Priya Patel
Why a Simple Fuel Log Is Worth the Trouble
Diesel is one of the quiet costs of narrowboat life. You fill the tank, forget about it for a few weeks, then wince at the bill for 150 litres. Because the tank is big and the engine is frugal, a problem can smoulder for months before it becomes obvious. A modest daily fuel log changes that. In ten minutes a week you build a record that tells you what an hour of cruising really costs, flags engine trouble before it strands you at a lock flight, and lets you budget for a fortnight on the Grand Union without guesswork.
What to Note Down Each Day
Keep it simple, but keep it consistent. At the end of a day's cruising, jot down:
- The engine hour meter reading at start and finish, so you know exactly how long the engine ran.
- The litres added at every fill, plus the price you paid per litre.
- Where you were and what sort of water you were on — canal, river or tidal.
- Anything that made the engine work harder: a long lock flight, pushing against a current, towing, or a day spent at tickover charging the batteries.
- Heating use if your diesel heater, stove or boiler draws from the same tank.
- Oddities — black smoke, a rough idle, weed on the prop, an overheating warning.
That last column matters more than people expect. Numbers only become meaningful once you know what the boat was doing when they were recorded.
Working Out Your Litres per Hour
Fuel gauges on narrowboats are famously vague, so don't trust the dial. Work from fill to fill instead. Fill the tank right to the brim, note the hour meter reading, then run as normal until the next brim-full fill. Divide the litres you put in by the engine hours you've covered. That gives you litres per hour.
As a rough guide, a well-maintained modern diesel in a 50 to 60 foot narrowboat burns somewhere around 1 to 1.5 litres an hour at cruising revs. A vintage engine, or a day spent punching up a river against fresh, can easily double that. Measuring in hours rather than miles is the right approach on the canals, because locks, queues and shallow stretches distort any per-mile figure.
Reading the Warning Signs
Once you have a baseline, the log starts earning its keep. A sudden jump in litres per hour usually points at something physical: weed wrapped round the prop, a clogged air filter, a tired injector, an engine running cold because the thermostat has failed, or a propeller that no longer suits the boat's weight and trim. A gradual rise over a season can simply mean the hull needs blacking and is dragging more water.
An unexplained drop deserves just as much attention. A sticking hour meter flatters your figures, and so does a tank that is quietly weeping into the bilges. If the log doesn't add up, have a sniff around the engine bay and check for a diesel sheen under the engine.
Watch too for the classic signs of diesel bug — water in the tank, slime in the filter bowl, rough running after a fill from an unfamiliar source. Log your filter changes alongside your fill-ups and patterns emerge quickly. A filter that clogs every few weeks is telling you something the fuel figures alone won't.
Planning Fuel for Longer Cruises
With a reliable litres-per-hour figure, longer journeys become arithmetic rather than anxiety. If you average 1.3 litres an hour and plan five hours of cruising a day, that's around 6.5 litres daily, or roughly 45 litres for a week. Add a margin for river sections, delays and a day of hard charging, then decide where you'll top up.
Two practical habits help. First, never run the tank near empty — sediment stirs up and blocks filters at the worst moment. Second, note the price per litre at each fill in your log. Canal-side boatyards, marinas and fuel boats all vary, and knowing what you paid last time makes it easy to spot a fair deal. If you cruise through winter, work out your heating consumption separately, or your engine figures will look alarmingly thirsty.
Habits That Make Logging Stick
The best system is the one you'll actually use. An A5 notebook kept in the engine bay works well, as does a note on your phone or a simple spreadsheet with a row per fill-up. Fold the hour meter reading into your pre-start checks — oil, water, weed hatch, hours — and it becomes second nature rather than a chore.
At the end of each season, do a five-minute review. Compare this year's litres per hour with last year's, glance at your filter changes, and note anything that shifted. Boaters who keep this small record tend to spot problems early, budget with confidence, and enjoy the cut that little bit more, knowing exactly what the day's cruising has cost them.
