Displacement Hull Fuel Calculator
A displacement hull moves slowly and economically, pushing water aside rather than rising onto a plane. Its fuel burn is governed by the power the engine actually delivers, not its rated maximum. This tool estimates litres per hour from the engine's continuous power, the fraction of that power you cruise at, and the engine's brake-specific fuel consumption (BSFC), the grams of fuel burned per kilowatt-hour. Enter your figures, or use the typical marine-diesel BSFC default, to find hourly burn, fuel for a passage of a given duration, and the range a tank gives you. All figures are user-editable so you can match your own engine's data plate and tank.
Displacement hull fuel formula
Power used = continuous power * load
Mass flow (kg/h) = power used * BSFC / 1,000
Fuel L/h = mass flow / fuel density
Passage fuel = fuel L/h * hours
Endurance = usable tank / fuel L/h
Brake-specific fuel consumption gives grams of fuel per kilowatt-hour of output. Multiply by the kilowatts actually used and divide by 1,000 to get kilograms per hour, then divide by fuel density to convert mass to volume. Marine diesel BSFC typically runs 200 to 230 g/kWh near best efficiency; lighter loads burn more per unit of work.
Worked example
A 100 kW engine cruised at 70 percent load delivers 70 kW. At a BSFC of 210 g/kWh that is 70 * 210 / 1,000 = 14.7 kg/h. Dividing by a density of 0.84 kg/L gives 17.50 L/h. An 8-hour passage burns 140.00 L, and a 400 L usable tank gives an endurance of 22.86 hours.
Frequently asked questions
What is brake-specific fuel consumption?
Brake-specific fuel consumption (BSFC) is the mass of fuel an engine burns to produce one kilowatt-hour of output at the crankshaft, usually quoted in grams per kilowatt-hour. A lower BSFC means a more efficient engine. Marine diesels are most efficient near their best-economy load and burn proportionally more fuel at very light or very heavy loads.
Why use engine power rather than boat speed for fuel burn?
Fuel is consumed in proportion to the work the engine does, which is power over time. Boat speed relates to fuel burn only through the resistance curve of the hull, which varies with hull form, displacement, fouling, and sea state. Working from delivered power and BSFC gives a direct, physically grounded estimate that does not depend on those uncertain factors.
What cruise load fraction should I use?
Many displacement-boat owners cruise at 60 to 75 percent of continuous engine power for a balance of speed, economy, and engine longevity. Check your engine's load against its power curve, or use a fuel-flow meter to confirm. Enter your own measured figure when you have it; the load fraction is a user-editable input.
Does this include a fuel reserve?
No. The endurance figure is the time the usable tank lasts at the calculated burn rate, with no margin. Good practice is to plan a passage to use no more than two thirds of usable fuel, keeping a third in reserve for headwinds, foul current, and diversions.
Official sources
- U.S. Energy Information Administration: diesel fuel properties and energy content.
- U.S. Department of Energy: fuel conversion factors.
Reviewed by the CalculatorHub team, edited by James Graham, 19 June 2026. See our methodology.