the pressure off your alternator, meaning fewer charging hours in total.
Know Your Numbers
You cannot manage what you do not measure. Fill the tank to the brim, note the engine hours, and log every refill with the litres taken and the hours run. After a few weeks you will know your boat's true litres-per-hour figure, and any sudden change will tell you something is wrong — a fouled prop, a dragging brake or a fuel leak.
Buy in sensible quantities, use a calibrated dipstick so you never run low, and top up before long stretches where fuel boats or marinas are scarce. Do all that, keep the speed gentle and the servicing up to date, and you can knock a meaningful amount off your diesel bill without the trip feeling any slower.
